Keep it Green, by Michael Womack
Archives
| Arts & Entertainment
| Audio/Video
| Business
| Classifieds
| Columns
| Food
| Forums
| Health & Fitness
| News
| Obits
| Opinions
| People
| Politics
| Science/Technology
| Search
| Sports
| Subscribe
| Travel
| Weather
Saturday, June 16, 2001
Know which webworms are helpful
Many home gardeners are seeing fine webs on the bark of trees. This phenomenon is common this time of year, but don't worry. It's not a disease or an attack of tree killing insects or spiders. Although the unsightly webs are caused by an insect, they pose no danger to you or your trees. The critter you are encountering is actually a beneficial insect called barklice. Barklice is a member of the order Psocoptera, the same order as booklice, but they are not true lice.
Barklice occur on the trunks of trees where they feed on lichens, molds and fungi growing on the bark. They are a natural bark cleaning service. The species we see make unsightly silken webs on tree trunks and branches. The webs may completely wrap a tree's trunk to the tips of each branch. Underneath the protective webbing, barklice feed on the lichens and fungi. The most common host tree is oak and pecan, although any tree with lichen or fungal growth may be a temporary home to barklice.
Webs are most commonly found in July and August when conditions are favorable for insect development. Our unusually dry and hot June has contributed to their early appearance this year.
Barklice are harmless to trees and no insecticides are recommended for their control. Applying insecticides will not remove the webs. If a homeowner desires to remove the silken webs, all that is needed is a high-pressure water nozzle. If left undisturbed, the barklice will apparently remove the silken webs at the end of the summer once they have finished cleaning the bark.
Webs on the upper branches are another story. Fall webworms continue to attack many shade trees, particularly ash, pecan and mulberry trees during this time of year. They make unsightly web tents at the ends of branches, but even these pests won't do any long-term damage to your trees in most cases.
The actual "webworm" is the larval stage of a rather ordinary moth which is mostly white with dark spots on the wings. The pale yellow or green caterpillar is about 1 inch long when grown with a broad dusty stripe running down the back bordered on each side by a yellow stripe. It is also covered with tufts of long whitish hairs.
The newly hatched caterpillars begin feeding and spin webs over foliage in which they feed. Entire branches can be covered in webs and in severe infestations, the entire tree can be covered with several webs. The caterpillars eat the tender portions of the leaf, leaving the large veins and midrib. Only in the event of repeated severe defoliation will the tree be weakened enough to possibly die.
If webs become too numerous or are out of reach for pruning, then insecticides may be needed. One of the safest on the market are those containing Bacillus thuringiensis, a bacterial derivative that is effective only on caterpillars; it doesn't harm beneficial insects needed to keep other pest populations down. The toxins produced by the bacteria is ingested by the larvae and destroys the digestive tract of the caterpillar. The product, commonly called B.t. is marketed under the tradenames of Dipel, Thuricide, Bactur, or Bioworm. It is safe to use on most trees including fruit and nut trees.
You need to be aware that B.t. products are most effective on smaller caterpillars since it has to be ingested.
Other chemicals are available that are effective on caterpillars in later stages. The most common are carbamyl (Sevin) and malathion which are also labeled for use on fruit and nut crops.
Always remember to read the entire label and follow the directions of any chemical. That includes only treating the plants listed. Just remember, the label is the law, and it's there for your protection.
As you can see, there are a number of insects that could be attacking your trees and shrubs at this time of year. Knowing your problem will help you make the right decision as to whether to treat or not.
Michael Womack is a horticulturist with the Texas Agricultural Extension Service. Got a question? Michael Womack will answer landscape and gardening questions. Call 886-4648, category 3025 to record your question. Write Keep It Green, Corpus Christi Caller-Times, P.O. Box 9136, Corpus Christi, TX 78469 or email wm-womack@tamu.edu
2000 Caller-Times Publishing
Company, a Scripps Howard newspaper. All
rights reserved.
|
 |
 |
|
