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December 20, 2014

Webworms look creepy, but cause little harm to trees

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Posted: Sunday, July 6, 2014 12:32 am

Look, up in the trees! Are those alien pods bent on taking over the planet? No, those big silky nests filled with wiggling caterpillars are actually fall webworms, and though they look creepy, they cause little damage to the trees, according to an Alabama Cooperative Extension System horticulturist.

“They hurt the looks more than anything else, but as far as damage, it’s not that big of a deal,” said Chip East, ACES regional extension agent for the Piedmont region, which includes Talladega County.

“There are some insecticides we can spray on that, but you can’t spray a whole pecan tree. You can spray a small tree or plant to suppress the growth, but generally speaking, as far as the health of the tree, it’s not that big a deal.”

East suggests cutting the tip of the branch that contains the webworm and disposing of it worms and all. He recommends against setting the nests on fire, at the risk of fire spreading and damaging the tree.

Fall webworms shouldn’t be confused with bagworms, pests that grow in much smaller bags. According to an ACES publication, “bagworms are serious pests of ornamental evergreens in Alabama. Their spindle-shaped bags made of silk and portions of foliage and twigs may go unnoticed until serious damage occurs to the plant.”

East said gardeners now noticing bagworms on their junipers or Leyland cypress have had them for several years. “They didn’t just come in this year. They go undetected. We pick them off by hand and throw them away, but when you’ve got thousands of them, it presents a problem.”

While those two kinds of worms can be an unsightly nuisance, East said there are several pests that are much nastier that gardeners in central Alabama should look out for.

“Ambrosia beetles are bad,” East said. “They bore into the bark of a tree and the adult lays eggs. In the larval stage they can crawl into the trunk of the tree and chew the wood up. You’ll see their excrement and sawdust looking like straws sticking out of holes in the trees.”

An infestation of ambrosia beetles can kill a variety of trees, East said.

“My main job is to work with commercial horticulture producers – sod farms, Christmas tree farms and fruit and vegetable growers. I’ve got insect traps that we check regularly,” he said.

East uses baits ranging from cider vinegar to insect pheromones to sugar water mixed with yeast to attract bugs to his traps so he can tell farmers and gardeners what types of insects they’re dealing with and how to get rid of the ones that cause damage.

“Fall army worms are bad on tomatoes, but they’re also bad on hayfields,” he said. “You can have a hayfield ready to be cut, and in two to three days the army worms can have it looking like bare ground. That’s a few thousand dollars out of a farmer’s pocket. We’ve already seen some of those this year,” he said.

Beginning around the Fourth of July, those are some bugs to check on, East said.

“Right now we’re checking for spotted-wing drosophila. It’s a little fruit fly. A lot of flies feed on over-ripe fruit, which doesn’t matter to people because that’s not what we eat. But this one lays eggs on ripening fruit, and now it’s getting our attention because that’s what we like to eat.”

The insect punches a hole in the skin of thin-skinned fruits such as strawberries, blackberries and blueberries, and lays its eggs inside, where the larvae develop.

“You can’t tell by looking at the fruit if the larva is in there or not, and you’re eating that larva.”

Drosophila were first observed in California in 2008, and by 2011 they were found in Alabama.

“They came in when we imported fruit from some other country, but we don’t know which country,” East said. “In Alabama, they were first found in Coosa County, but now they’re found in every county of the state.”

East said traps don’t rid an area of the insects; they only help farmers know what type of insects are present so they can make informed choices about insect control.

“We check every couple of weeks to see what kinds of insects are out there. I report this to one of our entomologists at Auburn, and he emails and posts on the Web that this is what we’re finding,” East said.

Farmers, gardeners and home landscapers can check periodically to see what types of insects they need to defend against.

“That could save a farmer thousands of dollars,” East said.

As the midsummer holiday passes and Alabama weather turns from hot to really hot, East recommends weed control, mulch, irrigation and proper pruning as the most important tools for those who love their plants.

“After those four things, then we can talk fertilizers. But if you’re not going to do the other things, don’t worry about fertilizing,” he said.

Whether it’s a pecan tree, a vegetable garden, a fruit orchard or a home landscape, East recommends a thick layer of mulch to help with weed control and to help hold moisture in the ground.

“You can’t irrigate enough through the months of August and September,” he said.

“A stressed plant will get more insect damage and other damage, whatever you’re growing.”

He recommends pine straw or bark mulches or others that break down quickly in a garden or flower bed where the mulch will later be plowed in, but recommends against using sawdust or wood chips in a garden.

“It takes nitrogen to break down the carbon, so that will draw nitrogen out of the soil and can make plants nitrogen deficient,” he said.

“Grass clippings are good mulch, but they break down quickly. I like to leave grass clippings on the yard, unless you have Zoysia grass. If you’re mowing often, that adds organic matter to your grass which is helpful in a drought. If you’re going to use grass clippings for mulch, pile them up and let them go through a heat. And if you’ve used herbicides in your yard, that can get into your tomatoes and kill them.”

East also recommends against using any kind of manure in a vegetable garden less than 120 days before harvest. Some bacteria can be taken up from manure into the vegetable plants, and could be harmful if the vegetables are eaten raw.

For more information, visit aces.edu or contact East at 256-354-5976.

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