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One of the most common complaints from homeowners during the growing season is the appearance of a black, soot-like coating on leaves, stems, patios, vehicles, and outdoor furniture beneath landscape plants. While many assume this black growth is a plant disease, the real culprit is often an insect infestation. Sooty mold is a fungal growth that develops on honeydew, a sticky, sugar-rich waste product excreted by sap-feeding insects. Common honeydew-producing pests in Texas landscapes include aphids, whiteflies, scales, mealybugs, and psyllids. As these insects feed on plant sap, they remove more sugar than they can utilize and excrete the excess as honeydew. Sooty mold fungi then colonize this sticky residue, forming a dark coating on plant surfaces. The mold itself does not infect plant tissues or directly damage leaves. However, heavy accumulations can block sunlight and reduce photosynthesis, leading to decreased plant vigor and aesthetic quality. In severe cases, leaves may yellow, growth may slow, and plants can become stressed, particularly when combined with other environmental challenges. Several landscape plants are commonly affected by sooty mold in Texas, including crape myrtle, gardenia, holly, hibiscus, magnolia, citrus, and many ornamental trees and shrubs. Crape myrtle bark scale, for example, is a frequent cause of heavy honeydew production and subsequent sooty mold development on crape myrtles. Likewise, whiteflies and aphids often contribute to outbreaks on ornamentals and flowering plants. Successful management requires addressing the underlying insect problem rather than focusing solely on the mold. Begin by inspecting plants carefully, especially the undersides of leaves and stems, where many sap-feeding insects congregate. Look for live insects, cast skins, sticky honeydew, or ant activity. Ants are often attracted to honeydew and may indicate the presence of hidden pest populations. An integrated pest management (IPM) approach is the most effective strategy. Encourage natural enemies such as lady beetles, lacewings, parasitic wasps, and predatory bugs that help suppress aphids, scales, and whiteflies. Avoid unnecessary broad-spectrum insecticide applications that may disrupt beneficial insect populations. When pest numbers exceed acceptable levels, select insecticides based on the target pest and follow all label directions. Once the insect population is reduced, honeydew production will decline, and existing sooty mold will gradually weather away through rainfall, irrigation, and normal leaf growth. In some situations, washing leaves with water can improve appearance, but this will not solve the problem if the insects remain active. When blackened leaves appear in the landscape, remember that sooty mold is usually a symptom rather than the primary issue. Identifying and managing the honeydew-producing insects will provide the most effective long-term solution and help maintain healthy, attractive landscape plants throughout the season.
Figure: Sooty mold on crape myrtle leaves (A) caused by crape myrtle aphid (B), and sooty mold on crape myrtle stem/bark caused by crape myrtle bark scale (C)
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Texas has moved into summer earlier than usual, with high temperatures arriving well before the traditional peak season. While warm weather accelerates plant growth, it also creates ideal conditions for many insect and mite pests. For nursery growers, greenhouse producers, and landscape managers, early heat can mean earlier and more severe pest outbreaks. Many pests develop faster under high temperatures, allowing them to complete more generations in a shorter period. At the same time, heat and water stress can weaken plants, making them more susceptible to pest infestations. This combination often leads to increased pest pressure during early summer. Some of the most common pests to watch include spider mites, thrips, whiteflies, leafhoppers, and scale insects.
The best defense remains a strong Integrated Pest Management (IPM) program. Frequent scouting is critical during hot weather. Inspect plants regularly, especially new growth and leaf undersides, and use monitoring tools such as sticky cards or pheromone traps for early detection. In addition, minimizing plant stress through proper irrigation and balanced fertility can improve plant resilience. When treatments are necessary, rotate insecticides with different modes of action to help delay resistance development and preserve beneficial insects. Early detection and timely intervention are key. During hot summer weather, successful pest management starts with protecting plant health and staying proactive rather than reactive.  Rafia Khan, Ph. D.
