Crapemyrtle (Lagerstroemia spp.) is one of the most popular deciduous flowering trees in the United States, generating an estimated market value of up to $70 million per year (USDA 2001, USDA 2009, USDA 2014, USDA 2019). Its versatility as an ornamental plant and long blooming period makes it a widely used choice in landscape.

Crapemyrtle also plays an important role in the local ecosystem in the southeastern United States (Riddle and Mizell III 2016). While the flowers do not produce nectar, they offer a significant source of pollen to attract pollinators such as bees (Harris 1914, Kim, Graham et al. 1994). Studies have shown that crapemyrtle pollen is a major protein source with a nutritional makeup that is suitable for bee consumption (Nepi, Guarnieri et al. 2003). The extensive and heavy blooming of crapemyrtle during summer months (Pounders, Reed et al. 2006, Pounders, Blythe et al. 2010) make it a critical food source for pollinators, especially when many other flowering plants are not in bloom (Lau, Bryant et al. 2019). Due to its wide distribution, crapemyrtle provides excellent pollen sources for both native and non-native bees in the United States.

Crapemyrtle is relatively easy to maintain in the landscape with few severe diseases and insect complications. However, pest issues such as aphids, scale insects, Japanese beetle, and metallic flea beetles, and diseases such as powdery mildew and Cercospora leaf spot (caused by Psedocercospora lythracearum) may require proper management.

Crapemyrtle is a popular and versatile ornamental plant known for its vibrant flowers, wide range of color options, attractive bark features, and ability to thrive in various landscape settings. With its wide range of cultivars and adaptability to different regions, crapemyrtle has become a staple in gardens, parks, and residential and commercial landscapes.

To meet the market demand for crapemyrtle, the nursery industry utilizes field production and container production to produce crapemyrtle suitable for different landscape applications. Crapemyrtle plants are available in various sizes, ranging from small "liners'' or transplants to large caliper trees of 6 feet and larger. Smaller plants are commonly produced and sold in trays or containers, while larger trees are mechanically harvested as bareroot or balled and burlapped.

Field production involves growing crapemyrtle trees in the ground, typically in dedicated production fields. This method allows for the cultivation of larger specimens but requires specific management considerations for harvesting, transportation, and storage. However, notable issues regarding field production include the potential loss of field soil and root mass during the harvesting process for balled and burlapped plants.

On the other hand, container production involves growing crapemyrtle in pots or containers, providing flexibility in terms of space, mobility, and controlled environments. Container-grown crapemyrtle trees are more popular among retail nurseries, landscape professionals, and homeowners seeking smaller-sized trees for immediate impact. However, container production is limited when it comes to producing large caliper trees due to the maximum available container size, typically up to 500 gallons (Braman, Chappell et al. 2015).

Both field production and container production have their unique considerations and techniques, which are implemented by nursery professionals to ensure the successful growth, health, and market readiness of crapemyrtle trees. From site selection and soil preparation to propagation, irrigation, fertilization, pest management, and pruning, a comprehensive understanding of production practices is crucial for producing high-quality crapemyrtle specimens. In this section, the key production practices involved in both field-grown and container-grown production of crapemyrtle are outlined to provide valuable insights that contribute to the successful cultivation of crapemyrtle, enriching outdoor spaces with its beauty and charm.

Field Production

Site selection and soil preparation

Crapemyrtle thrives in sunny locations, making it essential to choose a bright and sunny spot for planting. Lack of sunlight can cause reduced flowering (Wade and Williams-Woodward, 2009), and cultivars that are known for their dark foliage tend to have greener foliage under a less sun conditions. The favorable growing c a great option for difficult locations that are hot and dry, where many other ornamental plants struggle to grow. When planting, spacing is a crucial factor to consider as some cultivars can grow over 20 feet tall, with a canopy spread between 5 to 20 feet (Niemiera, 2018). Limited planting space will lead to excessive pruning when the plant reaches its mature form.

As a woody ornamental, crapemyrtles are adaptable to various soil conditions and thus well suited for urban areas and even more challenging soils. Crapemyrtles grow best in soil that is heavy loan to clay texture with a pH between 5.0 to 6.5 (Egolf, 1987). While crapemyrtles can tolerate poor soils, the ideal soil should be nutrient-rich and well-drained, as poor soil can hinder growth and development. Proper preparation can ensure that the plant will have access to the necessary nutrients and water it needs to thrive. A soil test may be conducted to assess various soil parameters, including pH level, organic matter content, nutrient levels (such as nitrogen, phosphorus, and potassium), micronutrient levels, and soil texture (proportions of sand, silt, and clay). Based on the findings, targeted soil amendments and fertilization can be done to optimize soil conditions for healthy crapemyrtle growth.

In nursery productions, additional factors such as operation space (turning radius for farming vehicles), topography (slope), and access to irrigation water need to be considered for site selection. A proper design of the planting rows and establishment of grassed waterways and buffer strips are effective in reducing soil losses and water runoff. Contour buffer strips of permanent, herbaceous vegetation should be established on sloping cropland and be at least 15 feet (4.6 m) wide to meet the conservation standards by USDA (USDA, 2014b).

Planting

Before planting, it is important to prepare the tree by removing any damaged or broken branches and roots. Digging the hole should be done at a depth that is slightly larger than the root ball. When planting, the root ball should be placed in the hole and back-filled with soil. It is important to avoid planting the tree too deep (no deeper than it originally grew in the container or field), as this can lead to poor drainage and hinder growth.

As an essential step in the planting process, watering is recommended for newly set transplants within 24 hours after planting to help firm soil around roots and eliminate air pockets (Braman et al., 2015). Newly planted trees need frequent watering to help establish roots and encourage growth. It is important to water thoroughly and consistently, ensuring the soil remains moist but not overly saturated.

Watering

Proper watering promotes the health and growth of crapemyrtle trees, and the watering requirements can vary depending on the growth stage and planting situation. Watering crapemyrtle at the base of the plant, not on the foliage, prevents the spread of foliar diseases. Additionally, watering in the morning or evening when the temperatures are cooler helps to reduce evaporation and water loss. Early morning (before 10 am) or late afternoon/evening (after 4 pm) are ideal for watering, as it allows sufficient time for foliage to dry before nightfall.

For newly planted crapemyrtle, it is important to water frequently in the first few weeks to help the tree establish roots. Watering should be done deeply, at least once or twice a week, depending on the weather conditions. A good rule of thumb is to water until the soil is moist to a depth of at least six inches. As the tree becomes established, watering frequency can be gradually reduced.

Established crapemyrtle trees in the landscape typically have deep root systems and can tolerate periods of drought without needing additional watering. They can often rely on natural rainfall to provide enough moisture, unless experiencing extended periods of drought. In such cases, supplemental watering may be necessary to prevent stress on the tree and enhance flowering (Wade and Williams-Woodward, 2009). It’s important to monitor soil moisture levels and only water when the soil is dry to a depth of a few inches. Overwatering can be detrimental to the tree’s health and may lead to root rot.

