Pest Pressures Light
The good news for most vegetable growers is that pest pressures have been unseasonably light. Pests that might normally be raging as the season moved into July were still quiet. All that could change quickly, though, as heat units started to accumulate the last week of June.
“In the Salinas Valley, as far as insects go, it’s really quiet right now. We’ve had a little aphid pressure, but overall there’s not much happening,” said Bill Cheney, UCCE Entomology Farm Advisor for Monterey County.
Miyao said typical springtime diseases, such as bacterial speck and bacterial canker, have not been much of an issue this year on processing tomatoes in the northern regions. Slight russet mite activity has been reported, and Miyao advised PCAs to be mindful of the pest as it may come earlier than normal.
Henry Carrasco, agronomist and PCA with Western Farm Service’s Salinas branch, said downy mildew is causing the most problem for coastal lettuce growers. Carrasco said he is having good luck treating downy mildew with a tank-mix combination of Ridomil and a contact fungicide such as Manex.
“Ridomil is an old compound that’s revived itself,” Carrasco said. “I hadn’t used Ridomil in literally six or seven years and it’s holding its own this year on both romaine and head lettuce in combination with contact fungicides.”
Worm and aphid pressures, meanwhile have been “virtually non-existent” on lettuce and cole crops, he said. PCAs have been treating for leafminer in lettuce.
“We have to be cognizant of leafminer damage because, depending on the size of the crop, even moderate leafminer pressure can set lettuce or romaine back a week of harvest if left untreated,” Carrasco said.
He also expects green peach aphid to start showing up in lettuce and perhaps cole crops, noting that cole crop growers in his area in recent years have been treating more frequently for green peach aphid.
Carrasco noted that the acceptance threshold for even cosmetic insect damage has gotten very high, particularly with value-added lettuce, spinach and other vegetables.
“As the industry has moved to more bagged product, tolerance for insect damage is much lower than it used to be so we’re having to evaluate whether we need an extra treatment for those value-added crops,” he said.
Newer products with short pre-harvest intervals of zero to two days have helped growers keep pests in check right up to harvest.
“Manufacturers have been providing us with fungicides and insecticides to meet the demand of short day-before-harvest intervals that allow us to treat right up to harvest,” he said.