US National Arboretum


Pest Management

Pest Management Tips: August

image of a ladybug    Watch for tuliptree scale insects during August. Look for them on tulip poplars as well as magnolia and linden trees. If you see honeydew drip or sooty mold on leaves, suspect this scale. A heavy infestation can cause limb dieback, decline, and even death. They can be as large as a small pea, and range in color from gray to orange. The mobile, juvenile stage, called crawlers, hatch this month. Place a white sheet of paper under a branch and tap the foliage several times. Crawlers will be visible on the paper as dark dots. If the population is high, treat with horticultural oil or insecticidal soap later this month or next.

image of a ladybug     Fall webworms are also active this month. These caterpillars feed inside a silken tent at branch tips. These yellowish caterpillars are about an inch long and have black spots or stripes, with long hairs. They attack numerous trees and shrubs, including birch, cottonwood, sweetgum, fruit and nut trees, maples and willow. If the infestation is light, just prune out the webs. Heavier infections may require a spray treatment of Bacillus thuringienisis or the use of an insecticide containing spinosad. Thoroughly spray foliage around the webs, as these leaves will the caterpillars’ next meal.

image of a ladybug    Check your turf grass for the presence of Japanese beetle larvae. These grubs feed on grass roots. If your grass is looking less than vigorous, grab a handful of blades and pull. If the turf pulls up easily and does not have much root, suspect Japanese beetle larvae. Insecticides containing imidacloprid and formulated for grub control are available at garden centers and home improvement stores, and should be applied in August. A biological alternative is the nematode Heterorhabditis bacteriophora, which can be sprayed on the affected turf and then watered into the lawn. These nematodes invade the beetle larvae and release bacteria, which will kill the grub in 48 hours. Nematodes complete their life cycle within the grub and hundreds of thousands of young nematodes are released, in search of new grubs.

image of a ladybug    Summer can be a time of stress for many landscape plants. High heat and lack of rainfall can strain the health of many trees and shrubs. Immediate symptoms may be wilting, crispy leaves which drop prematurely. Many times root systems can be compromised and visible symptoms do not appear for months or years. 

Stressed plants are more susceptible to diseases and insect borers, which can invade the plant years after the initial weakening occurs. Canker diseases, indicated by lesions on the bark, will cause whole limbs to die; severe infections can kill individual trees and shrubs. Borer insects are attracted to stressed trees. Larval stages of moths and beetles feed inside the bark and wood, causing branches or whole trees to die. Control is difficult. If the feeding hole is found, an inserted wire may kill the larvae. Try using the beneficial nematode, Steinernema carpocapsae, to control borers. These nematodes can be sprayed on cracks in the bark during August. Remember the best control of canker diseases and insect borers is to avoid stressful conditions that weaken healthy trees. Thorough watering every week to ten days during times of heat and drought can prevent major pest problems in the future.

image of a ladybug    Bagworms, caterpillars that weave a small silky bag with leaf and stick pieces attached, have been actively feeding for some time now. By August, the bags can be over an inch long and can do considerable damage in a short time. They can strip a shrub or small tree completely of foliage in what seems like a couple of days. Pick the bags off as soon as you notice them or treat them with a spray containing spinosad. Bags will eventually reach 2” and if left to mature, male moths emerge from the bag later in the season, mating with females who never leave their bag. Each female can lay up to a thousand eggs, which remain in the bag until they hatch in the spring. It is a very good idea to remove and destroy bags any time of the year.

Pest Management Tips Home

The best way to manage pests is to use a combination of chemical and non-chemical control. Only take action when the problem is serious enough to damage the plant. If we all use Integrated Pest Management (IPM), we can control pests in an environmentally conscious manner.

 Back to the Arboretum Home Page
Arboretum Information || Events & Education || Gardens & Horticulture || Research Activities
Support the Arboretum || New Plant Introductions || USDA Plant Hardiness Zone Map || Comments
Search Our Site

Last Updated   June 11, 2009 2:59 PM