Consider variety selection, resistance management and product placement in your efforts to combat disease.
By Amanda Huber
What disease management lessons from 2015 can producers take into 2016? Two issues from last year involving leaf spot and white mold offer precautions for disease management this year.
In the case of leaf spot, Bob Kemerait, University of Georgia Extension plant pathologist, gave the following example: Good, experienced growers had significant defoliation from late leaf spot in fields where premium fungicide programs had been used.
“They found severe premature defoliation from late leaf spot in fields where strong fungicide programs were used,” he said. Yield losses of 30 to 40 percent resulted from this defoliation.
“These producers were not cutting corners. No using reduced rates. No using inexpensive products to make up for the costs of growing peanuts.”
In looking for an explanation, Kemerait says the first thing that was determined was that severe defoliation did occur in one specific variety that had susceptibility to leaf spot.
“In 2015, it was TuffRunner™’511’ and the year before, it was Georgia-13M,” he says. “There is not anything wrong with these varieties, but both of them are more susceptible to leaf spot.”
The second factor Kemerait found was that although strong fungicide programs were used, the programs were all built around strobilurin products.
“I cannot say or confirm that there is resistance to strobilurins at this time, but I can say that on June 14, 2014, azoxystrobin, our go-to strobilurin, went generic, which means more and more of it is being used.
“This is an at-risk fungicide that is very popular in corn, soybeans, peanuts and now cotton,” Kemerait says. “If it’s overused, no one is surprised if we begin to see a combination of more susceptibility and a problem with resistance. That’s why we are seeing more premixes and tankmixes with other products.”
White Mold Weather
In 2015, very warm temperatures drove severe epidemics of white mold, and many affected fields were non-irrigated.
“Temperatures were phenomenal for white mold,” Kemerait says. “Conditions were wet in the early season, which means rank vine growth. In mid-to-late season, it was dry, but there was enough moisture to trigger white mold. Infrequent rains meant that fungicides were not being moved down into the crown of the plant and to the soil line.
“I don’t point the finger at the fungicide,” he says, “I point it at the kind of year we were having.”
The key to managing white mold is all about fungicide placement. Getting fungicides where they need to be during the initial deposition might involve increased spray volume, increased pressure or revisiting the need to spray at night or in the early morning when the leaves are folded up and the fungicide is more likely to move down into the target area of the plant, says Kemerait.
“Irrigation or a rainfall within 24 hours of a fungicide application is our recommendation,” he says.
“For a lot of these products, irrigation as early as 12 hours is recommended.”
For 2016, remember that variety selection, fungicide overuse and fungicide placement interact with weather to drive disease expression in the field. Attention to details and timeliness are the producers best plan of action.