California onion growers vigilant in thrips battle

California onion growers vigilant in thrips battle

Growers got the latest disease and pest information at the California Garlic and Onion Symposium.

Growers of onions in California are expected to have a Section 18 clearance for use of Movento, considered an effective insecticide for control of thrips, very soon.

And another weapon for thrips control could be added to the industry arsenal as early as next year with clearance for Torac.

Those were among news elements that emerged in this year’s California Garlic and Onion Symposium held in Tulare.

The symposium opened with San Joaquin Valley onion and garlic producer Kevin Lehar, a member of the California Garlic and Onion Research Advisory Board, tracing the history of white rot and how that drove much of the industry from the Santa Clara and Salinas valleys and over the hills into the San Joaquin Valley.

White rot was an issue in 2012 as well, “really tough,” Lehar said. He is crop production manager for Woolf Enterprises, Huron, Calif.  And Lehar, an onion grower for 25 years, called last season “the worst onion maggot year” he has experienced.

Other speakers talked of high pressure last year from thrips, the most damaging insect pest of onions in California, which scars leaves, cuts yield and can carry iris yellow spot virus.

At the same time, speakers said, damage from garlic rust was down in 2012, but they warned that growers need to keep their guard up and be sure that existing treatments are working.


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Among the advisory board projects is joint sponsorship with the University of California of bee research on seed onion production to determine why there has been a decline in yields.

And Lehar laid out the protocol for avoiding the spread of white rot by using clean, disease free garlic seeds and onion transplants; sanitizing equipment before entering a field and reporting all fields with white rot infestations.

“We can’t do what was done 30 years ago,” he said. “We have to head this off at the pass.”

Lehar is hoping that problems of infestation can be dealt with through “spot treatment” without over-burdening growers.

Mary Ruth McDonald, with the University of Guelph in Ontario, Canada, talked of research on control of onion maggots and seed corn maggots. She said in-furrow applications of Capture and Force reduced damage. It was unclear if Movento had an effect. She said new registered seed treatments work well.

McDonald said Spinosad bait is formulated to attract flies. She said perhaps it could be used at the edge of fields to draw flies away from the main crop.

Seed treatments

Rob Wilson, with the University of California in Tulelake, Siskiyou County, also talked of seed treatments and in-furrow treatments. He said products with Sepresto and spinosad provided superior protection against maggot damage compared to Lorsban.

Among herbicides that Wilson found effective were Goal Tender to control weed seedlings and slow growth of larger weeds at early stages in crop development, and Decathal at planting;

For thrips control, Eric Natwick, UC farm adviser in Imperial County had this advice: Don’t plant onions near small grain crops, overhead irrigation may help suppress thrips populations, control thrips before the early bulb stage, randomly sample entire onion plants by pulling leaves apart and sample at least five plants from four separate areas of a field.

Natwick said it is important to rotate pesticides with different modes of action to avoid target pests developing resistance. He said results of studies on Torac use on larvae appear to be similar to effects of Radiant.

Some insecticides may knock down populations of thrips but also take out beneficials that can lead to increased populations later, said Steve Orloff UC county director with Siskiyou County. He found Movento with Lannate to be the most effective treatments.

Orloff said researchers remain puzzled about why there is considerable year-to-year variation in the pressure from thrips.

Richard Smith, a UC farm adviser for Monterey County, said a material called Zeus shows promise for controlling nutsedge when used as a pre-emergent. He said post-emergent applications are phytotoxic to onions.

Andre Biscaro, a UC farm adviser in Los Angeles County, described a software program called CropManage that can be used to give nitrogen and watering recommendations.

He noted that onions require frequent irrigation because they have shallow root systems and high sensitivity to mild water stress. Researchers plan to monitor three onion fields this year using CropManage, which draws on data on Soil Water Tension and from the California Irrigation Management Information System (CIMIS).

Garlic rust, which caused severe damage in the 1990s in California, is still out there – perhaps in a new form. That’s the word from Steven Koike, UC farm adviser in Monterey County.

Koike said crops need to be monitored closely for disease occurrence, along with weather conditions. He said it’s possible that today’s garlic rust – which can affect onions as well as garlic – is a different strain. Earlier studies showed it did not affect leeks, but today it does. Koike is studying whether materials used to control it remain effective.

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