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All About Webworms
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 Joe Lamp'l - DIY Network
Every year in late summer, I start seeing masses of silky webs engulfing the tips of tree branches all around town. They almost look like puffy white clouds. Chances are you are seeing them too since they're native to North America and Mexico and found throughout the United States and Canada. Not sure what they are? They're fall webworms.
Many people confuse these with a similar sight in the spring, typically in the crotches of trees. They are the eastern tent caterpillar. If you cannot seem to remember which is which, here's how to never be confused again; yes, fall webworms appear mostly in the "fall" but they always looks like they could 'fall' out of the trees since they're found on the tips of the branches. Tent caterpillars on the other hand, (spring to early summer) build 'tents' in the crotches of the trees, which is the best place to pitch a tent if you were doing so in a tree! The fall webworm (Hyphantria cunea) is the larval form of the tiger moth. Cocoons over-winter in leaf debris and mulch and the adult moth appears in May to July. She lays 200 to 500 eggs underneath the leaves of deciduous trees in late spring through fall. In much of the United States, there are two generations, although there can be up to four in a single year.
This first generation is small and generally goes unnoticed. The eggs hatch in a few days and the larvae begin spinning webs around the leaves as they eat. They never leave the protection of the web while they are eating and growing. Once they have had their fill, by mid-summer, they form cocoons in the bark of trees and in ground debris and the cycle continues. The second generation is the one we notice about now. It is more obvious, larger and more destructive. The caterpillars are yellowish to greenish, covered with long silky gray hairs, with a dusky stripe down the back and a yellow stripe on either side. They may have either a black or red head. Full-grown larvae can eventually reach an inch in length.
Fall webworms feed on about 100 different species of deciduous trees but rarely on conifers. In the east, trees that are targeted include: pecan, walnut, American elm, hickory, fruit trees and some maples. In western areas, alder, willow, cottonwood and fruit trees are favorites. Shade trees and ornamentals can be heavily defoliated. However, in most cases, this defoliation will not materially damage the trees since they will lose their leaves in just a matter of weeks anyway.
Only in severe cases is the infestation so bad the tree cannot recover. But, in the case of pecan and fruit trees, the leaves are more critical for fruit production and the ripening fruit can become bound up in the webs, potentially reducing the yield.
Homeowners can have some control over populations of fall webworms. A thorough late fall or early spring cleanup of leaf litter and mulch will help eliminate many of the over-wintering cocoons. However, once the inevitable webs occur again in late summer, you can simply open them up with a broom or other long handled object that exposes the larvae to birds so nature can take its course. If you desire a more proactive approach, a spray or dusting of Bt (Bacillus thuringiensis and often sold as 'Dipel') is a biological, organic pesticide that is target specific. In order for effective penetration, the web must be opened.
While not harmful to wildlife, bees or humans, the pesticide can kill other caterpillars and beneficial butterfly larvae. As with any pest control application, please use with caution and discretion.
But, in the case of webworms and many other 'pests', I do nothing when it comes to pest control intervention, opting for a bit of 'extra tolerance' over aesthetics. It's my way of picking my battles and taking a more eco-friendly approach. Besides, I enjoy the visual reminder that fall is on the way.
For more images related to this article, visit www.joegardener.com/pests and look for the article on fall webworms.
(Joe Lamp'l, host of Fresh from the Garden on the DIY Network and GardenSMART on PBS, is a Master Gardener and author. For more information visit www.joegardener.com and www.DIYnetwork.com. Or visit scrippsnews.com) |
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