The time to begin scouting for bagworms has arrived. Memorial Day has always been regarded as the time to begin looking for the bagworms in Kansas. Their hatch typically begins in mid to late May and continues through mid to late June. So, tiny larvae already are chowing down on deciduous plants, as well as evergreens.
Their timing sets the schedule for three possible control strategies — one of which should occur soon, according to Jennifer Smith, horticulturist with Kansas State University Research and Extension. Smith suspects that if an insect census were possible, it would find bagworms are on the up side of a population cycle. Her observations suggest infestations have been increasing for several years.
“We’re more likely to notice bagworm damage on the evergreens. In fact, a string of years with heavy, uncontrolled infestations can actually kill a big, tough windbreak tree,” Smith said. “Evergreens simply can’t replace lost leaves within a matter of weeks, as deciduous trees and shrubs can.”
But, even when lack of food or natural predators (e.g., ichneumon wasps) are keeping bagworm numbers in check, each female still can lay up to 1,000 eggs.
“We’ve undoubtedly got lots of tiny larvae making their way into the world now, often dropping from their mother’s old pupal bag on a fine silken thread,” Smith said. Some of the baby bagworms will stay where they are to feed. Others will literally sail — float — to other plants when wind catches the thread they’ve spun. Prevailing winds’ role in spreading bagworms is why infestations often are heavier on the south and west sides of landscape plantings, Smith said.
At first, bagworm larvae are about one twenty-fifth of an inch long, but they quickly start eating, growing and spinning their own tiny bag. Within weeks, careful examination can reveal them slowly, slowly moving.
“When you can see a plant is infested — or you know it’s likely to be infested again this year — then you decide on your strategy,” Smith said. “If you want to spray, for example, you could buy an organic or conventional insecticide that’s labeled to control bagworms and safe to use on the plant in question. Or, if the application is likely to require stilts or a ladder, you might contact a professional about doing the job.”
When an infestation is new or last year’s damage was slight, a single spray can do the job, applied after mid-June (i.e., the end of the hatch) but before the second week of July (i.e., before the larvae grow to be more damaging). For repeat infestations where even tiny larvae’s feeding could cause an additional plant setback, two sprays are the better course — one applied ASAP and the other, two to three weeks later.
“Or, if you’re striving to adopt ‘green’ approaches and are willing to accept this year’s damage, you can wait until this year’s crop finishes their bags. You can pick off and dispose of them then,” Smith said.
Kansas Bagworms Have Range of Food Favorites
In Kansas, bagworms are widely recognized as a notable pest of eastern red cedars and junipers. Among the evergreens, however, they’re also likely to attack any arborvitae, spruce or pine.
The array of deciduous trees, shrubs and ornamentals that can serve as bagworm hosts include the barberry, blackberry, box elder, cherry, clematis, crabapple, elm, locust, maple, oak, peach, pear, poplar, pyracantha, quince, rose, sumac, sweetgum, sycamore and willow.
If they end up defoliating a host, the bag-spinning larvae can migrate in search of another. If they cannot find a preferred plant, bagworms also can feed freely on clover, ragweed, parsley and nightshade.
Pratt, Kan. —
