San Joaquin Valley cotton growers’ aggressive effort to turn back a menacing soil fungus that threatens to take out significant future crop acreage has suffered a major setback.

Earl Williams, president of the California Cotton Ginners and Growers Associations, informed association members recently that it is highly likely the USDA Research Station in Shafter, Calif., will close down and with it will go two key researchers working on impeding the deadly fungal disease Fusarium Race 4.

The station first appeared on a USDA closer list several months ago when SJV cotton growers mounted a strong effort to keep it open, soliciting the support of many agricultural groups in the state and lobbying USDA and Congress.

Early on, Williams said there was a 50-50 chance this lobbying effort would be successful. Recently, the final closer list was released, and Shafter is still on it.

Williams said working to keep it open has not stopped, but he said there is only about a 10 percent chance the historic station will remain open.

It has become so obvious the station will close that USDA refused to allow USDA-ARS research plant pathologist Rebecca Bennett and research geneticist/plant breeder Mauricio Ulloa to meet with the grower/industry Fusarium Race 4 group working to discuss their most recent research on Fusarium.

“It is absolutely ridiculous” is the way Williams described USDA’s response to growers and others to gain the latest information from these two researchers in the wake of the station closing or to perhaps hand it off to University of California researchers working on the same Race 4.

Williams told producers at the recent PhytoGen grower meetings that USDA has indicated it might move the research to another USDA research station, possibly in Mississippi. However, he is skeptical.

“Mississippi cotton growers do not want Fusarium research in their state,” said Williams. “The problem is in California and that is where the research should be conducted.”

What is even more frustrating is that the Fusarium Race 4 working group is targeting the problem with strong financial support for research coming from the California Cotton Alliance, California Crop Improvement Association and State Support money from Cotton Incorporated. This money could go to continue support of the USDA research.

Williams said the working group is trying to preserve some of the research conducted at Shafter by shifting it to the University of California, Davis where another leading expert on Fusarium Race 4, Mike Davis, is working on the problem.

It was Davis who first identified the Race 4 in the early 2000s. It had probably been in the San Joaquin Valley since 1990.

Fields rendered useless

Unlike other fusarium races, Race 4 is not associated with root knot nematodes. It does not need them to vector the disease. It is the only fusarium that does not require nematodes to spread. Once it is in the soil, it is there forever and if inoculum levels reach high enough, a field can be rendered useless forever for cotton production.

Although it has been around for at least two decades, concerned dwindled among growers along with cotton acreage not long after it was found. SJV acreage declined to less than 200,000 acres in 2009. However, it did not go away; it just remained dormant until cotton returned to the fields. SJV cotton acreage has increased significantly over the past couple of years and with 450,000 acres in 2011, Fusarium Race reappeared with a vengeance.

It has been identified in at least 200 fields spread out over every single SJV cotton-producing county.

“It really showed up in 2011,” said Williams.

Cotton is the only crop Fusarium Race 4 impacts, but it remains virulent for decades in soil, once a field is infected with diseased cotton. It is spread primarily by soil on equipment, sprinkler pipe and irrigation water.

University of California Extension cotton specialist and agronomist Bob Hutmacher said processing tomato, lettuce and other vegetable harvesting operations on the West Side of the San Joaquin Valley are particularly problematic in spreading Race 4, since fields are muddy at harvest time and trucks and harvesting equipment carry mud onto roadways and into other fields.

Hutmacher recommends:

  • Pressure wash implements, sprinkler pipe, machinery from farms even suspected of having Race 4.
  • On known Race 4-infected fields, avoid land planing or other leveling that moves soil and consider reduced, conservation tillage in those fields.
  • Restrict irrigation tail water movement off infested fields.
  • Limit equipment traffic through Race 4 infested areas of fields.
  • Limit land planing to prevent spreading infected soils to clean areas of a field.
  • Don’t spread gin trash from infected fields to clean fields.

Resistant varieties are key

Experts agree that the key to turning back Fusarium Race 4 is the development of more, higher resistant varieties. That is why the closure of Shafter and the apparent departure of Ulloa are particularly disappointing. Ulloa has made significant progress toward identifying Fusarium Race 4 resistant genetics.