Fertilizing

Crapemyrtle, once established, generally has low fertility requirements but can benefit from regular fertilization to promote lush growth and abundant blooming. Conducting a soil test is recommended to assess important soil parameters such as pH and nutrient levels, enabling precise fertilizer recommendations. Following a proper fertilization regimen optimizes plant growth while minimizing the risk of groundwater pollution through reduced runoff and leaching of excess nutrients. Based on the soil test results, it is advisable to incorporate lime, superphosphate, and other nutrients before planting to adjust pH and improve the soil’s nutritional balance. Crapemyrtle trees respond favorably to slightly acidic soil (pH 6.0-6.5) and general-purpose garden fertilizers can be used when needed or based on soil test. Alternatively, organic fertilizers like bone meal or rock phosphate can also be used to supplement nutrient needs.

Fertilizers are available in various forms, such as powder, granular, or liquid, and can be applied through different methods, such as broadcasting and placement of solid fertilizers, and fertigation using liquid fertilizers. Broadcasting involves the uniform distribution of fertilizers across the entire field either through basal application or top dressing. On the other hand, placement refers to the deliberate positioning of fertilizers at specific locations within the field. Broadcasting can be used prior to planting to adjust the overall nutrient balance of the soil, but it also promotes weed growth. Compared to broadcasting, placement is recommended for applying small amount of fertilizer, and it can be used to avoid weed pressure and lower nutrient runoff. For applying liquid (or soluble) fertilizers, fertigation is usually used, which the fertilizers are applied through irrigation water.

In the nursery production settings, an initial application of 50 lbs per acre nitrogen (N) to 6-to-8-inch soil can suffice the growing needs of woody plants such as crapemyrtle while minimizing nutrient runoff. In subsequent years, rather than broadcasting the fertilizer at the initial rate, the N fertilizer should be placed within the root zone as a side dress at the rate of 0.25 to 0.5 oz. N per plant (Smith, 2014). Alternatively, controlled-release fertilizer has also been developed for field application, allowing a single application to last the growing season.

During crapemyrtle container production, most growers in general incorporate controlled-release fertilizers (CRFs) in the substrate to provide necessary nutrients for plants to establish its root system and support new growth. Hence when transplanting a new crapemyrtle tree in the landscape, mixing fertilizers such as CRFs into the soil might not be necessary, or be handled as needed according to a soil test. In the landscape, crapemyrtles are generally very vigorous growing plants, but when growing in poor soil conditions might require occasional applications. For established crapemyrtle trees, fertilization might be performed as needed during the growing season, typically in spring to early summer when the tree is actively producing new growth. Fertilization in late summer should be avoided as it will interfere with the plants’ ability to harden off in the fall. Established crapemyrtle trees in landscape may not require fertilization if they are growing in nutrient-rich soil and receive regular rainfall, as they may be able to obtain the necessary nutrients naturally. Monitoring the tree’s growth and health can help determine if supplemental fertilization is necessary.

Propagation

Crapemyrtle can be propagated using various methods, including stem cuttings, root cuttings, or seeds. The most commonly used method is through semi-hardwood cuttings taken during late spring or early summer. In the southern US, the propagation rates of crapemyrtle through cuttings drop quickly by September. In northern states such as Michigan, the cutting propagation success starts dropping as early as July or August. Cuttings should measure three to six inches in length and have three to four nodes. It is advisable to remove the leaves from the lower half of the cutting, leaving a few leaves at the top. While crapemyrtle cuttings can root without hormones, rooting powder or solution can enhance rooting success and speed up the process. Once prepared, the cuttings should be inserted into a well-draining rooting medium and kept in a moist and shaded environment.

Root development usually occurs within three to six weeks while rooting success in cuttings varies across different times of the year. Cuttings taken during late spring to early summer typically exhibit rooting within three to five weeks, indicating this period as optimal for propagation efforts. Conversely, cuttings obtained in early spring show a notably lower rooting success rate. Additionally, cuttings derived from flowering plants or those taken in late summer are less likely to root effectively. Therefore, for optimal results in crapemyrtle cutting propagation, it is advisable to select cuttings during late spring to early summer.

Propagation by dormant cuttings has been used as a viable method in nursery production. Rooting success will be lower using this method, but it allows growers to continue production during slower seasons and increase production volume. 4-to-6-inch cuttings (approximately the diameter of a pencil) can be prepared and treated with a moderate IBA concentration before placing into a warm greenhouse with enough mist to prevent dehydration. The cuttings can be nicked or scarred on the basal end helps with IBA uptake and promoted callas growth.

For propagating crapemyrtle from seeds, collect mature seeds from fruit pods in the fall and sow them in a well-draining potting mix. Keep the soil consistently moist and warm, and seedlings should emerge within a few weeks. Whether using cuttings or seeds, it is crucial to maintain soil moisture and provide shade to prevent drying. Once the new plants have established roots, they can be transplanted to their permanent location in the landscape, preferably during dormant seasons such as winter (Wade and Williams-Woodward, 2009).

It is important to note that propagation practices can vary among different growers and nurseries. The decision on leaf removal during propagation often depends on balancing the need for photosynthesis and the need to reduce transpiration and conserve moisture. In the industry settings, the labor cost for certain propagation practices should also be taken into consideration. For example, Propagation by seed is never used for nursery production. Most commercial production is through asexual propagation. Seed propagation is useful in breeding programs to obtain new traits. Those seedlings of interest are asexually propagated. Commercial nurseries also seldom propagate crapemyrtles by root suckers.

Pruning

Crapemyrtle is known as a low-maintenance plant with little or no need for pruning when appropriate cultivar and correct placing were implemented. If necessary, pruning can be done for different purposes, such as promoting shape, thinning the tree, and maintaining size. While pruning is not essential for promoting flowering, it is known that proper pruning can lead to new vegetative growth that produce denser flower clusters (Gilman and Black, 2005) and higher number of flowers (Dihingia and Saud, 2016). For some cultivars, pruning to remove spent flower blossoms or the developing seed heads can stimulate new growth as well as more rounds of flower display (Gilman and Black, 2005; Wade and Williams-Woodward, 2009). However, over-pruning and incorrect pruning practices may damage the tree and produce undesirable plant architecture (Polomski and Shaughnessy, 2006).

Pruning is preferably done during the dormant season for crapemyrtle, typically in late winter or early spring, to avoid interfering with the blooming season. Since crapemyrtle produce flowers on new growth, pruning during the growing season can lead to loss of flower buds (Wade and Williams-Woodward, 2009). Pruning should be avoided in the fall, especially near the first frost, since it prevents plants going into full dormancy, leading to loss of cold hardiness of the crapemyrtle (Hayns et al., 1991).

Depending on the intended purpose, pruning can be done at early stages in the crapemyrtle’s development. For example, when pruning for tree form, the focus is on removing lower branches to create a clear trunk and a well-defined canopy. The main stem should be trained to grow straight and tall, while any lateral branches should be pruned back to encourage upward growth. The ideal tree form for crapemyrtle is a single-trunk or multi-stemmed tree with a rounded or vase-shaped canopy. Removing lower branches allows for better air circulation and reduces the risk of disease and insect infestations. It also helps to create a cleaner, more aesthetically pleasing look.