Assistant Professor and Extension Specialist Texas A&M AgriLife Research and Extension Center, Overton, TX Excess rainfall during spring and summer can significantly increase pest pressure in nurseries, greenhouses, and landscapes. Warm temperatures combined with high humidity and prolonged moisture create favorable conditions for rapid pest development, survival, and spread. Soft-bodied insects such as aphids, whiteflies, thrips, and mites often become more active during wet weather periods. Excess moisture promotes lush plant growth and tender foliage, which are highly attractive to many pests. Standing water and saturated growing media can also encourage European pepper moth, fungus gnats and shore flies, particularly in greenhouse production systems. Wet conditions can make pest management more challenging. Rain may reduce the effectiveness of contact insecticides by washing away spray residues, often requiring repeated applications. Prolonged wet weather can also limit access to production areas, making routine scouting and timely pesticide applications difficult. High humidity and dense plant canopies further complicate early pest detection. Many pests, including thrips and mites, remain hidden within flowers, buds, or on the undersides of leaves, allowing populations to build unnoticed. In addition, storm events and strong winds may contribute to the movement and spread of invasive pests into new production areas. Excess rainfall may also disrupt beneficial insect activity. Natural enemies such as predators and parasitoids are often less active during prolonged storms and humid conditions, reducing natural pest suppression and allowing pest populations to increase rapidly once environmental conditions improve. Implementing proactive integrated pest management (IPM) practices is essential during periods of excessive rainfall. Regular scouting and monitoring with sticky traps can help detect pest populations early. Improving drainage, increasing air circulation, maintaining proper sanitation, avoiding overwatering, and removing heavily infested plant material can reduce favorable conditions for pests. Rotating insecticides with different modes of action and conserving beneficial insects are also important strategies for long-term pest management and resistance prevention. As weather patterns continue to become increasingly unpredictable, adopting management practices and maintaining consistent monitoring programs will remain Rafia Khan, Ph. D.
Assistant Professor and Extension Specialist Texas A&M AgriLife Research and Extension Center, Overton, TX Spring in Texas often brings warm temperatures along with frequent rain and storm events, creating highly favorable conditions for increased pest pressure in nurseries, greenhouses, and landscape systems. Elevated humidity and excess moisture significantly enhance pest development, survival, and reproduction, making this season particularly challenging for growers. These environmental conditions not only accelerate pest life cycles but also create ideal microhabitats for hidden and soil-associated pests, increasing the risk of sudden infestations and economic losses. Favorable Conditions for Pest OutbreaksSoft-bodied insects such as aphids, whiteflies, and thrips thrive under warm, humid conditions commonly observed during spring. The flush of new plant growth during this period provides tender, nutrient-rich tissues that are highly attractive for feeding and reproduction. As a result, pest populations can increase rapidly within a short period, often going unnoticed until visible damage appears. Without timely monitoring and intervention, these pests can quickly reach damaging levels and affect plant quality and marketability. Soil and Moisture Associated Pests Prolonged wet conditions create ideal environments for pests such as fungus gnats and shore flies, particularly in greenhouse and nursery production systems. Their larvae develop in moist growing media, feeding on organic matter and plant roots, which can weaken plants and reduce overall vigor. Additionally, pests like the European pepper moth benefit from high moisture conditions, as their larvae remain concealed in the lower canopy or within the growing media. This hidden feeding behavior, combined with favorable environmental conditions, makes early detection difficult and allows populations to build up before noticeable symptoms appear. Pest Spread and Increased Activity Rainfall and storm events can also contribute to the spread of pests within production systems. Splashing water can move infested soil, plant debris, eggs, and larvae between containers or across growing areas, facilitating rapid dispersal. Furthermore, outdoor pests such as caterpillars and beetles often become more active following rainfall, increasing feeding activity and the likelihood of damage. Wind and storm movement can also aid in dispersing adult insects into new areas, compounding pest pressure. Challenges in Pest Control Frequent rainfall presents additional challenges by reducing the effectiveness of insecticide applications. Rain can wash off residues from plant surfaces, shortening the duration of control and requiring more precise timing of applications. High humidity may also affect product performance and pest exposure, making control less consistent during extended wet periods. Take-Home Message Overall, rainy spring weather creates ideal conditions for pest outbreaks by enhancing survival, reproduction, and spread, while simultaneously reducing control effectiveness. Under these conditions, consistent scouting, proper irrigation management, and timely, integrated interventions are essential to minimize pest impact and maintain plant quality and marketability. Rafia Khan, Ph. D. Assistant Professor and Extension Specialist Texas A&M AgriLife Research and Extension Center, Overton, TX Rafia Khan, Ph. D. Texas A&M AgriLife Research and Extension Center Overton, TX. Spring is the most important production and sales season for Texas nurseries, and thoughtful preparation during late winter can significantly influence crop quality, pest pressure, and overall profitability. As temperatures begin to rise, the priority should be a thorough inspection of all overwintered plant material. Carefully examine plants for cold injury, root health issues, nutrient deficiencies, and early signs of insect or disease activity. Pests such as aphids, mites, whiteflies, and scale insects often establish tender new growth early in the season. Removing dead, damaged, or heavily infested plants reduces overwintering populations and minimizes the risk of rapid outbreaks once favorable conditions develop.
