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California cotton threatened by Fusarium Race 4California cotton threatened by Fusarium Race 4

Fusarium Race 4 has been around awhile, but with the expanded cotton acreage this season it has been found in far more areas than ever before. It has been identified in all six SJV cotton-producing counties in more than 200 total locations.

Harry Cline 1

September 1, 2011

8 Min Read
<p> Cannon Michael, chairman of California Cotton Growers Association.</p>

California’s cotton comeback is in a Catch-22 quandary.

As the economic outlook for the long-time San Joaquin Valley crop staple improves, the capability to continue to expand cotton acreage in the future is being threatened by an insidious soil fungus, Fusarium Race 4.

This particular race has been around awhile, but with the expanded cotton acreage this season it has been found in far more areas than ever before. It has been identified in all six SJV cotton-producing counties in more than 200 total locations.

Although not as menacing elsewhere, it also poses a threat to the rest of the U.S Cotton Belt and could have an impact on California as a source of premium cotton planting seed for varieties to be sold throughout the U.S. and the world. However, other areas of the U.S. Cotton Belt could have their own soil-borne Fusarium nightmares just like Australia, where the first Race 4 was found.

Fusarium Race 4 FOV was first identified in California in the 1990s in isolated areas. It is believed to have been introduced into the valley on infected planting seed. Unlike other Fusarium races, Race 4 does not need to be vectored by nematodes to infect plants. It has been found in all soil types. It cannot be eradicated. Once it is in the soil, it does not go away. A widely infected field cannot produce cotton ever again.

It is spread by Race 4 contaminated soil movement, plant debris and seed. It only kills cotton, but it can live and spread in the soils where crops other than cotton are grown without affecting those other crops. When cotton is planted to a field, even after years or more of no cotton, the fiber crop can be devastated.

That is what happened this year when California’s cotton acreage took a sharp jump to 450,000 acres from a historical low point of less than 300,000 acres three years ago.

California cotton industry leaders have initiated an aggressive information and hopefully an expanded research effort to contain the spread of Fusarium Race 4.

Los Banos, Calif., cotton producer and California Cotton Growers Association Chairman Cannon Michael said with the declining cotton acreage since 2004, Race 4 was “something growers ignored and did not realize the extent of the problem until this year. With expanded acreage, it has popped up everywhere. It is no longer localized in just a few fields.”

Fellow growers Bill Stone in Kings County and Mark Watte in Tulare County, along with others, have been “very vocal about this and are adamant about an educational program and continued research program to bring Race 4 more to the forefront,” said Michael. ”Unfortunately, there are still some growers who do not understand what we are up against.

“Industry leaders and seed companies are also very involved in our efforts,” Michael said.

“Race 4 is a deadly early-season disease,” said Michael.

Impact on seed production

Not only is turning back Race 4 critical to lint production in the valley, it could also have a devastating impact on an important element of the valley’s cotton industry — seed production.

Premium certified cotton planting seed is produced in the valley for varieties sold not only within the valley, but elsewhere in the U.S. and world. Michael said it is critical to protect that part of the state’s cotton industry.

The first line-of-defense against the spread of Race 4 is planting resistant varieties and avoiding susceptible ones. Race 4 is particularly lethal to Pima. Fortunately, phytogen 800, the most widely planted Pima in the valley, is highly resistant. Deltapine 744 Pima is highly susceptible, but is not grown any more. Pima 830 is susceptible at high Race 4 inoculum levels. Phytogen 802RF appears to be tolerant. Phytogen 805 Pima was thought to have good tolerance, but it broke down this year under high Race 4 inoculum levels.

Acalas at one time were not thought to be susceptible to Race 4, but that is no longer the case. Bob Hutmacher, University of California Extension cotton specialist, said he has seen high plant stand losses to Race 4 in Phytogen 725, Phytogen 755 and Daytona.

“It is unusual to see a field wipeout, but stand losses of 30, 40 or 50 percent can happen. I have seen half a dozen fields this year with stand losses of greater than 50 percent in Acala by mid-squaring without a susceptible Pima,” said Hutmacher.

