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Cabbage loopers top vegetable watch list

Tomato growers in the Sacramento and San Joaquin Valleys are contending with the usual suspects, and some unusual ones, in their pest and disease line-up, according to a recent newsletter by Gene Miyao, farm advisor for Yolo, Solano, and Sacramento counties.

At the top of the list are cabbage loopers. They don't normally warrant treatment, but this season Miyao urged growers to keep a close watch on fields more than six to eight weeks from harvest.

The foliage-feeding worms are a hazard for more mature fields where the loss of full-leaf cover exposes the crop to sunburn and for younger fields where vigor reduction might occur.

Miyao, who is monitoring trials for looper impact on yields and soluble solids, is recommending Bts as the preferred treatment as needed, since, he says, they are both effective on the pest and easy on beneficials. Particularly notable among the good guys is the Hyposter parasitic wasp that also goes to beet armyworm and other larvae.

Looper flights continue as indicated by trapped moths, and eggs are also present on the leaf below the highest open flowers of a plant. Looper eggs resemble those of tomato fruitworm but have a more flattened shape.

Russet mites

Miyao says russet mite outbreaks are also occurring, and evaluations by University of California entomologist Frank Zalom and others link mite damage closely to early fruit sizing.

The interveinal chlorosis and brown spotting of Fusarium foot rot are more common this year, according to some growers. UC researchers continue to track the disease with support from the California Tomato Research Institute, but no control has been found. One approach has been to limit the spread of contaminated soil from one field to another.

If abnormal weather patterns continue this year, Miyao is fearful unseasonable rains might set off late blight, which responds to a series of rainy days followed by moderate temperatures. However, a day or two of rain followed by drying weather is not a likely hazard.

Bravo, Quadris, and Dithane have been effective as preventive treatments, Miyao said, adding that timing of application was more critical than fungicide selection.

He also recommended watching for blackmold fruit rot and said a single fungicide treatment four to six weeks prior to harvest has usually controlled the disease. But in under higher disease pressure, one application may not be enough.

Meanwhile, to the south the Curly Top Virus Control Program has alerted growers CTV infections reported in tomatoes and sugar beets from Los Banos to Maricopa along the “I-5 corridor.”

CTV attacks many vegetables and other crops and has been responsible for several massive crop losses since 1950, including one in 1990.

Project leader Bob Peterson of the Fresno-based program, says populations of the sugar beet leafhopper, the vector of CTV, increased after a favorable overwintering in the foothills along the west side of the San Joaquin Valley.

Potential grows

Fallow fields with Russian thistle, mustard, pigweed and other hosts on the valley floor also encouraged massive reproduction of the leafhoppers. When foothill and valley floor populations combined, the potential for infection became staggering.

The program treats about 65,000 acres for BLH with malathion each year, but it depends on growers cooperating to control weedy fields and topping sugar beets. This year one problem was when growers failed to disk fallow fields until after new crops were planted. As the disking was done, the BLH dispersed into the new fields.

Peterson says if there's any good part to the news, it's that the strain of the virus is relatively mild this year.

That's scant solace, since he also says numerous other viruses borne by aphids and thrips are just waiting for ideal conditions in the SJV.

e-mail: [email protected]

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