New worm control chemistry shows some promising results

Over the last two years, a half dozen products from a new chemical group have become available for worm control in a wide range of vegetable and field crops.

The new chemistry, called diamides, is unique in that it provides systemic control of worm nymphs and can be applied to the ground even before the crop is planted.

"There's an opportunity for a systemic product that affects worms. It is the first systemic worm control material," said David Haviland, University of California Cooperative Extension entomology farm advisor.

Although the diamides only work against the larval stage of worms, some of the new products are mixes that also control worm adults or help to control other pests like aphids or leaf miners.

"These diamides can definitely be a good part of a rotation. If you do have crops with worm problems the first four weeks, a pre-plant diamide is an option," Haviland said. The diamides are all in Insecticide Resistance Action Committee group number 28, which is the latest classification.

The one concern with these products is their toxicity to aquatic life, which makes control of leaching or runoff essential, Haviland said. The labels for some of the diamide products require vegetative buffer strips for applications close to streams and creeks. The chemical class has low mammalian toxicity, is relatively soft on beneficial insects and is easy on bees.

There are already a half dozen new products in this new chemical class, which works by depleting the pests' calcium, which in turn reduces the muscle function to the point that the pest suffers paralysis and death.

"It's a larvicide that takes ingestion. You get a flaccid, crunched up look to the worms," Haviland said.

Some of the diamide products also give some leafminer suppression, but not as much as the worm control. Some of the other products give a measure of aphid control. And most of the combination products add adult worm control to the nymph control from the diamide.

Another new chemical in this class, which is not yet registered, will add whitefly suppression to the mix.

"This new diamide has whitefly activity as well as better leafminer control," Haviland said. This newest diamide chemical is not yet registered.

In a UC trial on cabbage loopers and beet armyworms in celery in Riverside County, the new chemistry gave control comparable to the carbamate material lannate.

University of Arizona Cooperative Extension entomology advisor John Palumbo reported good results in multiple trials of the new chemistry in Yuma on worms in both lettuce and broccoli.

There is hope the new class of materials can be used to reduce the number of insecticide applications needed in desert areas, where worm pest pressure is frequently intense.

"The standard in the desert is five foliar sprays for a lettuce crop. They're trying to see what they can do with a pre-plant application of the diamide Coragen to the soil. The pre-plant diamide plus two foliar sprays were comparable to five foliar sprays in multiple trials," Haviland said.

Results from trials in the Yuma area show that a pre-plant application of a diamide to the soil is worth it when the weather is still hot enough to make for strong worm pressure.

"The net effect of all of this is for a September planting they were able to save one or two sprays," Haviland said.

(Bob Johnson is a reporter in Magalia. He may be contacted at bjohn11135@aol.com.)