Effective mealybug control strategies for greenhouse growers

Mealybugs infiltrate greenhouses as tiny first-instar crawlers, easily hitching a ride on plant structures, tools and worker clothing — making eradication a persistent challenge. No current strategy fully eliminates mealybugs, largely due to gaps in species identification and their resilience against control measures.

However, infestations can be managed at an optimal level through precise species identification and a strategic approach that considers overlooked factors and the efficacy of available insecticides.

Anatomy of mealybugs

Mealybugs are a type of scale insect belonging to the family Pseudococcidae. These insects are small, slow-moving, oval-shaped and covered with white, cottony wax. Most mealybug species are white, off-white or light gray, but some may be yellow, pink or orange in color.

Eggs, crawlers and adults may coexist in dense colonies. Females lay eggs in clusters, except for some species like long-tailed mealybugs, which produce live young (crawlers). The egg mass is typically yellow to orange and is covered by a cottony secretion, giving it a wool-like appearance. Adult females resemble nymphs but are larger in size. Males are usually smaller than females, have two pairs of wings and are short-lived, as they do not feed.

Nymphs, which are smaller than adults, go through three to four nymphal instars for females and four to five for males. The nymphal stage generally has shorter marginal filaments compared to adults. The mouthparts of all mealybugs are hair-like structures, clearly visible under a microscope.

The persistent pest

Mealybugs are significant insect pests in greenhouse, nursery, landscape and interiorscape environments. They feed on a wide variety of plants, including annuals, perennials, shrubs, palms, grasses, trees, fruits, vegetables and herbs. Different mealybug species have varying host ranges, making them difficult to control using insecticides.

Several studies have highlighted additional reasons for this challenge. The waxy layer around their bodies protects them from pesticide exposure. In some cases, they can easily hide in sheltered areas of the plant, such as under leaves or in the trunk. Foliar spray applications may not cover all areas, and the drenching method is not always 100% effective. Due to their small size, mealybugs may not ingest enough pesticide to be lethal.

Dense colonies also complicate control efforts, as the top layer may not feed. Eggs, crawlers and adults coexist in colonies, with eggs hatching throughout the season. This necessitates repeated insecticide applications when necessary.

Nearly all plant species found in nurseries can host at least one mealybug species. In greenhouses, the predominant species are citrus mealybugs (Planococcus citri) and Madeira mealybugs (Phenacoccus madeirensis). Most experiments on insecticide efficacy have been conducted on these species.

However, there is limited evidence of efficacy against other species, such as the Mexican mealybug (Phenacoccus gossypii), striped mealybug (Ferrisia virgata), Phormium mealybug (Balanococcus diminutus) and root mealybugs (Ripersiella hibisci and Rhizoecus species). Managing mealybugs has become a major concern for growers due to the difficulty of identification and control with currently available insecticides.

Mealybug management

Mealybug infestation can be effectively managed by adopting a strategic approach that considers the following factors:

Accurate species diagnostics: Mealybugs’ susceptibility to chemical control varies across life stages due to key adaptations. Early instars evade exposure by hiding, while later instars develop a wax coating that blocks insecticides. Their irregular feeding also prevents toxin buildup.

Since each species progresses through life stages at different rates, timing treatments effectively is challenging. Accurate species identification using both morphological and molecular methods is essential for targeting the most vulnerable stages with properly timed chemical applications.

Although only a handful of species are reported in U.S. greenhouses, we recommend confirming the species and studying its biology — particularly its life cycle duration and number of generations per year — to optimize chemical control strategies.

Mode of action: Prolonged use of a single insecticide can lead to resistance in mealybugs. Rotating insecticides with different modes of action is essential to mitigate resistance development.

Number of sprays per season: Some pesticide labels specify the maximum number of sprays per season, such as one for Altus; two for TriStar 8.5 SL, Distance, Talus and Akari; and four for XXpire and Hachi-Hachi. Many pesticides labeled for mealybug control in greenhouses do not mention spray limits. Labels should be carefully reviewed.