On the other hand, when pruning for a shrub form, the focus is on creating a full and bushy plant with multiple stems. This can be achieved by leaving the lower branches intact and pruning the upper branches to promote branching and fuller growth. The shrub form is also a suitable option for smaller cultivars or for those grown in containers. Regardless of the plant form (single-, multi-trunk, or shrub), it is helpful to periodically remove suckers as a part of maintenance for mature crapemyrtle in the landscape. Suckers are unwanted shoots that grow from the roots and base of the tree. Removing these suckers ensures that the crapemyrtle focuses its energy on growing upward instead of outward.

Dormant pruning of the plant to 3-4 inches above the soil has been shown to be effective in incorporating crapemyrtles into smaller garden landscapes, or to encourage flowering at a lower height. Such a method is particularly beneficial when the landscape design requires smaller flowering shrubs, ensuring that the crapemyrtles remain proportionate to the garden's scale. Dwarf and semi-dwarf varieties of crapemyrtle are especially responsive to this type of practice, producing lush, manageable growth suited to compact spaces.

When it comes to maintaining crapemyrtle in the landscape, there are several pruning practices that were commonly used, including tipping, pollarding, and topping (Knox and Gilman, 2010). Tipping (also known as ‘tip pruning’, ‘rounding over’, or ‘pencil pruning’) is considered light pruning where only smaller-diameter branches on the outer edge of the canopy were removed (Figure 3). ‘Tipping’ practice can thin out the canopy by removing unwanted or dead branches with empty seed pods from the previous season while retaining the nature form of the crapemyrtle. However, tipping is very time consuming, thus it may be leading to the prevalence of more aggressive pruning practices such as pollarding and topping.

Pollarding and topping, on the other hand, are considered ‘hard pruning,’ where larger-diameter branches are removed. Pollarding is an annual pruning technique that involves making an initial cut on a multi-year-old branch. Subsequently, all sprouts that emerge each year are trimmed back to the original cutting area, creating a ‘pollard head.’ (Figure 3) Over time, the wound wood around the cut area swells, forming the pollard head storing significant energy for sprouting in the following season. Pollarding is typically done to confine plants to a specific size indefinitely, allowing crapemyrtle to regrow and maintain the same tree form each year.

Figure 3: Three different pruning methods for crapemyrtle include: (A) Tipping, where only smaller-diameter branches on the outer edge of the canopy are removed; (B) Topping, where large-diameter branches are cut; and (C) Pollarding, where crapemyrtles are trimmed back to the same cutting area each year, creating a bulbous growth referred to as a 'pollarding head.'

Similar to pollarding, topping (also known as heading, stubbing, rounding, or dehorning) removes large-diameter branches, but the cuts were not made to the original cutting area, thus no ‘pollard head’ is formed (Figure 3). The topping method results in the shortening of all branches, hence, can also be used to restrict the size of a crapemyrtle. Compared to other selective pruning methods, topping is the least time-consuming method, however, study has shown that topping creates unstable branching structure and decaying or dead branches in the canopy (Gilman and Knox, 2005).

It is generally advised to avoid over-pruning crapemyrtle, as it may be unnecessary and result in an unappealing appearance, particularly in winter and if the natural form of the tree is desired. The practice of ‘hard pruning’ such as topping can have negative effects on the health of the crapemyrtle, potentially leading to pest and disease issues (Appleton et al., 2009). While it is true that crapemyrtle flowers only on new growth each season, excessive pruning to remove empty seedheads from the previous season is unnecessary, as they will naturally drop when new growth emerges.

Container Production

Selecting Containers

Selecting the right container for crapemyrtle involves considering factors including the physical properties of the container (e.g., size, material, functionality, and drainage) as well as the planting time frame. Growing crapemyrtle in containers restricts and slows down their growth, which is desirable if a miniature-sized plant is desired due to limited space. Crapemyrtle can also be grown as a bonsai tree. However, it’s important to consider the mature plant size of the crapemyrtle, which varies greatly between different species or cultivars. Certain species of crapemyrtle, such as L. speciosa, are fast-growing plants that can reach up to 30 to 60 feet in height and approximately 30 to 40 feet in width (Gilman, Watson et al. 2019). Therefore, the container needs to provide ample room for the root system and accommodate the size and growth habit of the plant. An overgrown crapemyrtle in a container would easily topple over, especially when placed outdoors.

The effects of container size have a significant impact on the overall plant growth (NeSmith and Duval 1998). Moreover, the length of time the plant is likely to be spent in the container should be considered, as the transplanting timing affects greatly the vegetative growth on the finished plant (Knight, Eakes et al. 1993). In general, plants grown in larger containers have greater plant leaf area, and shoot and root biomass (Cantliffe 1993). Therefore, when the goal is to encourage growth, it is necessary to transplant crapemyrtles into larger containers once the plants reach their maximum growth potential in the original container. To transplant small plants or liners (containers < 8 inches in diameter) into larger containers, it is recommended to choose containers that are 1 to 2 inches wider than the current root ball. For transferring larger plants (containers > 10 inches in diameter), choosing 2-inches to 3-inches wider than the plant’s root ball is ideal (Moore and Bradley 2018).

Most crapemyrtle sold by the nursery are planted in plastic containers. Plastic containers are lightweight, durable, and easy to handle, making them a practical choice for long-term use. Retail garden centers generally offer a variety of container sizes including trade #1 (2.5L), 2 gallon (g), 3g, 5g, 7g, 10g, and 15g, ranging from 15.24 to 44.45 cm (6–17.5 in) in diameter, allowing flexibility in choosing the appropriate container for different stages of plant growth. According to a recent survey, the three most popular sizes for crapemyrtles are 15 g, 30 g, and 45 g (Marwah, Zhang et al. 2021). For nurseries, the largest volume of units of crapemyrtles sold are 2 and 3g. While 1-gallon size provides the lowest price point, consumers are looking for a balance between cost-effectiveness and plant size during their purchase.

Plastic containers also retain moisture better than clay pots, which can be advantageous in hot and dry climates (Moore and Bradley 2018). There are also plastic air-pruned containers that promote a more fibrous root system, which greatly affects a plant’s health and future establishments (Cooley 2013). Additionally, cupric hydroxide-treated (product trade name: SpinOut™) containers were found to be effective in controlling root circling and deflection when growing crapemyrtle, with no observed negative symptoms (Beeson Jr and Newton 1992).

While rarely used in commercial production settings, there are other container types utilizing different materials such as clay, wood, and fabric, available for consumers. Clay and wood containers provide better breathability for the roots as they allow air exchange through the container walls, preventing root suffocation and promoting overall plant health. They also have an aesthetic appeal that enhances the visual appeal of the landscape. However, clay pots are heavier and more prone to breakage compared to other materials. On the other hand, wood containers, such as cedar or redwood, provide natural durability (up to ten years) and add a rustic look to the landscape (Moore and Bradley 2018).