The inoculum levels may be initially low in a field, but can spread rapidly with the planting of a highly susceptible variety.

The UC cotton website has a wide range of information about recognition and containment of Fusarium. Go to http://cottoninfo.ucdavis.edu/.

CCGA President Earl Williams said the ultimate solution to the problem is development of more resistant Acala and Pima varieties, but that is at least five to 10 years away in the best scenario. In the meantime, growers must educate themselves on what to do to stem the spread of Race 4.

Williams said research money will be directed at chemical and field treatments. Soil solarization is a possible option, but it is an expensive one and can likely be used on small acreage. Seed treatment and using injected steam to kill the organism are other possible ways to combat Race 4 spread.

Focal point

The focal point of this research is at the USDA Cotton Field Station at Shafter, Calif., and it is on the federal budget chopping block.

“We are doing everything we can to keep Shafter open,” said Williams. “The Shafter station is vital to addressing this problem because the disease is there where researchers can do plant genetic and field work in helping us find solutions.

“Moving the Fusarium Race 4 research to another USDA-ARS lab makes no sense for the California cotton industry,” Williams said. It will take considerable political clout coming from across the Cotton Belt to keep Shafter open, but the industry is pulling out all the stops. The National Cotton Council was at the initial Race 4 workshop meeting earlier this summer to initiate the war against the disease.

“We have distributed information about Race 4 to cotton growers who visit California as part of the Producer Information (PIE) tour each summer to make sure others understand how important the work is that we have going on at Shafter,” Williams added.

Michael admits he did not expect Race 4 to reach the northern area of the San Joaquin Valley where there is limited Pima acreage. However, it has. It is on his farm and in areas around Firebaugh and Dos Palos.

“If you plant a very susceptible variety, the disease will exploit that and spread,” Michel said. “We cannot understate the severity of this problem.”

Michael said Race 4 limits a grower’s rotational choices. Watte, according to Michael, has already red-lined some of his Acala fields for cotton because Race 4 is so prevalent in them.

On his family farm, Bowles Farming, Michael has tested soils for Race 4 and found it. It can only be positively identified through laboratory analysis. He has rogued plants from small, infested areas. “We have irrigated, fumigated and tarped those areas for solarization to try to stop it. We also are looking at using machines that inject steam into the soil to kill the fungi.

“It is a scary situation,” he said.

Opportunistic pathogen

Hutmacher called Race 4 an opportunistic pathogen “that stays in the soil waiting for you to plant a susceptible variety.” Under ideal environmental conditions for it, Race 4 can explode and this was the year for it because of late, wet planting conditions that stressed seedling cotton.

Conversely, wise management decisions to avoid those conditions could put growers in a better position to ward off the menace.

This includes first planting a tolerant variety. “The higher the resistance; the better,” Hutmacher urged.

“Planting dates are critical. Generally, the warmer the conditions where the plant’s root system can grow rapidly, the fewer pathogens will attack it. You don’t want to play into this disease’s hands. We remind growers that this is an early-season disease,” Hutmacher added.

Anything that makes a plant struggle early may weaken it and make it susceptible to Race 4, Hutmacher said.

“One of the problems with Race 4 is that it can survive nicely on a wide collection of plants and weeds without infecting those plants or weeds. The pathogen lives on root surfaces and can persist for years. It will not go away,” Hutmacher said.

The cotton Extension specialist praised PCAs and many growers for being alert to the problem this year and identifying suspect areas to be tested.

Heretofore, Race 4 has been a California problem, although suspect races have been found in at least two Southern states, including Alabama and Louisiana.

“One of the interesting things  (UC plant pathologist) Mike Davis has found using newer biotech approaches to more quickly identify disease is that other races in Southern states look pretty scary — a lot worse than Race 4. And they do not need nematodes to spread,” said Hutmacher.

This heightens the need to continue screening for soil borne pathogens as well as to focus on developing disease-resistant new varieties.

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