New tools show promise for managing strawberry pest
By Bob Johnson Central Coast strawberry growers may soon have enough tools to manage lygus bugs after struggling with the pest for more than half a century. Development of new insecticide alter- natives should provide more help rotat- ing out of malathion, use of which led to widespread resistance because too many growers relied on it frequently to control lygus populations. “By 2010, there were more controls available, including pyrethroids and ne- onicotinoids, so chemicals could be ro- tated,” said Kirsten Pearsons, a University of California Cooperative Extension in- tegrated pest management entomology advisor in Santa Cruz, Monterey and San Benito counties. Pearsons made her remarks as re- searchers discussed lygus bug manage- ment during the 2023 UCCE Annual Strawberry Production Meeting in Watsonville earlier this year. Lygus bugs are the most important in- sect pest in strawberries and are particu- larly difficult to manage in berries grow- ing during the warmer summer months, when pest populations reach their peak. The bugs puncture individual straw- berry seeds, causing fruit to stop growing
near the seeds. This leads to misshapen strawberries that are unmarketable. Recent research indicates lygus may also reduce the size of the berries that are of proper shape. “You start to see a difference in fruit size,” said Mark Bolda, a UCCE farm ad- visor based in Watsonville. Bolda noticed the larger size of berries protected from lygus bugs during his trials of a promising new experimental material, ISM 555. Berries grown in plots treated with the material weighed an average 22.5 grams, whereas nearby berries treated with the pyrethroid Mustang Max weighed an av- erage 16.2 grams, which is larger than the 15.8 grams in untreated plots. “Sometimes the fruit twists, and some- times it doesn’t but ends up being smaller,” Bolda said. The unregistered material did a better job than the pyrethroid in keeping lygus populations down, reducing the number of distorted fruit and increasing yields. ISM 555 has shown residual effect of up to six weeks after application in Bolda’s two years of trials to help get the material registered. It may even be pos- sible to keep strawberries in the ground for two years.
In research trials, a new experimental material, ISM 555, has shown to do a better job than pyrethroid at controlling lygus bug populations in strawberries and reducing distorted fruit.
“The production cost of second-year berries is pretty good, but the problem is you have so much lygus in there,” Bolda said. “If you could control lygus, that second-year strawberry model becomes pretty compelling.” In Bolda’s trial this year, untreated plots produced 1,685 eight-pound boxes. Plots treated with Mustang Maxx yielded 1,874 boxes. But plots treated with ISM 555 pro- duced 2,679 boxes. During the peak period of malathion re- sistance, second-year fields were consid- ered refuges for large populations of lygus bugs with resistance to the most widely
used insecticide. Growers did not want to contend with these super bugs migrating in from nearby second-year fields. For a time early this century, malathion was used so much that resistance became widespread, and control was unreliable. That inspired the search that has led to alternative management tools, both chemical and cultural. As the range of available materials be- comes broader, other lygus management tools have also reduced the need to rely exclusively on insecticides.
See LYGUS, Page 27
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April 12, 2023 Ag Alert 21
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