Fabric containers, known as grow-bags, are lightweight, portable (foldable), and offer excellent drainage. Fabric container is a hybrid form of production system between field and container production, as the container can be used above ground (similar to other types of container), or buried under soil, leaving only the top inch of the fabric exposed above ground (Gilman, Knox et al. 1994). Grow-bag confines plant root within its porous fabric barrier, leading to the effects of root pruning and root branching. However, a study compared Natchez crapemyrtle transplanted from field and grow-bag and found mostly equivalent plant performance in these two productions (Tilt, Gilliam et al. 1992). Nevertheless, fabric containers offer several potential benefits over traditional field production. They enable plants to retain a greater portion of their roots during transplanting, which reduces stress on the plant. Furthermore, fabric containers simplify the logistics of nursery operations, including the shipping of bags to the nursery. They also contribute to a reduction in the shipping weight of the finished plants, making the transportation process more efficient.

The decision to utilize alternative production systems, such as grow-bags, may depend on the field soil conditions, which determine the ease of traditional field harvesting. Regardless of the material, it is crucial to ensure that containers have sufficient drainage or can be modified to allow excess water to escape. Adequate drainage prevents waterlogging, which can lead to root rot and other plant health issues.

Substrates

The media used to grow container plants is generally referred to as ‘substrate’, ‘potting mix’, and ‘growing media’, and they do not usually contain field soil. Field soils are generally too heavy and do not have enough pore space and drainage when placed inside container, thus unfit for container plant production. For cultivating container-grown crapemyrtle, proper substrate preparation includes the considerations of the substrate’s physical properties [e.g, total porosity, container capacity (i.e., water holding capacity), and air-filled porosity] and chemical properties (e.g., pH, electrical conductivity, and nutrient levels).

The substrate composition should have the ability to retain moisture while promoting proper drainage to prevent waterlogged conditions and provide adequate aeration for the roots. A typical substrate mixture for container-grown crapemyrtle includes a combination of organic and inorganic components such as peat moss or coconut coir for moisture retention, perlite or vermiculite for improved aeration, and pine bark or composted pine fines for structure and nutrient availability.

For outdoor container nurseries where large amounts of substrates are required, the input cost and availability of raw materials are also important factors to be considered. The most common substrate adopted by the U.S. nurseries include a mixture of pine bark, sphagnum peat moss, and sand, at varying ratio. Aged pine park (particle size ranging from 0.5 to 16 mm, with up to 30% under 0.5 mm) is generally preferred compared to fresh pine bark due to the enhanced water holding capacity (Bilderback 2017). In general, growers use a recipe of 80% to 100% aged pine bark, with addition of sand or peat moss to make up the rest (Braman, Chappell et al. 2015, Bilderback 2017). Sometimes sand and soil are added to increase the weight, which reduces container tip-over, but can also introduce pathogens. However, pine bark, especially when aged, is limited and time-consuming to acquire. Therefore, alternative materials to pine bark have been increasingly studied and used to lower the production cost.

Most alternative substrates are organic wastes such as shredded coconut husks (coir), rice hulls, peanut hulls, pecan shells, and other composted wastes (e.g., yard wastes, animal wastes, and hardwood bark). These organic matters need to be fully composted before using since unstable organic material tend to decompose and losing volume rapidly.

High wood-fiber content substrates such as clean chip residual (CCR), ground pine chips (PC), and WholeTree (WT) has been evaluated for their potential replacement for pine bark (PB) in crapemyrtle container production. Boyer, Gilliam et al. (2009) used CCR at varying sizes [screening size up to 3.18 cm (1.25 inch)] to grow ‘Hopi’ and ‘Natchez’ crapemyrtles in #1 container and found no difference in performance between the plants grown in CCR and PB. Marble, Fain et al. (2012) also demonstrated that both CCR and WT could be used to produce equivalent marketable crapemyrtle compared to PB. On the other hand, Wright, Browder et al. (2006) showed that crapemyrtle were larger when grown in PB compared to PC, which is attributed by the lower nutrient availability in PC. These studies suggest that alternative wood-based substrates could potentially replace the declining supply of PB, but testing should be done prior to the implementation of these materials to determine proper fertility adjustment needed.

In recent years, substrate stratification, a practice of creating ‘layered’ substrates inside containers, has been described as a potential solution for improving resource management in container crop production. Fields, Criscione et al. (2022) found that ‘Natchez’ crapemyrtle had greater root dry weight when grown in stratified substates where finer substate was placed atop of the coarser particles, compared to the unstratified controls. The placement of coarse particles at the bottom half of the container was shown to improve drainage and uniformity of water retention throughout the container profile. Similarly, adding drainage material like gravel or perlite to the bottom of the container promotes proper drainage in the containers.

Maintaining the appropriate pH and electrical conductivity (EC) levels in the substrate is crucial for optimal plant growth in containers. While the natural or properly aged pine bark is generally suitable for crapemyrtle growth (pH range 5.0 - 6.5), testing should be done to determine the pH and EC prior to the mass utilization of the substrate. The reading of pH and EC of the substrate can be obtained by testing 1 cup (236.6 mL) of the substrate mixed with distilled water, using a pH and conductivity testing pen or meter. Ideal pine bark are expected to have a low pH between 3.9 to 6.0 and conductivity range between 0.2 to 0.5 dS/m (mmhos/cm) (Bilderback 2000, Braman, Chappell et al. 2015). The pine bark should not be used if low pH (e.g, pH < 3.8) or high conductivity reading (e.g, 1.5 - 2.5 dS/m) are found as they are potential indicative of unfinished decomposing process and active anaerobic respiration inside the substrate pile. Once plants have established roots in the substrate, monitoring practices such as pour-through technique can be used to maintain optimal plant health and growth. The pour-through technique involves watering the plants sufficiently so that the excess water, or leachate, drains out and can be collected for analysis. By examining the leachate, growers can evaluate the nutrient content and salt accumulation within the container media, and adjust the fertilization as needed to correct any deficiencies or imbalances.

Good sanitation practices in storing and handling substrate are important to eliminate weed seeds, pests, and pathogens that could hinder plant growth. This can be achieved by using commercially available sterilized substrates and proper sterilization of production surface. 10% sodium hypochlorite solution or other commercially available disinfectant can be used to clean recycled containers.

For container nursery production, implementing proper sanitation practices helps minimize the risk of soil-borne diseases, ensuring the health of container-grown crapemyrtle. Bulk substrate inventories should be stored on a concrete slab at the highest elevation in the nursery to avoid contamination from the runoff from the growing areas. The potting bark inventory piles should be kept moisten, under 10 feet, and turned periodically (at least every 3 to 4 weeks), to prevent fire hazards. Frequent turning and mixing of the moisten bark also help prevent fungal colonization of the medium (Braman, Chappell et al. 2015).

Irrigation

Proper irrigation is crucial for the successful container production of crapemyrtle. The frequency and amount of watering depend on various factors such as container size, weather conditions, and plant growth stage. Generally, crapemyrtle planted in containers require more frequent watering than those in the ground. Containers tend to dry out more quickly than the ground, so daily watering may be necessary during hot and dry periods. It is important to monitor the moisture level of the substrate and water the plant when the top inch of substrate feels dry. When growing media containing peat moss or pine bark is used, it is important to avoid the media to dry out. Pine bark-based substrate can tolerate a certain degree of overwatering to suffice the irrigation needs, however, frequent over watering leads to the concern of nutrient leaching from the container (Braman, Chappell et al. 2015).

