Concerns about small, numerous bagworms on evergreen trees and shrubs continues to be my top question. Bagworm populations are high this year and control may be needed on conifers.
If you think you don’t have bagworms because you can’t see large webs in your tree, you are incorrect. Evergreen bagworms do not create webs; and trees may need to be inspected closely to see bagworms.
Fall webworm is the caterpillar that creates large webbed nests in shade trees. These large webs are noticeable from a distance and filled with caterpillars and frass. Fall webworms are not much of a concern on healthy, established trees.
Bagworms on evergreens are a concern. These small insects can severely damage or kill an evergreen if populations are high.
Bagworms, the caterpillar of a moth, now range in size from one to one a half inches long. After hatching from eggs in late May and early June, each caterpillar wove a bag around itself and camouflaged the outside with needles.
They have been feeding from inside these protective bags since June. When small, they chew small holes in needles, making them less noticeable. Now that they are larger, they eat entire needles and can defoliate an evergreen.
Because evergreens do not have the ability to regenerate growth from beyond where there are green needles on the branch, this damage can kill branches or entire trees.
Control of bagworms on evergreens is recommended. If they are found on shade trees, control is not needed.
Ideally, bagworms should have been controlled in June when they were small. At that time, they were easier to kill, lower risk insecticides could have been used, and the insect would have been controlled before they did much damage.
It is not too late to control bagworms now. They will continue to feed until late August and if not controlled, severe damage or plant death can occur between now and September.
While low populations of bagworms can be picked off and thrown away (do not throw them on the ground or they will climb back onto the tree); a thorough application of an insecticide such as acephate, bifenthrin or permethrin will provide the most effective control at this time of year.
The sooner bagworms are controlled on evergreens, the better. If you wait too long, severe damage is risked; and once bagworms stop feeding and pupate, insecticides are no longer effective. Pupation occurs in late August or early September.
Bagworms pupate inside of the bag. After pupation (cocoon stage), male moths leave their bags to mate with females who do not leave their bag. Eggs are laid inside the bag with each female producing 500 to 1000 eggs. A good reason to remove and destroy bags seen on evergreens during fall, winter and spring.
During late May and early June of next year, a new generation will hatch. After hatching, many of the caterpillars release a streamer of silk and are blown to nearby trees.
Inspect evergreen trees now for bagworms. If small numbers are found, hand-pick and destroy them. If fairly large numbers are found, insecticide applications applied as soon as possible are justified.
Kelly Feehan is a community environment educator for Nebraska Extension-Platte County.