Maybe you’ve noticed this:
The beautiful evergreen tree in your yard is turning brown. You look closer and see small, cone-shaped bags hanging from the branches.
What are they?
And they can kill your tree.
“Juniper, arborvitae, pine and spruce may be killed if completely defoliated and less severe attacks can slow growth,” states data from the Institute of Agriculture and Natural Resources.
Found in eastern Nebraska, bagworms are most common on evergreen trees and shrubs.
Occasionally, you can also see bagworms on deciduous (broadleaf) trees like maple or honey locust trees, said Kathleen Cue, the Nebraska Extension Horticulture Educator for Dodge County.
The bagworm gets its name because it’s a caterpillar encased in a tear-drop shaped cocoon, which it makes from bits of leaves or other plant debris on which it has been feeding.
They tuck the debris into the cocoon so it serves as a camouflage. The bags can be up to 2 inches long.
“The cocoon serves as their protection against weather, but it’s also their house that they move around with them and it’s the thing that keeps insecticides off of them if they’re feeding on something,” Cue said.
An insecticide can be sprayed on the tree, coating the foliage, so when the bagworm eats it then it will ingest the insecticide and the toxin will kill it.
At this time of the year, the caterpillars can be up to an inch long.
“The larger the caterpillars, the more feeding damage they do,” Cue said.
And the more insecticide it takes for them to ingest before it kills them.
On top of that, the insect is getting ready to close up its bag permanently and pupate — change into a moth.
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That means they’re not actively feeding.
So is it too late to spray?
It depends, Cue said.
Most people calling Cue now are given an assignment: Go out and stand very quietly and watch for a while to see if the insect is sticking its head out and chewing on something or if it seems to be perfectly still.
Cue said about half of the people she’s talking to now say the bags are closed and the feeding is done.
The other half of the people say they’re seeing the insects chewing on things.
If the insects are actively feeding, then an insecticide can be applied.
While a milder insecticide could have been used earlier in the season to kill a tiny caterpillar, a more heavy-hitting one that contains the active ingredient Cyfluthrin is needed when the caterpillars are bigger.
Wait until the product has fully dried — usually about an hour — before letting pets or people back into that area.
If the insects aren’t feeding, you can save money by not applying an insecticide now.
Instead, remove the bags. You may need a scissors. Throw the bags in a bucket of soapy water and the insects will drown.
The more defoliation that’s occurred the less likely it is that the tree will recover, especially if there’s been bagworm infestation for two or three years.
“That makes it harder for the tree to survive,” she said.
Looking into next year, Cue advises against applying insecticides in April or May, which is too early, and the products can be washed away by rainfall or just degrade.
“If bagworms are their ongoing issue, they want to hold off application of the insecticide until mid-June,” she said.
For information about other insects and plants, contact Cue at the extension office at: 1206 W. 23rd St., Fremont, NE 68025-2504; (402) 727-2775; or firstname.lastname@example.org.