Irrigation types include overhead irrigation for smaller plants (e.g., in #1, #3, and #5 containers) or liners, while spray stakes or drip irrigation are primarily utilized for larger plants (e.g., in #7, #15, and #25). Best management practices commonly adopted by growers include cyclic irrigation, collection of runoff water, watering in the morning, and implementation of grass strips between production and drainage areas (Garber, Ruter et al. 2002).

Cyclic irrigation or cyclic microirrigation are irrigation practices to apply multiple rounds of subvolume of water instead of applying the total volume at a single time. Cyclic irrigation has several advantages in terms of resource      allocation, including reduction of irrigation water input, minimizing water runoff, and reduction of nutrient leaching, compared to continuous irrigation (Fare, Gilliam et al. 1994). For crapemyrtle, research showed that cyclic irrigation using the same volume of water has led to increased plant height, trunk diameter, and shoot dry weight, compared to the controls where irrigation volumes were provided at once (Beeson Jr and Haydu 1995).

Irrigation should aim to provide deep and thorough watering to encourage deep root growth. This helps the plants become more resilient to drought conditions. Water should penetrate the entire root ball and reach the bottom of the container. Avoid shallow and frequent watering, as it can lead to shallow root development and increase the risk of water stress. The leaching fraction from containers (irrigation drainage/total volume applied) and irrigation uniformity should be monitored to evaluate the efficiency of the irrigation system. Ideal leaching fractions for container crapemyrtle production should be between 0.15 and 0.25, but the value might be subjected to large fluctuation due to multiple factors including seasonal changes and pruning practices needed for crapemyrtle (Million and Yeager 2019, Million and Yeager 2021). Automated irrigation systems have been evaluated in recent years and may be implemented by nurseries to effectively lower the water input and maximize plant productivity.

Irrigation regimes may be adjusted according to the specific needs of the crapemyrtle variety and close monitoring. While current research that compares drought resistance levels for other crapemyrtle species and cultivars is limited, crapemyrtles are generally considered to be drought tolerant with little variation in different cultivars. Harp, Chretien et al. (2021) evaluated five ‘Ebony’ series crapemyrtle and ‘Centennial Spirit’ for their performance under low input landscape and reported no drought stress among all tested cultivars. On the other hand, (Cabrera 2009) reported the different salinity tolerance levels between ‘Pink Lace’, ‘Natchez’, and ‘Basham’s Party Pink’, and ‘Basham’s Party Pink’ was rated as having the most salt tolerance among the three cultivars. Therefore, monitoring the plants’ response to irrigation and adjusting watering practices accordingly is crucial to maintain optimal plant health.

Mulching the surface of the container can also help conserve moisture and reduce evaporation. Applying a layer of organic mulch, such as bark chips or straw, around the base of the plant helps to retain soil moisture, regulate soil temperature, and suppress weed growth. There is also an increasing number of growers adopting rice hulls as the mulching material. Studies showed that applying mulch on growing media allows for lowering irrigation volumes and can lead to increased gas exchange and overall plant growth of containerized crapemyrtle (Montague, McKenney et al. 2007).

Fertilization

Fertilization provides the necessary nutrients for healthy growth and abundant flowering of crapemyrtle grown in the container. Under-fertilization results in nutrient deficiencies and stunted growth. On the other hand, over-fertilization can lead to excessive vegetative growth at the expense of flowering and may even cause nutrient imbalances or burn the roots. Here are some key considerations for fertilizing crapemyrtle in container production.

Incorporating controlled-release fertilizers (CRFs) into substrates is a standard practice for fertilizing container plants over an extended period, providing consistent nutrient support to the plants. For general consumers looking to fertilize container-grown crapemyrtle, applying an all-purpose fertilizer with a balanced ratio of nitrogen (N), phosphorus (P), and potassium (K) is a good starting point. Fertilizer formulations such as 10-10-10 NPK with micronutrients (e.g., boron, iron, manganese, zinc, sulfur, magnesium, etc.) provide a well-rounded nutrient supply to support overall plant growth and flower production. For growers producing crapemyrtle at large scale, however, both the substrate and irrigation water should be tested to determine a fertilization regime. Substrates, substrate leachate (~ 50 mL) or plant tissue samples can be submitted to a commercial or university laboratory for a complete analysis of the nutrient levels to obtain specific guidance on fertilization needs (UMass 2023).

For growers, bark substrates in container production must have a complete package of micronutrients, and topdressing new crops of container production with CRFs is common. It is generally recommended to utilize CRFs with a fertilizer nutrient ration of approximately 3:1:2 (N:P:K) for container grown plants (Yeager, Gilliam et al. 1997). Best management practices recommended to supplement substrate with nitrogen at a rate of 3 grams per 1 gallon container (Bilderback 2017). For example, if a fertilizer containing 18(%) N is used, a total of 16.7 g of such fertilizer should be added to a 1-gallon container. Furthermore, studies have shown that fertilizer grades with lower amount of P and K, such as 18-1.7-6.6 and 19-2.6-10.8, are suitable for production of crapemyrtle in container (Shreckhise, Owen et al. 2020, Shreckhise, Owen et al. 2022). However, further lowering the P level in the fertilizer (using a 18.4-1.4-10.2 formulation) was found to negatively affect the shoot dry weight and overall plant quality (Shreckhise, Owen et al. 2022). Pine bark-based substrates were known to be prone to P leaching from containers during irrigation. Therefore, as suggested by Shreckhise, Owen et al. (2020), amending substrate with dolomite and a sulfate-based micronutrient fertilizer is considered a best management practice for crapemyrtle container production.

The placement of CRFs inside the container was found to influence the crapemyrtle growth. (Martin and Ruter 1996) has demonstrated that placing CRF at the north exposure of container has led to the increased plant size of crapemyrtle grown under outdoor nursery conditions. This phenomenon was attributed to the root growth pattern and the root zone temperature inside a sun-exposed container, and thus this practice could be most beneficial for crapemyrtle production in a hot and arid climate area.

When soluble fertilizer is incorporate in the irrigation water, it is important to consider not to utilize high concentration especially when constant feed fertigation is implemented. Cabrera and Devereaux (1999) has reported that 60 ppm N application was optimal in promoting the growth of ‘Tonto’ crapemyrtle, while higher concentration was shown to cause growth depression. Another study conducted by (Schluckebier and Martin 1997) showed that ‘Muskogee’ crapemyrtle had the best growth response to the fertigation with 50 microliter/Liter humic acid extract, but the higher concentrations (150 or 300 microliter/Liter) caused growth inhibition. Fertilization at a higher rate was also known to cause reduced flowering in crapemyrtles (Harrison 2006, Buxton 2017).

