Bagworms are eating on more kinds of plants this year

Bagworms are always bad, growing their unsightly brown bags and munching on evergreens.

But they’re really bad this year, moving on to plants they usually don’t bother — like roses.

Now is the time to go after them if you see them on trees or shrubs — before the new bags get too reinforced to penetrate and the damage is already done.

“I expect them to be a little bit worse because the environmental conditions favored their growth,” extension agent Matthew McKernan said Friday, referring to the mild winter and the moisture they received this spring.

In addition to higher numbers of them, “we’ve seen reports of bagworms on lots of different plants, not just junipers and evergreens. Those are their preferred food sources, even though they can eat on a wide variety of trees and shrubs.”

When scouting for bagworms, start with evergreens. You can often see the old bags from last year still hanging on. But those now are probably just shells because the eggs that were in them have mostly hatched, turning into little worms about the size of a sharpened pencil lead. They have started spinning their own bags, which will soon be filled with eggs to start and expand the whole process for next year.

The small bags look like the bigger ones, but they usually have parts of the plants attached to them to try to camouflage them, McKernan said.

“We had a rose come in that had holes in the leaves and some skeletization of the leaf where they ate parts of the leaf,” McKernan said. “You could see the bagworm still hanging from the leaf. That’s how we were able to identify it.”

The worms pop up out of the tops of their bags to eat.

“The majority of them have hatched at this point,” McKernan said. “That’s why we recommend the second part of June or after June 15 to start control because we want to make sure we get as many of the bagworms as possible when we spray to best protect our plants.”

If you see only a few bagworms on a tree or shrub, pick them off and destroy them. If there are too many for hand-picking, plan to spray. Be sure to do a thorough job, spraying from top to bottom and from the outside to the interior of the tree, McKernan said.

Insecticides commonly used include spinosad (in Conserve); Fertilome Borer, Bagworm, Leafminer & Tent Caterpillar Spray; Captain Jack’s Dead Bug Brew; Bonide Caterpillar Killer; bacillus thuringiensis (Dipel, Thuricide); acephate (Acephate, Orthene, Bonide Systemic Insect Control); cyfluthrin (Tempo, Bayer Vegetable & Garden Insect Spray), and permethrin (numerous trade names).

Spinosad and bacillus thuringiensis are both organic, but spinosad is more effective, especially on larger larvae.

But it’s best not to wait to let them get bigger, McKernan said. The damage only increases, and they only get harder to kill, meaning that their bags will overwinter to spill more eggs and increase the problem exponentially next year.

This story was originally published June 17, 2016 at 5:15 PM with the headline "Bagworms are eating on more kinds of plants this year."