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Pepper powdery mildew study funded

California pepper growers are again using Rally fungicide this season, under a Section 18 registration, to fight powdery mildew, but, with an eye to the future, they have also funded new, greenhouse studies to take a closer look at their most serious disease and chemical controls for it.

The California Pepper Commission, charged with conducting production research for the $200 million industry stretching from San Diego to Stockton, this year allocated $48,500 for those studies. That's the lion's share of the commission's 2004-05 research budget of nearly $75,000.

Powdery mildew is a perennial problem for the industry and was at its worst last year. It can rapidly defoliate plants, exposing fruit to sunburn. It is particularly tough to manage because it occurs with great variability. And it has a fearful ability to adapt and develop resistance to fungicides. Fungicides, at best, can only manage it, and none is an eradicant.

Ken Melban, director of crop protection services for the Dinuba-based commission, said the Section 18 for Rally, for the 2004-05 season only, was authorized by the California Department of Pesticide Regulation (CDPR) on June 16.

“This is the seventh time Rally has been given a Section 18 for peppers, and that's a precedent,” Melban said. “The rules usually allow no more than five renewals, but the extension was allowed while a review of triazole, a compound in Rally, is being done by EPA.”

Temporary loss

The extension, which allows Rally to be applied on peppers twice per season in rotation with strobilurin fungicides, was granted only after intervention by the commission, Melban explained.

Rally lost its Section 18 for peppers for nine months during the 2002-03 season because CDPR ruled that the newly registered strobilurin fungicides Quadris, Flint, and Cabrio were available alternatives for powdery mildew.

The commission, however, questioned the efficacy of the strobilurins, Melban said, because the trials used to collect data were done in conditions of relatively light pressure by the disease.

It fell to the commission, he continued, to demonstrate the suspected lack of efficacy of the strobilurins. “CDPR took the position that if products are registered, they are effective. That's not always the case, and we have met with the manufacturers about that.”

The commission argued for the Section 18 on two accounts, he said. First, to manage resistance by the powdery mildew, the strobilurin labeling requires rotation with fungicides with a different mode of action. Rally, a sterol inhibitor, is the only available product having a different mode of action.

Second, the commission agreed to fund new greenhouse studies now under way by Mike Coffey, plant pathologist at the University of California, Riverside. Coffey is inoculating pepper plants with powdery mildew under controlled situations and evaluating the performance of several fungicides.

Prove inefficiency

Results will be announced in February of 2005. The trials are closely contained for complete inoculation by the disease and because the disease could rapidly spread out of control if grower fields were used.

“We hope to prove, once and for all, the strobilurins are not effective on powdery mildew on peppers,” Melban said. The data, he added, will hopefully hasten registration of efficacious materials with other modes of action.

The industry is also interested in learning more through Coffey's research about the onset of powdery mildew on peppers and developing a method to forecast it.

Meanwhile, Bob Heisey, the commission's research committee chairman, is monitoring a host of pest concerns other than powdery mildew for the industry that in a typical year amounts to about 25,000 acres.

Heisey, sweet pepper and fresh market tomato breeder with United Genetics Seeds Co. at Hollister, has been a commission member for nine years.

Despite its high-value per acre, he said, the California pepper industry's comparatively modest acreage offers little incentive to the ag chemicals industry to develop new products for it.

“That's why the commission has taken a more active role over the past five years in supporting gathering of data for registrations to get chemicals growers need.”

Many of the pest problems, he said, are traditionally cyclical in California, and growers never know what to expect from one year to the next.

High costs of hand weeding remain an issue, despite the industry's evolution to predominant use of transplants and rotation with other crops where herbicides are applied. “If growers can avoid sending in a hoeing crew by spraying something for weeds, it is certainly helpful to them.”

The commission has been working with FMC and regulators toward registration of sulfentrazone, an herbicide that performed well in peppers in Monterey County trials. Although a federal registration is advancing, progress in California has been stalled by CDPR requirements for soil dissipation studies, and additional research will cost $200,000 to $250,000. The commission is working with the manufacturer, FMC, to resolve obstacles to California registration of the product.

Potato psyllids, particularly the sooty mold their sugary waste brings on, emerged as a concern in coastal peppers last year, and Heisey said growers have few insecticides that are both registered and effective. The residue is practically impossible to remove and is an economic problem for processing peppers.

Garden symphylan damage, especially to transplants, appeared last year, and the commission has allotted $5,000 to Bill Chaney, Monterey County farm advisor, for studies on the underground pests this year.

Heisey last year studied tomato spotted wilt virus in peppers and came up with observations after consulting with experts on the virus outside California. He and other plant breeders continue to search for resistant varieties, but for the moment attention is on controlling the thrips vector, which occur throughout the season.

His conversations underscored the need to control thrips when plants are young. Acreage of radicchio, a host of both the virus and thrips, nearby can promote thrips infestations in early peppers and tomatoes.

He suggests avoiding early pepper crops near radicchio fields, spraying harvested radicchio fields with a strong insecticide before they are destroyed, and, if possible, working those fields at night when thrips are less active.

Used of imidacloprid (Admire) will discourage thrips on young transplants, he said, not as a direct control but because the insects do not like the taste of the chemical and move on.

The commission, established in 1989, was authorized in February for another five years after an industry referendum. Voting results were 73 percent of the producers approving and 60 percent of the handlers approving. The commission's production research is funded by assessments of 15 cents per ton on each category.

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