University of Maryland Extension

August Tree and Shrub Tips

fall webworm in a tree

(More tips from HGIC)

  • Fall webworm (photo above) is a late summer pest is a 1-2 inch long hairy caterpillar that creates large tent-like nests on the ends of branches of various shade trees and shrubs. It is unsightly but causes little damage. They can be left alone or knocked out of the tree with a broom, by a hard water spray, or pruning them out and disposing of them in the trash.
  • Numerous caterpillars, including leafrollers, orange striped oak worm, green-striped maple worms, oak skeletonizers, and sawflies are feeding on various shade trees. No controls are necessary unless feeding is severe. You may also see some large and unusual caterpillars with various colored spines and knobs that have been feeding in trees and are getting ready to pupate. These are mostly giant silk moths and should be left alone.
  • Bagworms are very noticeable and feeding on many trees and shrubs. They are usually not a problem on deciduous plants but should be controlled on evergreens. It is now too late to spray them with a biological control product. Where possible, remove bagworm bags from evergreen trees and shrubs, especially spruces. Throw them into a bag and place in the trash. Do not just drop them to the ground as they will crawl right back up the plant.
  • Lace bug feeding can be observed on azalea, hawthorn, rhododendron, serviceberry, oak, and sycamore. You’ll notice small white or yellow spots on the upper sides of leaves and small black fecal spots will appear on the undersides. They are more of a problem on stressed plants on exposed sunny sites.
  • The hemlock woolly adelgid is still very active on hemlocks in many landscapes. Adelgids are aphid-like sucking pests that appear as white, waxy masses. Heavy infestations can debilitate trees, particularly when they are stressed. Ultra-fine horticultural oil is a safe and effective insecticide to use but should not be applied if temperatures are expected to go above 85 -90 degrees F. Do not use on drought-stressed plants or during periods of very high humidity or the plants will experience leaf drop. Thorough coverage of the foliage is essential to achieving good control. A dormant oil spray in November through early March will also help to kill over-wintering adults. It is also possible to use a systemic insecticide registered for control of hemlock woolly adelgid. Apply as a drench around the base of the tree. Follow label instructions.
  • You may notice the browning of black locust leaves caused by locust leaf miner feeding. This is a perennial pest that does not debilitate the trees. Locust trees put out new growth throughout the growing season and are not adversely affected by the feeding damage.
  • August is frequently dry. If so, water deeply by allowing water to soak the soil directly underneath and around newly planted trees and shrubs. Check the depth of water penetration into the soil by digging a small hole after watering. Hard-crusted mulch will repel water and needs to be broken up with a rake or hoe to help the rain and irrigation water to penetrate the soil.
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