The usual suspects

Several years ago, Entomologist and Executive Director for the American Public Gardens Association Dr. Casey Sclar found that adult female mealybugs 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, as well as 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 and have confirmed Sclar’s observations in commercial greenhouses.

The calls I receive about indoor mealybug infestations here in the Northeast United States almost exclusively concern long-term production or maintenance (interiorscapes, conservatories) situations. There are three usual suspects.

Typical suspects
The citrus mealybug, the most common, has short waxy rods of roughly similar length around the body and one darker stripe (where wax is thinner) down the center of the back. It will produce some cottony egg masses as well.

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 more notorious 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 for more information at bit.ly/Z8U1Mh.

All about control
When it comes to controlling mealybugs, you must first assess why infestation persists in the first place 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 they 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. Growing ‘cool’ will also help slow the insects down. Of course, these may work for some plants or situations but not for others.

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 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 the citrus mealybug. We’re currently testing the soil mite Stratiolaelaps (formerly Hypoaspis) for mealybugs on or near roots. Be sure to consult with suppliers on release rates and frequency, as well as for selecting compatible insecticides if needed.

Insecticide update
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 may be as — or even more — important.

Labeled materials include Orthene/Acephate (certain plants only), TriStar, azadirachtin products (Azatin/Aza-Direct/Molt-X), pyrethroids (Decathlon, Tame, Astro, Talstar/generics), Talus, Duraguard, BotaniGard, Aria, horticultural oil (Suffoil-X, Ultra-Pure Oil, others), M-Pede and Enstar AQ. Safari, imidacloprid products (Marathon, Discus N/G, generics), Kontos and Flagship can be used as sprays or systemics. Including a spreading agent like Capsil or low rate of M-Pede may be helpful as well.

When it comes to fighting mealybug infestations, be sure to identify the culprit, pay close attention to sanitation, consider biological and nonchemical controls, and consult with an Extension specialist regarding insecticides that might work best. Rest assured, you’ll find an effective strategy that works as time goes by.

Daniel Gilrein is a frequent contributor to Greenhouse Management and an extension entomologist at Cornell University.