UC has screened both existing Pima and Acala varieties for susceptibility to Race 4. Initially, most believed Race 4 would only impact Pima. However, that has proven incorrect as the fungal inoculum has magnified in field and Acala varieties are considered susceptible. The UC cotton management website: http://cottoninfo.ucdavis.edu/pubs.htm contains fusarium variety screening trials to help growers select varieties for Race 4 infected fields.

Planting highly susceptible varieties in infected fields is a virtual guarantee that Race 4 will spread rapidly.

A grower might get away with planting a susceptible Acala or Pima for a one or two seasons in lightly infected fields, but eventually Race 4could render the field unable to produce cotton. Several growers have already red-lined fields for cotton because of high Race 4 inoculum levels.

Hutmacher said the most tolerant and most susceptible Pima varieties are Pimas with Acalas “somewhere in between” the Pima range.

PhytoGen 800 has been a lifesaver in the Race 4 challenge. It is the most resistant variety available. The new PhotGen 802RF is right up there with 800 on resistance. However, Dow AgroSciences rep Harry Peck said the Roundup Flex variety will be on “allocated,” limited supply in 2012. 800 planting seed should be plentiful, he added.

Until more resistant varieties are developed, Hutmacher said the first line of defense is to reduce Race 4 inoculum.

The first step is to monitor for the diseases. UC and the grower organization have developed an excellent brochure on what to look for in scouting for fusarium. It is available at http://cottoninfo.ucdavis.edu/IMAGES/Fusarium.pdf.

Sampling for Race 4 in cotton row skips or sickly plants is the first place to check for fusarium. Hutmacher recommends killing any surviving, weak plants, even if they hold the potential for setting cotton.

Major threat

He says leaving those plants for their limited yield potential is not worth the risk of spreading millions of Fusarium Race 4 spores across a field from infected plants.

“It is probably not necessary to take the plants completely out of the field as you would with dodder, but make sure the plants are dead after you pull them out of the ground,” he said.

“I would hate to see someone pile a bunch of infected plants in the back of a pickup and then dump them somewhere else on the farm where Race 4 might be spread,” he said.

Getting fields off to a good start is another way to reduce Race 4 spread. Later planted cotton seems to fare better than cotton planted early under less than ideal conditions, he said.

“The fewer challenges a plant has to grow off quickly, the better chance it has to stave off Fusarium Race 4,” Hutmacher says.

Hutmacher said disease-preventing seed treatment is also a good investment against Race 4. The UC cotton research team will be looking at seed treatments specifically for Fusarium Race 4 control, as well.

Soil solarization/tarping fields in the summer to heat up the soil to reduce the inoculum is a proven method of reducing Race 4 inoculum. However, it is not always practical in the San Joaquin Valley where summer fallow is not economically acceptable in high value, irrigated agriculture.

However, summer fallow without tarps could be an option in a drought year like 2010 when irrigation water supplies were limited.

“A grower on the West Side planted two different fields to the same cotton variety at the same time in fields where Fusarium Race 4 has been identified. The only difference was that one field had been summer fallowed the year before because of limited water supplies and the other had not,” he said. “The difference between the two fields was obvious.”

The Race 4 threat is so serious many growers are trying to control it without much research to back their efforts. This has included roguing small, infected areas, injecting soil fumigant and then tarping. Another grower injected Vapam through sprinklers to a limited, infected area with good results.

In Australia, where Race 4 was identified earlier than in California, growers leave defoliated, harvested cotton stalks standing for 30 days before shredding and disking to reduce inoculum in the soil. This may not be practical in the San Joaquin Valley, due to plowdown regulations to control overwintering pink bollworm.

“A lot of what we are seeing growers do now here in California is anecdotal, but in many cases it seems to be working. We are looking forward to researching more thoroughly what growers are doing on their own,” he said.

“Regardless, we are seeing a lot of cooperation and support from growers as we tackle this problem” said Hutmacher.

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