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.