SANTA MARIA VEGETABLE MEETING

Central Coast Meeting:

Updates Growers/PCAs on Pests and Diseases

By Patrick Cavanaugh, Editor, and Laurie Greene, Associate Editor

Crowd Listens in the Bonipak Conference Room,

At the UC Annual Santa Maria Vegetable Meeting today in the Bonipak Conference Room, about 75 growers, PCAs and others came to hear the latest in vegetable disease and insect management, as well as food safety and proper pesticide use.

Steve Koike, UC Cooperative Extension plant pathology Farm Advisor in Monterey County, spoke about diseases of coastal vegetable crops.

Koike elaborated on new races of downy mildew. “About every 18 months to two years, we see a new race. Currently we are on race 14, and we still have races 10 through 13 affecting crops,” he said, adding, “2013 has been fairly quiet for downy mildew.”

Steve Koike

“With the increased variety of crops, we see an increased variety of root rot diseases such as Pythium, Phytophthora, Fusarium oxysporum, and Rhizoctonia. For instance, with the higher popularity of spinach, we see more root rot issues.” He noted that growers are seeing a buildup of Pythium in their fields, which affects the plant early in the season and causes the whole root to die. While Phytophthora is still quite rare, Fusarium is less rare and causes the root tips to turn back. “Rhizoctonia is the third major disease affecting older plants, again, turning the root tips necrotic black.”

Koike then spoke about several viruses that affect Central Coast crops. He said that impatiens necrotic spot virus (INSV) has been found worldwide; in Salinas, INSV has been discovered on lettuce. “It’s very important in lettuce but it can also be found in basil, celery, endive, fava bean, peppers, radicchio spinach, and tomato plants. We have lettuce fields in Salinas with 60% INSV, and growers walk away from these fields,” he said.

“INSV and many other viruses are vectored by thrips, which are difficult to manage all season long,” noted Koike.

Other major viruses include lettuce necrotic stunt virus (LNSV) and tomato bushy stunt virus (TSWV).

“We are seeing yet another virus, tomato spotted wilt virus, starting to show up on artichokes. Artichokes are a known host, but it is rare to see the virus affect the crop by causing necrotic streaking in the plant’s stems,” said Koike. “We are concerned that it could be a new strain.”

Koike explained that some Wilt diseases found elsewhere are now moving to the Salinas Valley. For instance, Verticillium Wilt and Fusarium Wilt damage on lettuce have not been detected in this area yet, but need to be watched.

“Before the restrictions on methyl bromide, we did not see these wilt diseases when lettuce and strawberries were rotated around each other,” Koike commented.

“As growers phase out methyl bromide, they have been using bed fumigants of straight Chloropicrin or Chloropicrin plus Telone,” Koike continued. “These have not been as effective as methyl bromide, so when fields are reworked for the next rotation crop, more Verticillium is present, causing yield decline.”

Koike then turned to powdery mildew in Salinas, which is becoming more important in Salinas, especially on lettuce, which had normally not been a problem.

“Powdery mildew on celery is increasing in that now we can see significant symptoms,” Koike remarked. “In fact, if growers can see the symptoms when they drive by the field, then you know there is a problem,” he said.

In other topics at the annual meeting, Heather Scheck spoke about bacteria wilt and brown rot in potatoes caused by Ralstonia Solanacearum.

Heather Scheck

“This wilt is very difficult to control, and it could eventually be a problem in North America due to a new race known as Race 3, Biovar 2,” she said. “At risk are both tomatoes and potatoes.”

Scheck said that the ornamental geraniums are a big host plant of Race 3, Biovar 2. “Geraniums are imported to the U.S. from the Netherlands, Kenya and Guatemala, and a big outbreak for Race 3, Biovar in 2004 forced crop destruction in these countries to prevent exportation of the bacterial wilt,” she said.

“There is no chemical treatment for the problem in geraniums,” Scheck said.

Lisa Blecker

Also speaking was Lisa Blecker, Pesticide Safety Education Coordinator with UC Agriculture and Natural Resources (UCANR), UC Davis.

She focused on crop protection product labels and the importance of following the label especially specific use restrictions. Pesticide tolerances are legal residues, based on the EPA allowances.

“Most crops have pesticide residues, but they are far less than what causes harm to consumers. Tolerances are critical for human health,” she noted.

Tolerance is based on:

Good human health, with no observable harm
Assumption of maximum use of product
Assumption of maximum applications per year

“If growers or those who apply products follow label directions, you will not go over tolerance,” she said.

Surendra Dara, Strawberry and Vegetable Crops Advisor/Affiliated IPM Advisor for San Luis Obispo County spoke about managing thrips on lettuce, aphids on broccoli and the new invasive pest, Bagrada bug, on cole crops.

Surendra Dara

“Western Flower Thrip is a sucking insect that vectors viruses,” he said, “and I did experiments on lettuce using many different products.”

Research has found that thrips can be significantly lowered with chemical treatment versus untreated control. “Softer materials such as Tolfenpyrad alone or with methomyl provides good control,” he said. “Also, some microbial products have potential for thrip management.”

Surendra then spoke about the cabbage and green peach aphid, a particular problem for broccoli, especially at post harvest. He tested several control products in a trial.

He noted Asana did very well on cabbage aphid but not as good on green peach aphid. “However, tests showed that Dow AgroScience’s Sulfoxaflor provided good control for both aphids species.”

“We also treated aphids with a friendly fungus called Beuveria Bassiana, that is showing promise,” Dara said.

Dara moved on to the Bagrada Bug, which was discovered in Los Angeles County in 2008 and is now prevalent in all southern California counties, plus Monterey County. “This pest has a wide host range of vegetables and ornamentals,” noted Dara. “And there is a low threshold for damage because one adult per 10 foot row of seedlings or transplants will cause a stand loss.”

Dara said it’s important to identify the adult Bagrada Bug and closely monitor it during the early 5-6 leaf stage of plants.

“There are many different registered control products that are effective for the pest,” Dara said. He is also working on non-chemical controls such as Fungi, NoFly and essential oils, all of which show promise.

According to Dara, cultural control could: