The usual suspects

Several years ago, entomologist and executive director for the American Public Gardens Association Dr. Casey Sclar found that adult mealybug females can live without a host plant an average of 10 to 19 days, and crawlers (newly hatched mealybugs) continue emerging up to 45 days after. For anyone who has battled mealybugs unsuccessfully – and you have company – this explains a lot.

Other reasons they’re difficult to control include a preference for protected, narrow or tight spaces where sprays don’t reach; high reproductive rates; a repellent waxy coating; and (we suspect) an ability to cope with systemic insecticides. Some species live on roots or part-time below ground. I have found them on fallen plant debris.

If you’re growing under cover, there are some usual suspects. The citrus mealybug, the most common, has short waxy rods of roughly similar length around the body and one darker stripe down the center of the back. It will produce some cottony egg masses.

The appropriately named longtailed mealybug has two sets of longish-white “tails” from the back end, but it produces no egg masses.

Particularly difficult to control, the Madeira mealybug looks like a prehistoric trilobite, bearing three rows of white waxy tufts down the back and a slightly greyish cast. It produces numerous cottony egg masses.

There are several other species, some of which are serious outdoor pests. Check Dr. Lance Osborne’s University of Florida website at http://mrec.ifas.ufl.edu/lso/mealybugs.htm for more information.
 

All about control

When it comes to controlling mealybugs you must first assess why infestation persists and tighten up on sanitation. In one case, a grower no longer reuses pots and power-washes infested benches between crops. Infested plants – those beyond rescue – are discarded, and new plants are inspected on arrival. Additionally, plants are spaced to improve spray coverage if insecticides are needed. Workers trained to detect infestations flag hotspots and avoid moving plants around.

Next, you must consider nonchemical controls. Sclar found that cooling plants for more than 36 hours at 36°F works, and researchers in Maryland showed hot (120°F) water treatment works as well.

Growers report good results with biological control, but constant monitoring is important. Releasing predatory lacewing eggs or larvae can be done almost any time. Cryptolaemus mealybug destroyer beetles are better in high mealybug populations and moderate-to-high temperatures (64°F to 91°F) and humidity (70 percent-plus). They reproduce only on mealybugs with egg masses and are less active during short winter days.

Leptomastix is a wasp parasitoid for citrus mealybug. We’re currently testing the soil mite Stratiolaelaps (formerly Hypoaspis) for mealybugs on or near roots. Consult with suppliers on release rates and frequency and for selecting compatible insecticides if needed.

I have experienced good, but sometimes mixed. results with insecticides. There is no question that coverage is critical, but mealybug species and choice of product is just as important.

Labeled materials include acephate (certain plants only), azadirachtin products, pyrethroids and horticultural oil. Imidacloprid products can be used as sprays or systemics.

Identify the culprit, pay close attention to sanitation, consider biological and nonchemical controls, and consult with an extension specialist on insecticides. You’ll find a strategy that works as time goes by.

Daniel Gilrein is an extension entomologist at Cornell University.