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Preliminary tests indicate potential for fungicide to control root rot

Cotton root rot has been a bane of Texas cotton producers for almost 100 years.

“Looking back through the literature we’ve found that USDA has been working on root rot management since 1917,” says Rick Minzenmayer, Texas AgriLife Extension integrated pest management specialist in Ballinger. “The fungal disease has been an issue for Texas farmers for a long time. Every year surveys indicate cotton root rot at the top of the list of concerns in Texas, Arizona and New Mexico, especially south of I-20 in Texas.”

Minzenmayer and San Angelo farmers John and his son Doug Wilde hope a fungicide being tested on the Wilde farm will render root rot a non-issue in the near future. It can’t come too soon for the Wildes, who lose cotton to the disease each year.

“Root rots results in lower yield, low mic and short staple,” John says. “Infected fields also take more time and labor.” Root rot kills cotton plants and with the ravaged root system stalks come loose from the soil during harvest and lodge in strippers, requiring operators to shut down the machines, get down and remove the stalks.

“Some of our fields are 50 percent infected,” Doug says. “With drip irrigation, we push for 4 bales per acre but in heavy infestations, we may get 50 percent of that.”

In the past farmers have tried rotation and deep tillage to break the disease cycle. “Corn helps,” Doug says. “We get organic matter from corn stalks and that helps with our conservation tillage, too.”

“But cotton is the cash crop,” John says. “We grow corn for rotation.” Farmers also rotate to wheat and occasionally grain sorghum to break the root rot cycle.

“Some have tried deep tillage, but that’s more expensive. Most of us are now doing less tillage.”

Minzenmayer and Tom Isakeit, Texas AgriLife associate professor and Extension plant pathologist, have been testing fungicides for several years to see if those with some efficacy in greenhouse experiments would work in the field.

“We screened nine products in 2008,” Minzenmayer says. “We know all had some activity in greenhouse tests. Tilt worked in some situations, but the company is not interested in pursuing a label for cotton. We’re also looking at new products coming on the market.”

One promising option is not new, but has not been used in cotton, Minzenmayer says. “Flutriafol has worked well. In 2008 we were looking for field efficacy and used some unrealistic rates to see if it would work. We’ll reduce rates to see how low we can go. We’ve seen good control with it.”

“It’s still experimental,” Isakeit says. “We have to get the rates really low so EPA will look favorably on it and so it will be economical for farmers. We also need more research on timing and methods of application.”

He says testing global positioning system technology will be important. “We want to take advantage of GPS technology so we can treat only areas of a field that need it.”

John Wilde agrees. He thinks farmers may tap into new technology to help apply the materials economically. “They can identify infested spots in the field one year and then use GPS to treat just those areas.”

John and Doug have test plots on their field this year for the second season and Minzenmayer says they will evaluate those after harvest to see if they can replicate 2008 results. “We’ve reduced rates on these tests.”

They also left some plots from the 2008 trials in the test, but did not treat them in 2009 to see if control was good enough to knock populations back for more than one year. “In the best of those plots, we saw no significant difference between them and the treated ones,” he says. “In one trial we saw no disease in the 2008 plot and the (untreated) row just 40 inches over had 50 percent dead plants. We’re not calling it carryover and are not yet sure why we have control the second year.”

They have identified some side effects from extremely high rates with “phytotoxicity 40 days after treatments. But we took those plots to harvest and found no significant yield difference from the untreated check,” Minzenmayer says.

“We haven’t identified the optimum application rate yet, but 0.0625 pound will be the low end and we think 0.125 pound will be a good starting point. We may test up to a half-pound per acre in 2010. At these rates, we’ve seen no side effects.”

Rates will be important for producers. “We have to keep the cost down so treatment will be economical for farmers,” Minzenmayer says. “At 0.125 and current price for the product, cost is about $21 per acre.”

Flutriafol is not labeled for cotton yet. Cheminova owns the product and “is in the preliminary stages of registration. We know it works. We still need to stabilize rates and do residue studies,” Minzenmayer says.

Next step will be to evaluate lower rates and application techniques. “We’ll look at granular applications in 2010 and other formulations. We want to be able to use it on dryland as well as irrigated acreage.”

Doug and John Wilde are testing the product in drip irrigation fields and apply the material through the system. They have about 500 acres of cotton on subsurface drip irrigation. “We have no pivots,” John says. “We converted from furrow irrigation to drip. And we still have some dryland cotton.”

“This product is so new we’re still scratching our heads trying to figure out the best way to use it,” Minzenmayer says. He says the material is “apparently quite stable.”

Randall Conner, executive director of the Southern Rolling Plains Cotton Growers Association, says farmers in the region are “excited about what Rick and Tom are doing.” The association is one of three partners helping to fund the project, along with the Cotton Incorporated Texas State Support Committee and Texas AgriLife Extension. Conner and Minzenmayer also expressed appreciation to Doug and John Wilde for making fields available for the study. Minzenmayer says cooperation requires a lot from growers. John says the project gives him and his sons (another son, Matthew, also farms in the area) an opportunity to see firsthand how the product works under field conditions.

Minzenmayer says the tests will continue through 2010 at least. “The company will pursue registration but we’re not sure how soon that will be.”

John says they know the product will work and are anxiously waiting further tests and a label. “We need more information on rates and application rates.”

“Farmers in this area are excited about the possibilities,” Doug says.

Isakeit cautions growers about using the product prematurely. “It’s not yet recommended. It’s not labeled. And we need more work,” he says.

“We’ve had no breakthroughs on root rot control for a long time. But we’ve had trials in different parts of the state with both sidedress and drench applications.”

He says a test at the Stiles Farm, a research facility in Thrall, showed results equally as good as those on the Wilde farm. “We saw a dramatic difference between treated and untreated plots,” he says.

Isakeit says preliminary data from the Wilde farm also shows “a huge difference in yields between treated rows and the untreated checks.”


TAGS: Management
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