Some lettuce plants are fighters, fully prepared to deliver a knockout punch to challenges such as bacterial leaf spot.
Others are more susceptible to those blows.
Sorting out which varieties fall into either of those categories was among the research findings presented to the California Leafy Greens Research Board in Coalinga.
The annual research conference was close to a seven-hour non-stop stream of findings from more than 15 researchers whose reports were richly technical, but also contained some practical advice for growers.
Here’s some of what they had to say:
• Carolee Bull, research plant pathologist with the U.S. Department of Agriculture, Agricultural Research Service in Salinas, looked at variability in resistance to bacterial leaf spot among different cultivars.
She found that the variety Little Gem was most resistant and Vista Verde highly susceptible. Another resistant variety is La Brillante, and other susceptible varieties include Salinas and Salinas 88.
Those plants that are able to resist, she said, have a mechanism she termed “hypersensitive reaction” that “turns off” the disease and causes rapid death of some cells, forestalling damage to more of the plant.
Bull likened it to “chopping off your hand because it is diseased so it doesn’t affect your entire body.”
Bull also looked at strains of the disease that differed in virulence.
• Eric Natwick, University of California farm advisor in Imperial County, talked of damage caused by thrips that can affect marketability of lettuce.
He said it is most likely to occur when market value is lowest “when we can least afford it.”
Thrips can also spread diseases like spotted wilt virus.
Natwick explained it is the larvae that cause most of the damage, though adults can disperse the damage. He said there are several effective pesticides to address thrips, including Lannate, Entrust, Radiant, Mustang and Warrior.
Of those, he said, Radiant is most effective, and there is hope of getting a California label for Torac, which he said is also “quite good.”
But Natwick cautioned that Radiant is best used in rotation with other classes of chemicals. “If you keep using the same material over and over, it is not going to work,” he said, urging growers to practice “insecticide resistance management.”
• Tom Turini, UC vegetable crops advisor in Fresno County, said research showed variable responses by lettuce varieties to fusarium wilt and tomato spotted wilt virus.
He said most romaine plaints had lower incidence of fusarium wilt, but there were also a few iceberg varieties with relatively low levels of the disease.
He said Sawa Up had no fusarium wilt in the absence of tomato spotted wilt virus.