In addition to regular fertilization, it’s beneficial to supplement with micronutrients as needed. Micronutrients, such as iron, manganese, and zinc, are essential for proper plant growth and development. These can be provided through foliar sprays or incorporated into the potting mix, depending on the specific needs of the plants. For example, the foliar application of Moringa leaf extract was shown to promote growth and protect crapemyrtle plants against salt stress (Soliman and Shanan 2017).

Timing is important when fertilizing crapemyrtle in containers. Begin fertilization in early spring, once the plants have started to actively grow. Continue fertilizing throughout the growing season, typically until early summer. Avoid fertilizing during winter or periods of dormancy, as excessive vegetative growth prior to dormancy causes winter damage.

Regularly monitor the plants’ response to fertilization and adjust the fertilizer application as needed. Assess the overall growth, foliage color, and flower production. If the plants show signs of nutrient deficiencies or excessive growth, consider adjusting the fertilization regimen accordingly.

Pruning

Pruning practice for containerized crapemyrtle promotes plant uniformity, which is beneficial for nursery production (Zajicek, Steinberg et al. 1991).

In terms of economic value, crapemyrtle production has an irreplaceable role to play in the green industry. According to the latest USDA report, crapemyrtle generates an increasing market value (annual wholesale values and retail value) of up to $70 million per year, which almost doubled the number since 1988 (USDA, 2001, 2009, 2014, 2019). In 2019, 3.03 million plants with a combined value of $69.57 million were sold (figure 5).

Figure 5: Total sales of crapemyrtles in 1998, 2009, 2014, and 2019.

Figure 6: Crapemyrtle ecomonic values in different U.S. states.

Crapemyrtle Bark Scale (Acanthococcus lagerstroemiae)

Introduction of crapemyrtle bark scale

Crapemyrtle bark scale (CMBS; Acanthococcus lagerstroemiae), an invasive polyphagous sap feeder in the United States, has spread across 17 U.S. states in less than two decades, posing potential risks to the Green Industry.

Crapemyrtle bark scale is a hemipterous insect under the superfamily of Coccoidea (scale insects), which is closely related to other piercing-sucking insects such as mealybugs (Pseudococcidae), aphids (Aphididae), whiteflies (Aleyrodidae), and psyllids (Psyllidae). According to previous studies and observations, the number of CMBS generations within one-year ranges from two to four depending on the climate zones. In the Southeastern United States, CMBS-infested plants can be found in the field year-round, with up to four generations of CMBS being observed in Dallas, TX in 1 year. However, the lack of in-depth characterization of CMBS biological parameters, such as developmental stages, reproductive behavior, and fecundity, limits the research capacity to investigate controlling strategies based on insect biology and physiology.

Life cycle

The life cycle duration of CMBS varies according to different factors, such as temperature and host plant genetics. The average duration of one generation was estimated to be between 79 to 147 days under lab conditions (Xie et al., 2023). Under field and favorable environments, the mean generation time might be shorten, and it was observed that two to four generations of CMBS can occur in one year depending on the geological locations (Gu et al., 2014; Wang et al., 2016). The life cycle of CMBS males started from egg, which takes around 11 days to hatch when incubated under lab conditions at 25 °C. The developmental stages for individual insects, such as the 1st and 2nd instars, can be determined by monitoring molting events or by keeping track of the insect exuviae. The duration of 1st and 2nd instar stages are about 14 to 17 days and 29 to 68 days, respectively, depending on the different crapemyrtle used as host. The development of the male pupa was characterized as a three-step process (P1, P2, and P3 stages). Firstly, a P1 stage has been identified, as a 2nd instar forms the elongated ‘cocoon’ structure typically identified as a male sac in the field (Figure 7). Before P1, 2nd instar nymphs typically retract and detach their stylets from the plant and become mobile. Within a short period (24h), the male 2nd instar will relocate until finally settle down at a location, then start excreting wax to form the white male sac. After P1, the 2nd instar will pupate and push out the exuviates through the rear opening of the male sac. The duration of P1, P2, and P3 is around 4-8, 3-5, and 5-7 days, respectively. Hence, a total of three exuviates will be pushed out from the male sac before adult male emergence. After the molting of the pupa, the adult male usually stays in the pupa sac for several days before emergence. Once exiting the pupa sac, the adult male immediately roams the surrounding environment, presumably searching for the adult female’s presence. The development of CMBS males is complete metamorphosis, as pupa and adult male stages can be identified (Figure 7).

Figure 7 Detailed life history of crapemyrtle bark scale, Acanthococcus lagerstroemiae. E: Egg, N1: first-instar nymph, N2: second-instar nymph (N1 and N2 are indistinguishable in male and female), AF: adult female (or female third-instar nymph), MP sac: male pupa sac (consist of three stages: P1, P2, and P3), PREP: prepupa, P: pupa, GF: gravid female, OV: ovisac. Scale bars: 200 μm. Arrows represent chronological progression. Red arrows: molting events. Gray arrows and outline: adult males emerge and locate sessile adult females to perform the mating process (Xie et al., 2022).

Population dynamics

 From 2015 to 2017, a monitoring program was implemented across Texas, Louisiana, and Arkansas to track the seasonal population trends of CMBS. This program utilized double-sided tape wrapped around selected branches on a weekly basis. This method proved effective for capturing newly hatched crawlers, thereby revealing patterns of crawler activity throughout the year. The initial surge in crawler activity consistently occurred between March 26th and May 22nd in all studied locations and years, followed by several additional peaks, suggesting the presence of multiple generations of CMBS within a single year. The monitoring program also showed no significant difference in crawler activity levels between the upper and lower branches of crapemyrtle trees throughout the season (Vafaie et al., 2020). 

Mating behavior

Mating behavior was observed between adult males and adult females, which is an essential process required for reproduction. Newly emerged adult females typically remain mobile for a short period before settling down at a suitable location to feed on the plants. Thus, most adult females become sessile for the rest of the life cycle, while the alate adult male (once located the female) would initiate the mating process by taping the dorsal side of the female. Upon stimulation, the female reacts by lifting and retracting the rear end of her abdomen to accept copulation. The male then proceeds to curve its abdomen down and direct its genitalia to contact the ventral side of the female abdomen, where sperm transfer could be occurring (Figure7). After the mating process is completed, a reproductive female can be confirmed as the female develops its typical white ovisac structure (Figure 7). As a newly emerged adult female gaining its size, it might be undergoing development for sexual maturity as various adult preproduction periods were recorded. Therefore, depending on the female ages, it would take from 2 to 11 days before the development of ovisac could be observed. Shortly after the ovisac is developed (2-3 days), a female would start laying eggs, and the reproduction period can last up to 10 days.

Feeding behavior

As a sap-sucking insect, the feeding behavior of CMBS involves penetration of the plant epidermis and cortex tissues (using their mouthparts/stylets) to access the nutrient and water content in plant phloem and xylem. The Electrical Penetration Graph (EPG) technique enables the real-time monitoring of the insect's probing activities in plant tissues by analyzing the generated EPG waveforms. Five distinct EPG waveforms—C, potential drop, E1, E2, and G—have been identified for CMBS on the validated host plant, L. limii (Wu et al., 2022). Waveform C indicates the stylet pathway phase, during which the insect begins probing and carrying out extracellular stylet pathway activities. At this stage, sudden changes in voltages (potential drops) were observed, suggesting insects are actively puncturing living plant cells using stylets. Following the stylet pathway phase, the E and G waveforms signify successful access to the phloem and xylem, respectively, indicative of successful feeding activity. Consequently, the insect's difficulty or ease in accessing the phloem and xylem is correlated with the plant's resistance level to CMBS. This resistance level can be effectively assessed using the EPG technique, providing a valuable tool for evaluating a plant's susceptibility to CMBS infestation.

