The combination of aerial imagery and discovery of an effective fungicide has provided many Texas cotton farmers with the first opportunity in a century to manage cotton root rot effectively and economically.

When Chenghai Yang, with the USDA Agricultural Research Service in College Station, started using aerial imagery to map root rot infections back in 1990, he discovered that he could identify where the disease was located, map the fields accurately and follow progression of the disease throughout the field and across seasons.

“But we had no effective control,” he said during a presentation at the Concho Valley Cotton Conference in San Angelo.

Tom Isakeit, Texas AgriLife Extension pathologist, has been looking for an effective control strategy for years, with little success until recently. His research led to an emergency exemption last year for Topguard fungicide. That exemption has been continued for 2013 with some modifications.

The two discoveries may allow farmers in the cotton root rot zone—mostly in the heavy soils areas of Texas, to use an effective fungicide and perhaps target applications to eliminate the need to apply materials to entire fields.

“Aerial imagery and mapping will make fungicide use more effective. We can treat only the infected areas of a field,” Yang said. “By identifying the infected spots we can use GPS technology to apply fungicide to only a small percentage of a field. In some cases, we may determine that it’s more economical to treat the entire field.”

His research has shown root rot maintains a fairly stable area of infection in a field. “Research has provided a better understanding of the development and progression of the disease,” he said.

“Now, we can also monitor the efficacy of Topguard.”

“Aerial imagery and mapping allows us to predict where we need to treat,” Isakeit said.

Yang has used a four-camera system, including blue, red, green and near-infrared imagery to monitor progression of root rot. Newer technology uses one camera that covers 3.4 miles by 2.3 miles at 10,000 feet. He’s also using Cessna 206 or Cessna 404 aircraft.

He can overlay maps from 2001 through 2011 to show the progression of root rot in specific fields. “The disease varies some from season to season but the infection area remains fairly consistent. That gives us confidence to use the technology to target treatments. Imagery spanning 10 years shows infection in basically the same locations.”

More recent imagery and monitoring, Yang said, “shows that Topguard works.”

“It looks like we finally have a solution to cotton root rot (CCR),” Isakeit said. “We will continue to conduct research, however. Focus will be on different application methods such as in-furrow and over-spray.”

In-furrow treatments are included on the emergency exemption label for 2013. “We need more research on overspray options,” Isakeit said. He’s also pursuing testing on stem spray, a practice that he’s seen work in past trials. He said devices to apply the material onto lower stems are available. Field conditions, however, might be an issue as equipment bouncing could create application problems.

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“We also will continue to monitor phytotoxicity. Seed is vulnerable just before emergence. But we need the right conditions to assess efficacy and phytotoxicity. In 2012, it was too dry. We had no root rot. With irrigation we can monitor how Topguard is supposed to work.”

To be effective, Topguard needs rainfall or irrigation three to five days after planting. “Even a delay of one month will still be somewhat effective, but if the field receives less than two inches of rain in a month after planting the application will not be effective.”

Also, if a lot of rain falls within three days of planting, phytotoxicity is more likely.

“We will continue to test untreated areas to compare results,” Isakeit said.

Grower responses are positive

Grower reports from the first year of use have been positive. “They say control looked good. We have had some issues with lack of experience with the product. But responses also show that control more than made up for the cost of the fungicide. Also, we had reports that cotton strippers did not clog up during harvest. That is a valuable benefit.”

Isakeit said Texas AgriLife testing in the Lower Rio Grande Valley has not panned out in recent years because of extended drought. “Other tests in the area have shown efficacy, however. The most effective way to monitor Topguard is under conditions that are conducive to disease—wet weather.”

He reminds growers, however, that the decision on Topguard use must be made long before they know what weather will be like. Current label permits only at-planting applications.

Modifications for Topguard application this year include a narrower T-band width, as well as in-furrow application. The label says the material should have no direct contact with the seed. Also, application through irrigation is not allowed, and a 365-day plant-back restriction applies to crops except cotton, corn, peanuts or soybeans. Recommended rate is 1 to 2 pints per acre at planting.

Persistence in the soil should not be a problem at labeled rates, he said, with the caveat that using the higher rate could be problematic in a monoculture.

“We also recommend an IPM strategy,” Isakeit said. “Crop rotation is still important since fungicide resistance is possible. But resistance is likely to occur slowly if the fungicide is not constantly used.”

Monoculture production creates other problems as well. “Monoculture can lead to other problems that are much more difficult to deal with.” Root knot and reniform nematodes are possibilities that “build up in monocultures.”

Future research will include the possibility of a more concentrated liquid formulation from the manufacturer, Cheminova, and the possibility of adding application through subsurface drip irrigation to the label.

Isakeit said the things that keep him up at night now are the possibilities that things will go awry through off-label use on other crops—partly because of the soil stability of the fungicide.

Also a concern is that farmers may abandon the product if it doesn’t live up to standards—if it’s inconsistent or inefficient—issues that do not seem to be occurring in initial applications. Phytotoxicity is another concern. “The product is not perfect, and we still need to tweak it some,” he said. “But we know enough to understand what causes phytotoxicity. Seedling damage is possible if the product comes in direct contact with the seed.”

He said tests that looked at Topguard use on other plants and other diseases have not been successful. “Soilborne diseases are tougher to deal with.”

A graduate student has been looking at soil conditions as a possible predictor of root rot infection. “He’s studied electro-conductivity, texture, pH and other properties, but he has not found anything,” Isakeit said.

“We want to use an in-season plant sensor to monitor changes in leaf reflectance. But we still go back to needing a map. That’s where Yang’s efforts will pay dividends.”

“Root rot has been a destructive disease for Texas cotton growers for the past 100 years,” Yang said. “And they have had no effective control until recently.”

Isakeit said research back in the 1920s found formaldehyde to be somewhat effective in knocking back root rot infections. “But it is a nasty application,” he said.

“A lot of farmers used Topguard in 2012,” Yang added.

And, based on reports, success was noteworthy. With that start, Isakeit’s continued efforts to make the product even more efficient and Yang’s ability to plot progress of the disease, efficacy of the fungicide and target hot spots in the field, farmers may now have the solution that has eluded them for the past 100 years.

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