EXPERT TREE CARE

Fall Webworm

It is not difficult to spot the ugly nests of the Fall Webworm this time of year. The fall webworm is a native pest of trees and shrubs. It makes its appearance in late summer to early fall, and attacks predominantly hickory, walnut, birch, cherry and crabapple trees.

Fall Webworm constructs its nest over the end of branches, consisting of a silk web over the affected leaves. The web expands to include more leaves as the enclosed leaves are consumed. Webs can eventually contain 2-3 feet of a branch. The web is similar to that of the eastern tent caterpillar we dealt with in early spring, except the latter builds its web at the crotch section of branches, while the fall webworm infests the end of branches.
The fall webworm feeds mainly on leaf tissue between the veins which results in leaves having a “skeletonized” appearance.

Fall Webworm over-winters in the pupae stage on or in the soil. Eggs are laid by female moths late in June through July. Hatching will occur during July and the young caterpillars will immediately begin building their silken web. The web protects them from predators.

Since the infestation and feeding occurs late in the season, tree leaves normally have already photosynthesized to make food during the summer and have stored the energy needed for survival and growth. However, this season, many leaves were lost early in the growing season due to late frosts and freezes. Trees had to use food reserves to push out their secondary leaves. In addition, drought has caused tremendous stress on trees. Repeated stress on the same tree can cause a mortality spiral of which a tree never fully recovers. If your trees have suffered other stressors this season, you may want to manage this pest.

• If infestation is limited to accessible branches, pruning and destroying branches that contain nests and caterpillars is effective.

• Piercing or cutting the web, will expose the webworm to larval parasites and many predators such as yellow jackets, wasps (which are carnivores), birds, predatory stink bugs and parasitic flies.

• Our arborists can spray a bio-rational (environmentally friendly) pesticide to kill caterpillars under ½ an inch. This spray will not harm the beneficial predators of the webworm or animals visiting the tree. If caterpillars are larger, we may use a different mode of management.

• Do not attempt to burn the nests of these caterpillars. Burning damages bark and the vascular system under the bark. This can seriously harm the tree.

The Effects of Drought

This past season has been one of the driest seasons on record. This stress, compiled with very high temperatures has caused sometimes irreversible damage to our trees.
Water is the most limiting resource for tree and plant growth. Water is necessary for nearly all biological and biochemical processes within plant cells. Water is also necessary for uptake and transport of nutrients. When soil moisture is deficient, trees react by allocating energy differently. When water is limited to the point of plant tissue or biological process damage, trees will begin to decline, sometimes to the point of death. Resistance to insects and disease is also reduced or lost when moisture is deficient. Our arborists know that come next season, we will be seeing more of diseases such as cankers, vascular wilts, and root rots. Insects, particularly wood borers will also take advantage of our water-stressed trees. Many drought-stressed plants also show increased sensitivity to de-icing salts, air pollutants, and pesticides. In many situations, flower production will be limited on flowering trees.

Some signs of drought stress are;

• Curling, mottled, or browning of the edges of leaves
• Smaller than normal leaves
• Leaf drop
• Pre-mature fall color
• Twig and branch die-back
• Bark cracks

Trees growing in native soils and environments usually adapt better to drought situations than trees we plant in our landscapes. There are several reasons for this some of which are: poor species choices, planting in the wrong site, planting too deeply, mulching too thickly, or leaving burlap and/or ties on the rootball.
These situations cause root hairs (the fine absorbing part of the root) to die. When we finally do get rain, the roots can’t take advantage of it.
• Supplemental watering of trees can be timed to help trees recover water and minimize pest problems on surrounding plants. Water to the equivalent of 5 gallons per inch of trunk diameter, weekly. Evergreens need to go into winter with an ample supply of moisture.

• If you have an automated irrigation system, set the timer to go off in the very early hours of the morning (pre-dawn). This will minimize evaporation in addition to minimizing disease caused by prolonged wetness on leaves.
• If hand-watering, invest in a water wand or other shower-soaker type nozzle. This will allow you to direct water beneath the plant to soak the soil and avoid wetting the leaves, especially if the only available time you can water is in the evening.
• The use of organic mulch such as wood chips (without landscape fabric barriers on the soil) is the healthiest practice for plants. Mulch keeps roots cool, suppresses weeds and conserves soil moisture.

Our certified arborists are available to assist you with any tree or landscape related problem.

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