Saturday, July 26, 2014

Pest News for Week of July 28th


From: Steve Frank, Extension Entomologist

Sycamore Lace Bugs Cause Yellow Leaves

This week I have gotten three samples from the Plant Disease and Insect Clinic with sycamore lace bug, Corythucha ciliata. I had just taken some pictures of these beautiful critters last week when I was in Asheville. They really do a number on sycamore leaves and this time of year heavily infested sycamores look pretty bad. The other lace bugs that are important landscape pests are the azalea lace bug and hawthorn lace bug. Like these, the sycamore lace bug causes stippling damage by piercing the underside of leaves with its stylet and sucking out the fluids. Large yellow and gray areas develop on the top of the leaves. In some cases, most leaves on a tree can be entirely covered in stippling damage.

Sycamore lace bugs are a native insect. They overwinter as adults under bark or in other sheltered spots and become active soon after bud break. They lay eggs in leaves and complete their lifecycle in around 30 days. However, research from China, where this is an invasive pest, shows that at high temperatures this happens much faster, even twice as fast. This suggests that it could be more abundant in hot urban areas where sycamores are often planted in parking lots and along roads. My anecdotal suggests this is true. Sycamores are wetland trees and probably are not very happy in hot, sunny, dry spots, but lace bugs clearly are.

Management of sycamore lace bugs will be similar as for other lace bugs, but you are typically dealing with large trees instead of small azalea bushes or cotoneaster. Thus systemic insecticides applied as a drench can be a good option. Applications of horticultural oil should also help keep abundance low just by killing adults and nymphs that are present.

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Sycamore lace bug nymphs. Photo: S. D. Frank.

Impatiens Necrotic Spot Virus

In the last month we have had several samples come into the Plant Disease and Insect Clinic with impatiens necrotic spot virus (INSV). These have primarily been greenhouse crops like impatiens and mums, but the virus can infect over 200 plant species. It is a lethal virus spread by thrips feeding. Managing INSV is critical because it can easily over run your crop and cause long-term problems. Thrips become infected with the virus while feeding as larvae. After they pupate, thrips spread the virus to new plants when they feed as adults.

Thus, INSV management starts with thrips management. The essence is to start with sanitation. Thrips can feed on hundreds of plants so any weeds growing in or near your greenhouse can support thrips feeding and egg laying. Get rid of pet plants and mother plants. Maybe you or your grandmother want to overwinter last year’s peppers or begonias, but do not do it. These can serve as reservoirs for thrips and virus and keep your house constantly infected.

If you have INSV in the greenhouse, get rid of all plants that show symptoms and consider getting rid of all plants that thrips have fed on. Plants do not immediately show symptoms, but they can still infect thrips. So even if you get rid of plants with visible spots thrips may continue to get infected and spread the virus. Get rid of thrips with insecticide applications or ramp up an existing biological control program to get thrips under control. Now is not the time to start a biological control program. Keep an eye out for tell tale rings and spots on leaves so you can keep ahead of this virus and of course monitor for thrips with sticky cards to keep ahead of them.

You can read more about thrips management in an Insect Note and recent article in GrowerTalks.

If you would like to see thrips defend themselves from predatory mites by butt slappin’ them watch the video here:

INSV on impatiens. Photo: Robert Wick, University of Massachusetts,

For more information contact your local Cooperative Extension Center and ask for the Commercial Horticulture Agent.