The experts can't say what the lygus pressure will be this spring in California's San Joaquin Valley, but they do urge early and thorough sampling to set up a baseline for populations to monitor the insect afterward.
Charles Summers, University of California entomologist at Parlier, says, “Vigilance will again be key in dealing with lygus. As of the end of March the impression is that we might see populations a bit lower than in the past. While it appears there are fewer adults, there are a large number of immatures.”
The cold and wet February suggested fewer lygus, although a warm and dry April could speed up development, he adds. With drying of vegetation on the foothills of the west side of the SJV, the insects migrate into crop hosts on the valley floor. On the east side, they concentrate in lush growth along rivers.
Lygus hesperus Knight, a.k.a. the western tarnished plant bug, is a major pest of cotton, fruit and vegetable crops, and seed crops. Alfalfa is both a major overwintering site and a point for early spring buildups of populations.
L. hesperus in the SJV has developed resistance to pyrethroids, once considered “a silver bullet” for lygus control, and some suggest those materials may be approaching the end of their usefulness. Resistance to organophosphates and carbamates also occurs but fluctuates year to year.
Several years after their introduction in the late 1970s, pyrethroids accounted for about 25 percent of all insecticides used in agriculture and public health and half the world's cotton insecticides market.
There is interest in new materials to be used in rotation to manage resistance. Entomologists also call for materials that also have greater selectivity for lygus and reduced loss of beneficial species.
Another proposed control step is giving more attention to insecticide resistance management (IRM), including setting aside untreated refuges to preserve susceptible gene-pools and prevent total resistance.
Sweeps are taken with nets at five to 10 locations in a field, and, in addition to counts of adults and nymphs, developmental stages are observed for timing of insecticide applications for the greatest effect.
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