Odds are low for grain sorghum disease, but still scout

Frances Gould, Gautreaux, Craig  |  8/14/2015 8:25:46 PM

Trey Price, a plant pathologist with the LSU AgCenter, recommends fields of grain sorghum be scouted at least weekly throughout the growing season. Anthracnose is the most common disease found in Louisiana grain sorghum. Photo by Olivia McClure

Photo By: OLIVIA MCCLURE

While disease can wreak havoc on soybean or cotton crops, grain sorghum may be less likely to suffer from a disease outbreak. Trey Price, a plant pathologist at the Macon Ridge Research Station in Winnsboro, said the odds are low that a grower will have to make a fungicide application for disease control in grain sorghum most years.

This does not mean growers should neglect their fields. "I would still recommend that growers or their agricultural consultants inspect their fields at least once a week throughout the growing season," Price said.

The earlier a disease pathogen infects a field, the more susceptible the crop is to yield loss. Grain sorghum is most sensitive to yield loss because of lost foliage during heading. The closer the crop is to maturity, the more foliar damage it can take.

Anthracnose is the most prevalent disease found in sorghum, Price said, adding that losses of up to 20 percent have been noted.

"In some years, we will see yield loss from anthracnose, more so in the central and southern part of the state. The disease is more likely to be found in late-planted sorghum," he said.

In 2014, Price had 10 field trials across the state examining grain sorghum diseases. In 2015, he has six trials in three locations – three trials at Macon Ridge, two at the Northeast Research Station near St. Joseph, and one at the Dean Lee Research and Extension Center near Alexandria.

"We don’t have a lot of fungicides available to treat for diseases. However, the fungicides we do have are effective on some of the foliar diseases," Price said.

Price strongly believes that producers should only apply fungicides when absolutely necessary.

"Fungicides are expensive to apply. There really is no need to make a blanket or automatic application. You have to make certain the economics work," he said.

One recent concern for sorghum growers has been the sugarcane aphid. In addition to damaging plants, the honeydew it creates clogs combines and causes harvest problems.

"It is probably more feasible for farmers to save their money on fungicides and budget those funds for additional insecticide application if the aphid presents a problem," Price said.

While grain sorghum is known for its drought tolerance, irrigation may help stave off disease. "Water is the No. 1 limiting factor in agriculture when it comes to yield. A less-stressed plant will resist diseases much better than a stressed plant. Irrigation will likely increase yield and may offset many losses attributed to disease or help prevent it."

Two other diseases that may be found in sorghum fields are corn leaf blight and gray leaf spot. Scouting for these and other diseases is difficult because they appear similar. Also, there can be many other causes of foliar damage.

Price recommends that if a producer suspects a disease, the producer should contact the local parish extension agent. The agents are familiar with the protocols of handling potential infections and getting them accurately diagnosed.

"Crop rotation and, in some cases, tillage can also reduce the risk of disease. More importantly, make management decisions on a field-by-field basis. Take into account the crop stage, the severity of the disease, the prevailing environmental conditions and the expense of applying a treatment versus the economic return. Fields do not have to look perfect in order to be profitable," Price said.
Craig Gautreaux

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