Restricted Entry Interval (REI): The REI should be a key consideration when selecting insecticides. For example, Orthene TTO has a REI of 24 hours, while Flagship 25 WP has an REI of 12 hours. Although Orthene TTO may offer better efficacy, the shorter REI of Flagship 25 WP might make it a more practical choice in certain scenarios.

Coverage and residual effect: For immediate control with assured coverage, pesticides such as horticultural oil, pyrethroids and acephate can be effective. In cases where pests are hidden and a residual effect is desired, systemic insecticides like dinotefuran (from the neonicotinoid group) or flupyradifurone (from the butenolide group) are recommended. Combining systemic and contact insecticides on a rotational basis can enhance control and reduce resistance development.

Waxy coating on mealybug bodies: Research indicates that early instars or crawlers have less waxy covering than adults, making them more susceptible to insecticides. Systemic or translaminar insecticides are recommended for better penetration. Proper identification of the mealybug’s life stage is crucial.

Mealybug species: The efficacy of insecticides varies by species. For instance, Ventigra can control approximately 77.5% of citrus mealybugs but is more effective against Madeira mealybugs, with a control rate of about 97.5.

Efficacy limitations of systemic insecticides: Research has shown that systemic insecticides are not sufficiently effective in controlling citrus mealybugs in greenhouse environments. Contact applications may yield better results in such cases.

Important notes

Available insecticide efficacies: On pages 94-95, we summarize efficacy data from the 2023 IR-4 Ornamental Horticulture Program Database. Tailored recommendations for selecting insecticides on a rotational basis, based on the above factors, are provided to address control measures for different mealybug species. The data are obtained from the 2023 IR-4 Ornamental Horticulture Program Database. All efficacy rates were observed after two sprays applied at a 14-day interval. For Acephate, Orthene TTO, DuraGuard ME and Kontos, the REI is 24 hours, while for AzaGuard, Suffoil-X and Ultra-Pure TM Oil, it is only four hours. For all other mentioned insecticides, the REI is 12 hours.

Aria 50SG, Bountify, Chlorpyrifos 2.32%, Flagship 0.22G, Fulcrum, Natural Solutions - V. Lecanii, Orthene 75S, Preclude TR, Safari 2G, Sarisa 50SL, Talstar NF, Talus 40SC, Talus WP, TriStar 30SG, TriStar 70WSP and V-10433 are listed in the IR-4 sheet but are no longer registered.

A16901B 45WG, Bountify, BW 133, BW 238 ES, BW 238 WP, BW 279 N, ISM-555, KOC22018-8, MBI 203 SC2, MBI 205, NI02ES-1, QRD 400 (also known as Facin), RTSA 721 and SP3014 are not registered for the production of environmental horticulture crops.

Acelypryn, Mainspring GNL 200SC, Merit 75 WP, Mesurol 75-W, TetraCURB Concentrate, TetraCURB Max, TetraCURB Organic, TriStar 30SG, TriStar 70WSP and Velifer are registered products listed in the IR-4 sheet. However, their labels do not specify their use for controlling mealybugs.

Safari 20SG insecticide is used for controlling five species of mealybugs. It showed its efficacy at over 90% and in some cases 100%, and its REI is 12 hours.

On the other hand, Orthene TTO is used for controlling four species of mealybugs (citrus, Madeira, Mexican and root) with greater than 90% efficacy, a 24-hour REI and different mode of action than Safari 20SG.

Flagship 25 WG is also used for controlling four species of mealybugs (citrus, Madeira, Mexican and Phormium), with more than 90% efficacy, except one species, which is below the rate with a 12-hour REI. The mode of action for Flagship 25 WG is like Safari 20SG, which is nicotinic acetylcholine receptor agonist.

So, Safari 20SG is the best insecticide that could be used in the management of different species of mealybugs in greenhouses. If Safari is not available, Orthene TTO or Flagship 25 WG could be used, as they have good to excellent efficacy in population reduction. Distance, Ventigra, Kontos and Aria also have the potential to kill such pests at an acceptable rate.

Zee Ahmed, Ph.D., an assistant professor at Clemson University, welcomed two Ph.D. students, Powlomee Mondal and Peilin Tan, to his Turf and Ornamental Lab. Their research focuses on diagnostic tools and control strategies for managing mealybugs in greenhouses.