Weeding, weather aid battle in controlling lettuce virus
By Natalie Hanson California lettuce growers are so far breathing a sigh of relief that the dread- ed impatiens necrotic spot virus that has devastated Salinas Valley lettuce crops in recent years seems to have receded. But agricultural researchers warn that it will take extensive work and vigilance to prevent a future outbreak that could be costly for affected crops. For Monterey County farmer Ryan Kelly, that vigilance includes weeding every day early in the morning. Kelly, farm manag- er at Boutonnet Farms in Castroville, said weeding is essential to keep tabs on dis- ease spreading thrips and area plants on which the virus, or INSV, can live. “We try to be as preventative as possible and keep things as clean as possible,” Kelly said. “Occasionally, we get the people that let things go a little longer than you might want, but for the most part, things have been better.” Kelly is among the growers who are working again this season to avoid anoth- er outbreak of INSV, an obligate parasite that finds hosts in plants, including winter weeds, and is vectored through western flower thrips. It can wreak havoc on lettuce crops
during the growing season. Salinas Valley farmers in 2022 suffered an estimated $150 million in crop losses, more than tripling the damages from 2021. Last year, exceptionally wet and cold conditions from atmospheric river storms resulted in a dramatic reduction in INSV infections. This year, farmers, agricultural officials and scientists are working to keep infection levels from rising anew through monitoring and aggressively targeting po- tential weed hosts for the disease. “It is hard to evaluate whether or not the weed abatement program is working, but the industry is optimistic that it has made a difference,” said Jennifer Clarke, execu- tive director of the California Leafy Greens Research Board. “I think that is something that time will help us evaluate.” Growers in the Salinas Valley are getting help through county weed abatement ef- forts and from California Department of Transportation crews that clean up weeds along Highway 101 on the southern end of the valley. “Hopefully, they’re getting to it sooner rather than later, because it’s still pretty plugged up along that stretch of Highway 101, along the northern end of the corri- dor,” Kelly said.
Weed control near farms is a critical part of prevention efforts for impatiens necrotic spot virus. The disease, which can be devastating to lettuce crops, finds hosts in weeds and is spread by thrips.
There is another benefit of preventive weeding: It costs less to do so preemptively than to face the potential high costs of crop damage if any crops are impacted by INSV, Kelly added. “Even if it costs a little bit more money, I think it’s worth more to me in the long run than if I let it go,” he said. Yu-Chen Wang, plant pathologist
advisor at the University of California Cooperative Extension in Monterey County, said things are finally looking up in the state’s INSV hotspot thanks to efforts by Salinas Valley growers. “So far, we have seen a low population of thrips and a low incidence of INSV,”
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