Ground (Root) Mealybugs

Ground mealybugs (family Rhizoecidae) are soil-dwelling insects that suck and feed on basal stems and roots. They develop through three life stages. Eggs hatch into nymphs that grow through several increasingly larger instars before maturing into adults. Adults grow up to 1/16- to 3/16 inch long. Nymphs resemble small adults.

At least three, difficult-to-distinguish species of ground mealybugs feed on food and ornamental crops in California: ground mealybug (R. falcifer), Kondo mealybug (R. kondonis), and Trinity ground mealybug (R. bicirculus). Adults and nymphs are elongate and covered with a thin layer of powdery, white wax. They have distinct abdominal segments and lack the marginal wax filaments found on FOLIAR-FEEDING MEALYBUGS. In pots, ground mealybugs are concentrated on the outer portion of the rootball, between roots and the pot, but also occur throughout the root mass. The crawlers (mobile first instars) can occur on benches, containers, growing media, and anything that contacted infested plants, such as propagation tools and workers clothing and hands.

Adults can live 1 to 2 months. Adult females lay eggs in soil or give live birth to crawlers. Eggs usually hatch within 1 day of being laid. Crawlers disperse and are highly mobile, readily walking to infest nearby plants. One generation (egg to adult) at common soil temperatures requires about 2 to 4 months.

White, powdery wax on the soil surface especially near plant stems or around the root ball can indicate the presence of ground mealybugs. Slow (stunted) plant growth, pale to yellowish or wilted foliage that may drop prematurely, and an overall decline in healthy appearance of plants are common symptoms of ground mealybug infestations, although other maladies can also cause these symptoms.

Ground mealybugs commonly are introduced with new stock. Before moving new plants into production areas, remove a portion from their container and examine roots for white, powdery wax and the presence of slow-moving, oval, whitish insects. Similarly, inspect the roots of established plants if they appear to be declining. The presence of ants on plants or soil near basal stems can indicate that ground mealybugs or other phloem-feeding pests are present.

Rogue and discard infested plants, or effectively treat them with insecticide. Control ants, which can carry and spread the mealybugs among plants. Excellent sanitation practices, heat treatment, and soil-drench or systemic insecticides are the primary management methods.

Biological control has not been investigated.

Discard infested plants and those nearby which also are likely to be infested. It is difficult to completely disinfest roots of these soil-dwelling pests; starting fresh with pest-free plants and growing media and clean production areas can be preferable to the uncertainty of whether plants can be entirely disinfested and the risk that ground mealybugs will continue to spread and damage more plants.

Where infestations are discovered, sanitize (e.g., employ disinfectants, hot water, or steam) the benches, pots, tools, and other equipment used in that vicinity as these may be contaminated with crawlers. Use new or freshly pasteurized (e.g., heat-treated) growing media when propagating plants. Keep growing areas clean. Promptly remove crop debris and weeds and dispose of them in covered containers. Do not allow water (e.g., irrigation runoff) from areas infested with ground mealybugs to drain to areas believed free of these pests because mealybug crawlers are easily spread with moving water.

Heat treatment

Submerging pots containing plants in 120°F until the internal root ball temperature reaches 115°F entirely disinfests them of root mealybugs and does not significantly adversely affect the plants according to research with potted Rhapis palms in Hawaii. Aerated steam and hot water are highly effective in disinfesting mealybugs and numerous other pests from bulbs, corms, dormant stem cuttings, and tubers. First test small batches of each cultivar to determine control efficacy and plant tolerance to heat treatment before applying the method to large portions of the crop. A general recommendation for bulbs, corms, or rhizomes is to presoak them for 2 to 3 hours or overnight in 75°F water containing a wetting agent before immersing them in 111°F water for about 1-1/2 hours. Cool plant parts immediately afterward with clean, cold water, dry them thoroughly in warm air or sunshine, then store them under cool, low-humidity conditions until plants are used. See Control Pests by Heat Treatment of Plants in Nurseries for specific, heat-treatment guidelines by crop.

Controlling ants with sticky barriers, cultural controls especially pest-free stock, excellent sanitation, heat treatment, and botanical pyrethrins without piperonyl butoxide (PyGanic) are organically acceptable management methods.

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