For Release June 11, 2006
Bagworms Are Now Active
by Chuck Otte, Geary County Extension Agent
Bagworms are an annual insect pest. If we treat them in a timely fashion, they will do little damage and they will be easily controlled. If we wait until late August when we can see the damage driving down the street at 30 m.p.h., then control is going to be nearly impossible and your plants may suffer severe damage.
Before we go any further, let’s clarify what we are talking about. Bagworms are the little insects that feed, primarily, on junipers/cedars. They take bits of the foliage of the host plant and attach it to the little silken bag that they stay inside for most of their juvenile life stage. Bagworms are not the caterpillars that make the large, messy webby “bags” on the ends of deciduous tree branches in late August and September.
The adult bagworm is a moth, but one you’ll rarely see. The female is wingless. When the bagworm adults emerged late last summer, the female attracted the male with pheremones. After mating she crawled back into her little bag, filled it with eggs, and then died. That one little bag may hold anywhere from 400 to 1,000 eggs. Those eggs start hatching in late May and hatch over a four to five week period. We are about half way through that egg hatching period so it is time to start treating for bagworms.
When all those bagworm eggs hatch, the little bagworm caterpillars immediately find a spot on the host plant and start feeding. They very quickly make a little silken bag which they will decorate with bits of foliage. These bags are going to be very small at first. They will be easy to overlook as they may only be one quarter inch long. Early detection of bagworm infestations can be difficult. If you are looking for the bags, you have to look close to see them. The first clue is often not the bags at all, but a change in the color of the host plant. Before entire parts of the plant are eaten bare, the plant starts to develop a pale, off green or yellowish green look. If you see this, start looking closer for the tiny little bagworm bags.
As they grow, their appetite grows and they keep making their little bag bigger. By late July or early August these bags will easily exceed an inch in length and they start to become very visible, as does the damage as they strip entire branches of all foliage. By this time, their feeding cycle is almost through and treatment is literally too late.
Even though bagworms will feed on over 200 species of plants, our biggest concern is with their preferred food source, plants in the juniper family. Just because you have junipers or cedars, doesn’t mean you should spray them. If you have had bagworms either of the past two years, I would spray. If you have an immediate neighbor that had bagworms last year, I would spray.
There are literally hundreds of products labeled for bagworm control and they’ll all work well. The trick is not what product you use, but how you spray. You need to thoroughly cover all foliage with a drenching spray. A one or two gallon pump up cannister sprayer is not going to do it. You need a sprayer that you put on the end of your hose and then treat the plants to the point of runoff. Treat once now, and then apply two more treatments at ten day intervals. There are biological controls that are also very effective, IF you apply them early, while the bagworms are still small.. These are applied just like traditional insecticide products, use a hose end sprayer for these products also.
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