Damaged trees
Amy Jordan
Thursday, August 23, 2007
Bare and messy trees are apparent across Lyon County due to an assortment of gregarious insects. That’s the bad news; the good news is that the foliage damage or loss will not significantly hurt the trees and shrubs.
Leaves of some oak trees have turned brown due to feeding activity of the oak lace bug.
Though lace bugs are found on the bottom of leaves, the symptoms will become apparent on top. Damage appears as a stippling effect from white to yellow spots. From a distance, the oak leaves often appear bronze.
Even if you don’t find living specimens, their presence is given away by small, shiny dark spots of excrement on the undersides of leaves. Lace bugs normally do not cause significant damage to oaks, especially this late in the season. Control measures are not recommended.
Fall webworm is visible in landscapes and native timber across the state. The larvae feed in colonies in web-enclosed foliage. They begin by constructing small webs near the ends of branches and gradually increase the size of the web as the need for food increases.
Small trees may be completely defoliated by the larvae, but control with pesticide is not effective because of the protective webbing. Pruning and destroying the infested portions of branches is a common control practice while webs are still small, but is somewhat of an over-reaction.
A better approach is to simply comb out the webbing with a rake or pronged cultivator. Also, a stick or pole with a nail inserted crosswise can be used to snag individual webs if within reach. Twisting the pole after insertion will cause the web to wrap around the pole, then it can be removed and destroyed.
Bagworms are most apparent this time of year when they reach their mature size and do the most damage. Unfortunately at this point, pesticides are ineffective since feeding activity stops and they close off their bags.
Remove and destroy bags by hand or inspect plants next year and control them while they are still small. Bagworm hatch usually occurs in late May or early June, so insecticide applications made about a month later are most effective.
Yellow-necked caterpillars and their close relative, the walnut caterpillar can seem to strip a plant over night. When mature, both are about 2 inches in length and have long hairs along their body.
Skeletonization of lower leaf surfaces by small larvae generally goes unnoticed. Larger larvae consume all but leaf petioles.
Generally, by the time larvae are noticed, they have essentially completed their feeding phase, and insecticidal controls are considered to be of little value. Also, defoliation late in the season does not harm the health of the tree.