Webs in your trees

By Steve Roark | The Winchester Sun

You may have noticed trees with end branch­es cov­ered with a gaum of spi­dery web­bing. The cause is a pesky lit­tle cater­pil­lar called Fall Webworm, whose pop­u­la­tion seems to be up this year.

Seems like when­ev­er I write about a tree pest it involves a for­eign invad­er that got loose on us. But fall web­worm (Hyphantria cunea) is actu­al­ly a native species that shows up this time of year. The sim­plest way to describe them is to go through their life cycle.

The lar­val cater­pil­lars are the eat­ing machine stage that hatch out in mid-sum­mer from eggs the females laid on the under­side of leaves. They are pale yel­low with an orange head and are cov­ered with long whitish hairs that occur in tufts. They start off small but end up being around an inch or so long at maturity.

Soon after they hatch the lar­vae spin a silken web over foliage they want to eat, typ­i­cal­ly at the end branch­es, which pro­tects them from preda­tors. As they grow larg­er, they expand the web tent to enclose more leaves, which can even­tu­al­ly be up to two or three feet long. The type of feed­ing they do is called skele­toniza­tion, where they eat every­thing but the veins, leav­ing behind a leaf skeleton.

The lar­vae mature about six weeks after hatch­ing, when they will drop to the ground and pupate in the soil to over­win­ter. They emerge in ear­ly sum­mer as medi­um-sized white moths, which mate and start the cycle of life over.

The worms feed on most hard­wood trees, and are par­tial to hick­o­ry, oak, wal­nut, red­bud, cher­ry, and crabap­ple. While they can defo­li­ate a small tree, they rarely kill it. Larger trees are nor­mal­ly unharmed by what lit­tle dam­age they do to them, and the prob­lem is cos­met­ic rather than health: a web tent full of leaf skele­tons and bug poop is unsightly.

So, if you have these guys eat­ing on your tree, there are a cou­ple of options to con­trol them. If you can reach them, sim­ply cut off the branch above the web and destroy it. This would best be done ear­ly enough so that the lar­vae don’t mature and have a chance to pupate. Garden insec­ti­cides will kill them (always check the label), but it’s best to catch the worms and the web ear­ly while they’re small. The larg­er web tents will like­ly be too thick for sprays to penetrate.

You may con­fuse fall web­worm with a sim­i­lar pest called east­ern tent cater­pil­lar, which also does the pro­tec­tive web tent thing. But the east­ern tent is a spring­time prob­lem, and their tent is formed at branch crotch­es rather than branch ends.