CMBS alternative hosts and feeding preference

Crapemyrtle bark scale has long been reported with a fairly wide host range. Online insect databases such as Scalenet has accumulated a good amount of host information for CMBS. However, recently, as the distribution of CMBS continues to expand beyond its native regions, more specifically in the United States, concerns have been raised regarding the expanded host range for CMBS beyond Lagerstroemia, and the potential threats that CMBS poses to the native and economic important plants in the United States.

To address these issues, several studies has been conducted on the feeding preference and host range of CMBS. Greenhouse trials confirmed quite a few species as CMBS hosts, which provided different/additional findings to the previous knowledge regarding CMBS hosts. Here is a summarization of the current knowledge on CMBS hosts.

Greenhouse trials

Multiple greenhouse trials were conducted between 2016 and 2020. All tested plants species were inoculated with CMBS-infested crapemyrtle twigs. CMBS infestation was identified as the presence of both male pupae and gravid female ovisacs during our experimental period, indicating the ability of CMBS to complete life cycle and reproduction on test plants.

For the economic plants in the United States, the infestations of CMBS were confirmed on apple (Malus domestica), Chaenomeles speciosa, Disopyros rhombifolia, Heimia salicifolia, Lagerstroemia ‘Spiced Plum’, M. angustifolia, and twelve out of thirty-five pomegranate cultivars. However, the levels of CMBS infestation on these test plant hosts in this study are very low compared to Lagerstroemia and may not cause significant damage. No sign of CMBS infestation was observed on Rubus ‘Arapaho’, R. ‘Navaho’, R. idaeus ‘Dorman Red’, R. fruticosus, Buxus microphylla var. koreana × B. sempervirens, B. harlandii, or D. virginiana in 2019. Although in a follow-up study with increased CMBS inoculation, one gravid female ovisac was observed on D. virginiana in 2020.

In this study, compared to crapemyrtle, all other species had very LOW number of scales, if any. For example, at its peak L. ‘Spiced Plum’ had 600 male pupae, Heimia had about 25 and all others had less than 10 (or even 5). Manuscript on this study ‘Feeding Preference of Crapemyrtle Bark Scale (Acanthococcus lagerstroemiae) on Different Species’ was published in June 2020 (https://www.mdpi.com/2075-4450/11/7/399).

Table 1 below summarized all our tested plants in four categories: Severe, Moderate, Minor, and None depending on the level of infestation recorded during our CMBS feeding experiments.

Table 1 Summarization of the crapemyrtle bark scale hosts with different levels of infestation.

X Levels of CMBS infestation were defined as: Severe (>100 female ovisacs per plant), Moderate (10-100 female ovisacs per plant), Minor (<10 female ovisacs per plant), and None (no CMBS pupae or ovisacs).

Y twelve out of thirty-five pomegranate cultivars were confirmed with minor CMBS infestation

Z need to be confirmed through DNA identification.

Host suitability among Lagerstroemia

The primary hosts of CMBS, as where CMBS got the common name from, are considered to be crapemyrtle or Lagerstroemia. However, other than the previously reported L. indica and L. fauriei, which are the most popular parentage of commercially available Lagerstroemia cultivars, the host suitability for CMBS among many other species in this genus remained unknown.

An independent study led by Bin Wu evaluated six Lagerstroemia species (L. caudata, L. fauriei ‘Kiowa’, L. indica ‘Dynamite’, L. limii, L. speciosa, and L. subcostata) and California loosestrife (Lythrum californicum) as CMBS hosts. Greenhouse experiment was conducted over a 25-week period and CMBS infestation were found on all tested plant species, although L. speciosa and Lythrum californicum had relatively low levels of infestation. For example, among the species with most severe infestations, L. limii had around 1000 male pupae and 600 female ovisacs, respectively, per plant at the peak of CMBS population. In contrast, L. speciosa had the highest around 45 male pupae and 57 female ovisacs, respectively.

The result suggests that the susceptibility towards CMBS differs among different Lagerstroemia species, and the species with low CMBS infestation, such as L. caudata and L. speciose may be utilized in the future breeding programs to develop CMBS resistant Lagerstroemia cultivars.

Host suitability among Callicarpa and Ficus Species

American Beautyberry, or Callicarpa americana, was one of the earlier alternative hosts reported for CMBS in the United States (Wang et al., 2016). The fact that Callicarpa americana is a native species in the US was worrisome, therefore, there was a need to evaluate the potential threat of CMBS to the genus of Callicarpa.

A greenhouse trials, also led by Bin Wu, confirmed CMBS infestation on nine Callicarpa species (C. acuminata, C. americana 'Bok Tower', C. bodinieri 'Profusion', C. dichotoma 'Issai', C. japonica var. luxurians, C. longissima 'Alba', C. pilosissima, C. randaiensis, and C. salicifolia) in 2019. Similar to all other species evaluated, the tested Callicarpa species can be categorized into three groups (severe, moderate, and minor) according to the level of CMBS infestation during the experiment. The most severe infestation recorded was on C. dichotoma 'Issai' (around 332 male pupae and 246 female ovisacs, respectively), while C. bodinieri 'Profusion' suffered the least (around 12 male pupae and 6 female ovisacs, respectively) from CMBS infestation. Unfortunately, none of all the Callicarpa evaluated was completely immune from CMBS attack.

Three Ficus species (F. pumila, F. roxburghii, and F. tikoua) were also evaluated in this study. No signs of CMBS infestation found on either F. pumila or F. roxburghii. F. tikoua had very minor CMBS infestation, which only 3 male pupae and 2 gravid female ovisacs per plant observed during the 25-week period in 2019.

Observation on soybean

Soybean, or Glycine max, was documented as one of the alternative hosts of CMBS in Asia. As an economically important agricultural crop in the United States, soybean generates over 40 billion in raw production value annually, and the United States continues to be one of the largest producers and exporters of soybean in the world (Hart, 2017). Therefore, it is reasonable to raise concern for the potential threat of CMBS to damage the soybean production in the United States.

Several greenhouse trials to evaluate the potential threat of CMBS to soybean. Although the presence of CMBS ovisac was observed on soybean plants under controlled environment, the infestation level is very LOW. Figure 8 shows the presence of active nymphs and opened female ovisac with visible pink eggs in it, as well as signs of black sooty mold accumulation, indicating CMBS feeding and reproducing on soybean.

Figure 8: nymphs and gravid females (opened ovisac with visible pink eggs) found on soybean plants (Glycine max) under controlled environment.