Equipment readiness is equally critical. Before spring applications begin, calibrate sprayers, fertilizer spreaders, and chemigation systems to ensure accurate delivery rates and uniform coverage. Check nozzles for wear, confirm pressure settings, and repair leaks. Proper calibration not only improves pest control efficacy but also prevents phytotoxicity, reduces product waste, and ensures compliance with label requirements. This is also a good time to review pesticide inventory and verify that products are properly stored and within expiration dates. Updating and reinforcing your Integrated Pest Management (IPM) program should be part of spring preparation. Establish a consistent scouting schedule and designate trained personnel responsible for monitoring crops. Use tools such as sticky cards, pheromone traps, and regular plant inspections to detect pest activity early. Accurate identification and threshold-based decision-making allow for targeted treatments and help prevent unnecessary applications. Early detection remains one of the most cost-effective pest management strategies in nursery production. Inspect irrigation systems before peak demand by checking drip lines, emitters, sprinklers, and pumps for leaks or uneven distribution, as poor irrigation can stress plants and increase susceptibility to disease and pests. Test growing media for pH and soluble salts, and ensure fertilization programs, especially controlled-release fertilizers, are properly applied to support healthy growth. Implement early weed control with uniform pre-emergent applications and winter weed removal to reduce competition and pest reservoirs. Provide staff with refresher training on scouting, safety, equipment use, and recordkeeping. A well-organized spring plan strengthens plant health, reduces pest pressure, and supports a successful nursery season. Rafia Khan, Ph.D. Assistant Professor and Extension Specialist Texas A&M AgriLife Research and Extension Center, Overton, TX Winter can feel like a break from pest pressure, but for nursery and greenhouse growers, many insects are still present and waiting for the right conditions. Protected structures, mild winter weather, and overwintering life stages allow many pests to survive on plants, in pots, in growing areas, in debris, and in weeds. If these pest populations are not addressed, they often resume early and aggressively in spring. Common winter pests include aphids, thrips, mealybugs, scale insects, whiteflies, spider mites, and greenhouse moth pests such as the European pepper moth. These insects can survive on plant material, in potting media, or within greenhouse structures, often going unnoticed until populations increase. Programmed scouting remains the foundation of winter Integrated Pest Management (IPM). Monitoring efforts should be focused on current in-house plants and newly arrived plant material. Inspect leaf undersides, stems, and growing points, and use sticky cards to detect flying insects early. Cultural practices play a key role in reducing pest pressure during winter. Sanitation, such as the removal of plant debris, leftover shipped plants, weeds, volunteer plants, and unused containers, should be removed from the production sites as they may harbor pests. Manage irrigation carefully to avoid conditions favorable for fungus gnats and root pests, and inspect incoming plants before placing them into production areas. When treatments are necessary, applying products strategically and rotating insecticide modes of action helps protect product performance and avoid costly resistance issues. Winter is also the best time for growers to step back and evaluate what worked and what didn’t during the past season. Reviewing pest records, adjusting management plans, and training employees to recognize early pest signs can pay off quickly. Investing time in winter pest management reduces carryover populations, improves plant quality, and helps operations enter spring with fewer surprises and lower control costs. Figure: Some greenhouse pests in winter. European pepper moth larva (A) and adult (B), Thrips (C), and mealybug (D) |
AuthorKim Cabrera, TNLA Marketing Manager Archives
August 2026
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