Just about anything anyone would want to know about lygus bugs was elucidated at the recent Lygus Summit, but Washington State University entomologist Doug Walsh topped everyone with his fish story.
More specifically, how salmon restoration efforts in the Pacific Northwest will likely adversely accelerate lygus bug damage in PNW crops.
As part of the fish restoration effort, stream minders in Washington, Idaho and Oregon are mandating a 100-foot vegetation buffer zone along all salmon habitat waterways. This is to protect against runoff pollution and sedimentation of waterways.
This buffer zone and its associated collection of weeds will also create an ideal habitat for lygus bugs to overwinter and migrate from into adjacent crops.
Walsh said these buffer zones can not be treated with pesticides, except with backpack sprayers for noxious weeds. There will be thousands of miles of stream banks with buffer zones.
Walsh said lygus already infest a wide array of crops, and control is becoming more difficult with increasing pest resistance. This salmon restoration project will only compound the problem for producers.
University of California Extension entomologist Larry Godfrey said San Joaquin Valley cotton producers lose 50,000 bales of cotton annually to lygus bugs.
Cotton losses Even though lygus populations have been low the past few years, lygus losses have continued. "We may be looking at an annual problem" vs. a sporadic problem, Godfrey said.
Traditionally, entomologists have looked primarily to the foothills ringing the valley as a source of overwintering lygus migrations into crops. However, Godfrey said populations are coming more from the valley floor, specifically from weedy fields and orchard and vineyard ground covers.
Seed crops Alfalfa, carrots, onions and lettuce are crops that host lygus, but the plant bug does not damage the crop, according to University of California entomologist Charles Summers.
However, those same crops grown for seed can be severely damaged by lygus bugs.
Three lygus species have been identified in Arizona, according to University of Arizona Extension Entomologist Peter Ellsworth.
While seed alfalfa and other crops host lygus bugs, Ellsworth said the desert in some years can act as a host for overwintering lygus.
"There are three generations of lygus in cotton, although most pest control advisors do not see that," he said.
Seed alfalfa and fallowed summer alfalfa are the biggest sources of lygus migration to cotton and other crops.
Seed alfalfa Economic thresholds for lygus control in seed alfalfa are: early season - four to six lygus per sweep; during bloom and seed set - 8 to 10 lygus per sweep and during seed maturation, 10 to 15 lygus per sweep, according to UC Cooperative Extension farm advisor Shannon Mueller.
However, she adds, "Most PCAs and growers think these thresholds are too high."
To effective control lygus in seed alfalfa, Mueller said growers use Monitor and Supracide to clean up lygus prior to or after honeybees are placed in the field.
During bloom and seed set, Capture plus Thiodan "probably" provide the most effective control of lygus. Another pyrethroids, Warrior, was recently registered and provides good control, she said.
"Temik has been used with variable success early season. Dibrom offers a quick knockdown with little residual control," she said. "Metasystox-R controls immature lygus, but timing is critical. Lorsban has moderate selectivity and moderate residual activity. Lannate and Furadan are used in the Pacific Northwest for lygus control."
Cell phone `sweep net' Lygus bugs pose a threat to the more than 60 vegetable crops growing in the Salinas Valley of Monterey County, Calif., according to farm advisor Bill Chaney.
And, like everywhere else, they are migratory, coming from foothills to field and going from field to field. The can cause blanking both in the field and greenhouse.
Growers and pest control advisors are quick to pull the trigger for lygus because of the high value of vegetables. Typically, 10 to 20 percent of the valley's crops are treated annually for lygus. Some years, he added, it is 100 percent.
"As for monitoring, the cell phone is what PCAs use. When they hear the lygus are coming, they treat," said Chaney. What about sweeping and establishing threshold levels?
"I would say only a handful of the 200 PCAs in the valley even own sweep nets," he explained.
Lygus bug is the "spoiler" in trying to set up a soft chemistry IPM program in the Salinas valley. The more pressing concern is resistance stemming from treating for lygus on three- to four-day intervals.
Strawberries With a threshold of one lygus per 20 plants using a beating tray, IPM also has it limits in strawberries, according to Frank Zalom, UC director of the state IPM project.
"The threshold levels are incredibly low, but they have been verified," said Zalom. Failure to monitor closely can be disastrous.
For control of lygus in strawberries, Zalom said bifenthrin and fenpropathrin are most effective. Methomyl is also effective in most areas while malathion is effective in only some areas. However, resistance to malathion is widespread, Zalom said. Nales is "somewhat effective in some areas."
Pesticide bioassays are revealing that pyrethroid resistance in lygus is "quite high," according to Beth Grafton-Cardwell, UC entomologist based at the Kearney Agricultural Center in Parlier, Calif.
This suggests, she said, that pyrethroids usefulness "may be approaching an end."
While there is resistance to organophosphates and carbamates, this resistance level fluctuates from year to year, she noted.
"There is greater potential for maintaining susceptibility to these pesticides if their use is limited," she said.
"There is a great need for new insecticides for lygus control to provide different chemistries to rotate with and manage insecticide resistance."