Observation in landscape and DNA identification

In 2018, an unknown scale infestation was first observed on Hypericum kalmianum (St. Johnswort) in a demonstration garden plot of Virginia Tech and the Virginia Agricultural Experiment Station in Virginia Beach, VA, USA. It was later confirmed by Schultz et al., through both morphological and molecular examinations, that this infestation on Hypericum was indeed caused by CMBS (Schultz, Szalanski, & Entomology, 2019). In 2020, a scale infestation observed on Spiraea japonica 'Shirobana' at University of Arkansas, has been confirmed as caused by CMBS through morphological and molecular identification (Xie et al., 2021).

Non-suitable hosts of CMBS

Several species or genus were determined as non-suitable hosts for CMBS, despite some of which has previously been documented as CMBS hosts. For example, no CMBS infestation on Myrtus communis or Ligustrum curvifolium in greenhoust trials. Although Buxus and Rubus were genus listed as CMBS hosts, no infestation has been observed under greenhouse condtions. It is possible that the previously reported CMBS hosts from these genera were varieties or cultivars naturally found or developed in the native region where CMBS was originally found.

Japanese Beetle (Popillia japonica)

The Japanese beetle (Popillia japonica Newman) (Scarabaeidae: Coleoptera), native to US, is present in most of states in the eastern US. It is a highly devastating pest, attacking a varieties of crape myrtle. Adults are shiny and attractive, medium sized, ovoid shaped beetles, about 0.5 inches in length, with metallic green colored bodies and iridescent bronze-colored elytra. The elytra do not cover the body completely, thus exposing 6 small tufts of white hair along the sides of the abdomen, under the wing edges. This is an important identifying character that distinguishes these beetles from other similar looking ones. Females are typically slightly larger than males. The adults are weak, clumsy fliers, often falling several times when they hit obstacles in their path.  However, they are known to travel long distances.

The beetles are first seen in late spring or early summer, feeding actively on foliage and flowers of various host plants.  The mature females lay eggs in clutches of 20-40, buried about 2-3 inches deep in the soil.  Eggs are variable in shape, from spheroidal to ellipsoidal or cylindrical, about 1/16 in long, and creamy white in color.  They hatch by mid-summer and the grubs feed on plant roots.  The grubs are stout and creamy white in color with a brown head and 3 pairs of legs, and are usually found in a curled position. The posterior part of the abdomen has a grayish or black tinge due to accumulation of fecal matter.  The full-grown grubs measure about 1 inch in length.  By late fall, the grubs dig deeper into the soil for the winter.  When the weather gets warmer, the grubs move back towards the surface and resume feeding on plant roots.  By late spring, they pupate in the soil.  The pupae are pale in color and resemble the adult, but the wings and appendages are folded closely to the body.  After 2 weeks, the adults emerge from the ground.  The complete life cycle takes about one year, and the beetles usually have one generation per year.

Asian Ambrosia Beetle (Xylosandrus crassiusculus)

Granulate ambrosia beetle (Xylosandrus crassiusculus (Mot.) is a serious pest of woody trees and shrubs including crape myrtle in the eastern US. This was previously known as the Asian ambrosia beetle. These tiny beetles were first detected in South Carolina in the 1970’s and have spread across the eastern US. Woody ornamental nursery plants and fruit trees are commonly affected. In spring or even in late winter (around mid-February), a large number of beetles can emerge and attack tree species, especially when they are young and stressed. The female beetles land on the bark of woody trees. Then, they bore through the inner bark and softwood of the tree, settling in the heartwood where they begin carving galleries.

Females of granulate ambrosia beetle commonly attack trunks of young nursery trees and woody shrubs, although mature trees under stress are also susceptible. They drill a network of tunnels within the heartwood where they lay eggs. Similar to other beetles, granulate ambrosia beetle has egg, larval, pupal and adult stages. Except for adults, all other stages occur only within the tree trunk. In the galleries, eggs, larval stages and pupae can occur together. Adults introduce symbiotic “ambrosia” fungi into the galleries as a food source for the developing larvae. Adults feed on the same fungi and remain along with their young until they mature and become adults. The female granulate ambrosia beetle is about 2.5 mm long. The young females mate with their male siblings within the galleries. Females can readily fly, whereas the males are flightless and do not emerge from the home gallery. Mated females leave the host trees seeking new trees to invade and lay eggs. They attack trees stressed by drought, flooding, mechanical wounding and but also trees that are apparently healthy. Typically, infestations are found below shoulder height on the tree.   

The biological regulation of crapemyrtle bark scale (CMBS) has been documented in both Asian and American contexts (Wang and Zhang 2014, Wang, Chen et al. 2016, Wang, Chen et al. 2016, Wu, Xie et al. 2022). In Asia, research has identified eight parasitoids from the Encyrtidae family, one parasitoid from the Aphelinidae family,  and six predators from the Coccinellidae and Chrysopidae families, all of which have been observed to play a role in mitigating CMBS infestations by significantly diminishing pest populations (Hayat, Alam et al. 1975, Zeya and Hayat 1993, Jiang and Xu 1998, Zhang and Huang 2001, Wang, Chen et al. 2016, Suh 2019). Concurrently, within the United States, a variety of coccinellids—namely Chilocorus spp., Harmonia axyridis, Hyperaspis bigeminata, and Hypersapis lateralis—have been detected actively preying on CMBS (Wang, Chen et al. 2016). Additionally, one green lacewing (Chrysoperla rufilabris) was confirmed preying on CMBS in the Texas U.S (Wu, Xie et al. 2022).

Classic biological control focusing on parasitoids;

(see details in Table National Integrated Pest Management (IPM) Database)

Conservative biological control:

To date, there is no documentation indicating the deployment of biological control agents for the conservative biological control of CMBS (Wang, Chen et al. 2016, Franco 2020, Wu, Xie et al. 2022). It is advisable to evaluate specialized parasitoids and predators for CMBS management, given their potential efficacy (Wang, Chen et al. 2016). Parasitoids with a more restricted host range are likely to have a lesser ecological impact compared to more generalist natural enemies. Furthermore, assessing the functional response of these parasitoids or predators to CMBS under quarantine conditions can provide invaluable insights for subsequent releases and large-scale propagation (Wang, Chen et al. 2016). An evaluative approach, employing before-and-after experimental design, can effectively measure the impacts of these parasitoids or predators. In essence, comprehensive assessments are critically needed to inform the development of IPM strategies tailored for the conservative biological control of CMBS.

Augmentation biological control:

In field observations, Chilocorus cacti, Hyperaspis bigeminata, Hyperaspis lateralis, and Chrysoperla rufilabris were identified as predators of CMBS. Subsequent laboratory studies confirmed their predatory roles upon CMBS (Wang, Chen et al. 2016, Wu, Xie et al. 2022). However, comprehensive data regarding the life history and voracity of these lady beetles remain to be elucidated to evaluate their potential for augmentative biological control of CMBS (Wang, Chen et al. 2016, Wang, Chen et al. 2016). Additionally, a thorough field investigation into the application of the Red-lipped green lacewing for augmentative biological control of CMBS is an imperative and promising avenue for research, aimed at determining the optimal timing for predator release (Wu, Xie et al. 2022).