Lettuce growers wary of plant virus after Dec. rains WhilemostCalifornianswholeheartedly embracedDecember’s wet start towinter, one group welcomed the rainmore wari- ly—lettuce growers in the Salinas Valley. “It’s a blessing, yes, we need thewater,” said Tony Alameda, managing partner of Topflavor Farms in Monterey and San Benito counties. “But, oh gosh: with that water, here come the weeds, here comes the habitat, here comes all the other problems that go along with it.” weekafterweek, until you’re just like, ‘Ugh, there’s nothing here to even harvest.’” After “100% crop failure” that year in his prime fields at the heart of the Salinas Valley, Alameda tried to dodge the virus in 2021, shifting lettuce plantings to San BenitoCounty and insteadusinghismost valuable land for unaffectedcrops suchas cilantro, leeksandradishes.Bydecamping to San Benito, Alameda was able to har- vest 70%of his usual lettuce yield. Richard Smith, a University of California Cooperative Extension vegetable crops and weed science farm advisor for the Central Coast region. Recent studies have identified several weeds as key “reservoirs” of thrips, in- cluding malva, marestail, and hairy flea- bane. The ubiquitous mustards, fortu- nately, appear to be poor hosts for thrips, although their pollen serve as potential food sources. pesticide application or a beneficial in- sect that could deter the thrips. However, both Alameda and Zischke pointed to the breeding of more resistant lettuce varieties as the ultimate solution to INSV—albeit one that is years away. “We have a lot of different types of let- tuce that we grow, so to move resistance into all the different types of lettuce we grow throughout the season … that’s go- ing to take time,” Zischke explained.
Weeds are overwintering havens for a tiny insect called the Western flower thrips, which in turncarries the impatiens necrotic spot virus, or INSV, a plant virus that caused $100million in lost gross rev- enue for Salinas Valley growers in 2020. The agricultural community called it “thebiggest problemwe’ve seen ina long, long time,” said Mary Zischke, facilitator of a task force convened by the Grower- Shipper Association to address INSV and a related affliction, Pythiumwilt. Since INSV was first observed in the state in 2006, the virus—which poses no threat to people—triggered significant crop losses in 2019, leading up to a cat- astrophic 2020. As Alameda’s lettuces began to show the telltale “bronzing” of the leaves, efforts to bag up or remove the infected plants hadno effect on the virus’ implacable spread. “Nothing seemed towork,” he recalled, “and you just watch those fields collapse,
Generally, growers enjoyed a reprieve fromvirus pressures in 2021. Even in this “good” year, however, about one-third of all lettuce plantings in the Salinas Valley had at least a low level of infection. “Since we were attributing a lot of our so-called good fortune on having less damage this year to the cooler weather, we know we can’t count on that to get us out of this problem,” Zischke said. “All the models point to the fact that we’re in a warming climate, so we were fortunate this year.” Heat waves were a major driver of the INSVdisaster of 2020. Although research- ershaveestablisheda linkbetweenwarm- er temperatures andpopulation increases of thrips, science still has a lot to learn. “Thrips are something we’re try- ing to understand as much as we can, but it’s pretty tough because they’re a little mysterious in the way they get around andwhere they overwinter,” said
Controlling thoseweeds is a toppriority during the winter months, according to Smith. Aggressive weed management in the preceding winter was an important factor in limiting the virus’ spread in2021. Because weeds recognize no bound- aries, experts are also urging managers of nonagricultural lands to keep their properties as clean as possible, includ- ing industrial sites, equipment yards and the edges of roadways—namely U.S. Highway 101, which runs through the center of the valley. Some growers have been volunteering to weed their neigh- bors’ vineyards. “We’re encouraging everybody, as best they can, to knock down known weed hosts; that’s really critical,” Zischke said. Within the grower community, there is “nervous optimism” for the coming year, saidAlameda, as he continues tohope for an innovation that would aid in the fight against INSV—whether a more targeted
Research funding from the state and USDA—as well as projects supported by the California Leafy Greens Research Program—can help expedite that pro- cess. But, for Alameda, the INSV crisis underscores the need for more resourc- es and farm advisors such as Smith, who has spent more than three decades cul- tivating relationships and building trust within Salinas Valley communities. Alamedawould like toseea renewed fo- cusonbringing “bright, young, passionate people who live and breathe this stuff” to the region, sogrowers arebetter equipped to handle the inevitable next calamity. “Hopefully this is awake-up call to all,” he said. “This is a valued industry—you have to take care of it; it cannot be taken for granted. The ‘salad bowl of the world’ cannot rest on its laurels.” (This article was originally published by University of California Agriculture and Natural Resources.)
8 Ag Alert February 2, 2022
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