Questions From The Plant Clinic: Mealybugs
Master Gardener Volunteer Diane Forrest discovered that battling mealybugs can be a difficult task here in Florida. Read all about what she learned while putting into practice University of Florida suggestions for controlling these garden pests!
The Mealybug Apocalypse
Our Florida spring was a wonderful time for planting and growing, with soaking rains and plenty of sun. But as it was perfect for plants, it became very clear that it was perfect for pest infestations too. A robust school native plant and pollinator flower garden was suddenly taken down by a massive attack of mealybugs. Mealybugs like nitrogen so the beautiful profusion of plant growth not only was an ideal feeding environment for them but also provided their perfect cover for hiding and breeding. After experiencing this “bug-apocalypse”, I wanted to learn more about them in hopes of helping fellow gardeners & future gardens fend off this damaging pest.
A few mealybug (MBs) stats…
- MBs have pierce-sucking mouth parts feeding on underside of leaves, tucked in stem axils and at base of plants
- Their feeding injects toxic saliva into plants stunting plant growth, causing leaf yellowing and distortion and eventual death of plant.
- Adults have waxy coatings and produce a white cottony appearance on plants to protect them and their young from elements and controlling sprays
- Adult females are wingless, can live up to 3-4 weeks, laying 30 eggs/day in a cotton like sac coating; they can lay 300-600 eggs over their lifetime & die once done laying eggs.
- Eggs are oval, light yellow & hatch in 5-10 days but can remain in sacs during unfavorable conditions
- Young nymphs “crawlers” crawl until they settle in plants; nymphs mature in 6-10 weeks; male nymphs can have a cottony cocoon
- Adult males are winged, don’t have mouthparts and are short lived; existing only to fertilize females. Adult males can fly to plants to find wingless female adults.
- MBS are found in plant crevices & cracks including stem axils, underside of leaves, where fruits touch one another & even under tapes, inside staking materials like bamboo, on pot edges, garden bordering materials and benches.
- MBs secrete honeydew, a host for sooty mold. Ants harvest honeydew and will protect MBs to assist in honey dew production, moving them around plants.
Florida has many types of MB species & some even feed on plant roots, developing slowly over 3-6 months, making them hard to detect until a plant is severely infested. Two common types are described below. You can read more about MB types via link to Univ of FL’s Dr. Lance Osborne in footnotes below.
Citrus MBs have a single stripe down their back and feed on citrus, stunting growth & yellowing leaves. Their honeydew promotes sooty mold, a common citrus problem. Their feeding can cause fruit drop or lumpy fruit. Most commonly found during spring & summer, they peak in June & July. Rainy and warm weather assists in population decline. Citrus MBs affect many ornamentals as well.
Long tailed MBs feed on tropical fruits & ornamentals. Differences from the citrus MB is that is has two long, waxy string-like tails and nymphs hatch immediately upon egg laying. Both male & female nymphs develop the cottony protective coat.
Controlling MBs is difficult and a relatively thankless task in the garden, especially with heavy infestation. Mealy bugs can be brought home on new plant purchases, so inspect your plants before you buy. Keep a good eye on your fruits, vegetables, herbs and ornamentals and deal with a MB infestation quickly. Unfortunately, disposal of heavily infested plants is best. Sanitation is critical too. Check for them both inside and outside of container walls, benches, tools, plant debris and mulch.
If an infested plant is in a container, dispose of all soil and thoroughly clean the pot before reuse. Disposal means tying all infected material in bag, careful not to let bugs drop off into garden soil or mulch and place the bag in a lidded container for yard waste pick up. High nitrogen fertilizers can promote the attraction of MBs so use them carefully in your landscape, if at all.
Natural predators include several ladybird beetles species, the best known aptly named “mealybug destroyer;” several parasitic wasps, green and brown lacewings, trash bugs and scale eating caterpillars.
Insecticidal soap can assist in killing crawlers, especially before they’ve developed their waxy coat to protect them. Several applications will be necessary as new hatches occur. Chemical sprays are available but not highly recommended. They can be very harmful to beneficial insects feeding on plants. There are also studies finding MBs become resistant to chemical treatment over time. For mature MBs, a forceful water spray can knock them off plants, where they can be destroyed or treated with spray. Remember their waxy coating is there to protect so direct contact is required and may not always work.
My Method for Controlling Mealybugs
In my own garden, several of my herbs and ornamentals, sage and salvias are MB favorites, and my African Blue Basil plant, a pollinator favorite, became severely infected. Their white waxy coatings looked just like the new flower buds on the bracts. I developed my own “squish, drop and spray” technique, not officially endorsed by scientific expertise, but it seems to be working so far.
Remove as many MBs and eggs by gently pulling infected stems and flower bracts over a bucket of soapy water so they drop into water. If your plant has stems and leaves too infected to save, trim them off, letting them fall directly into the bucket or a waste bag. Finally spray the plant with horticultural soap, be sure & test on just a few leaves of the plant to make sure spray doesn’t burn it, applying in early morning or evening.
Swish your bucket of water to make sure MBS get good dose of water and let it sit in the sun for a day or two to get nice and hot. (See footnote below for interesting information on pests and hot water treatment from University of Hawaii.) You’ll have a slimy looking brew, but once all MBs have perished in water, it can be drained elsewhere in your yard. Then inspect your garden and plants frequently and repeat, repeat, repeat!
Lance S. Osborne, Prof. of Entomology, University of Florida; https://mrec.ifas.ufl.edu/lso/mealybugs.htm
Universtity of Conneticut College of Agriculture, Health and Natural Resources
Univ. of California Nursery & Floraculture Alliance, Division of UC’s Dept of Agriculture & Natural Resources
Dr. Arnold Hara, Professor of Entomology, Department of Plant and Environmental Protection Sciences at the University of Hawaii in Manoa; http://ucnfanews.ucanr.edu/Articles/Regional_Report_San_Diego_and_Riverside_Counties/Spring_2013__Hot_Water_Treatments_to_Control_Pests/
“Dr. Hara has tested a hot water bath method on a number of plant species and found that immersion at 120.3°F for 1 to 10 minutes gave effective control of several species of insects, including aphids, scale, mealybugs and mites on nursery cuttings. Although the root mealybug is a very difficult to control or eliminate, hot water dips are as effective as insecticides against this pest. Experiments showed that submerging potted rhapis palms in water held at 120°F until the internal root ball temperature reached 115°F was 100 percent effective in killing root mealybugs. Heat damage to plants was reduced or eliminated by following the hot water shower with 1 to 2 minutes of cool water. Orchids and bromeliads were the only plants tested that were sensitive to the treatment.”