The disease of real concern to North Carolina sorghum growers is anthracnose, which has appeared every year in the state since North Carolina State University started working with the crop, according to Dr. Randy Weisz, North Carolina Extension small grains specialist.
Anthracnose is a fungal disease that is common in sorghum in this wet and humid region, Weisz said. Weisz notes that preliminary research shows that yield loss in sorghum due to anthracnose can be as high as 15 to 30 bushels per acre. NC State is conducting fungicide studies to control the disease.
“This year the anthracnose isn’t so bad,” Weisz said. “Whether in another two weeks it’s going to come in and whack us, I’m not sure,” Weisz said at a sorghum field day Aug. 14 at the Upper Coastal Plain Research Station’s Fountain Farm in Rocky Mount.
“Anthracnose begins as red lesions on the lower leaves and stem. It moves up the plant, and when sorghum heads, it moves onto the peduncle (the stem that holds the head up),” Weisz explained “Once on the peduncle it, invades the vascular tissue. That weakens the peduncle which can lead to the head breaking off. It also blocks the flow of nutrients to the grain, so that yield and grain quality decrease,” he said.
“The real concern we have is when it gets on the peduncle. Once the sorghum heads out, this disease will rain splash onto the stems right below the head or the peduncle. The peduncle turns a purple color like you bruised it,” Weisz said. “When you have an infected peduncle, and you split it open, what you’ll find in a really bad infection is that infection has gone inside the peduncle and completely blocked up the vascular system. If you have a blocked vascular system going up into the head, that means that’s the end of grain fill.”
Last year, researchers used BASF’s Headline fungicide to control anthracnose, which offered good control when sprayed at early heading to first flower, according to Weisz. “Spraying either slightly later or slightly earlier, we didn’t get the control. So timing seems to be very important,” Weisz said.
This year, NC State is examining other fungicides in addition to Headline in its anthracnose research work.
“The good news is that we do have ways to control anthracnose, and I think there is a yield advantage of applying fungicide if it’s done in a timely way,” Weisz said.
Another concern for sorghum farmers in North Carolina is yield loss in wheat following sorghum. NC State is in its third year of research on wheat following sorghum, and Weisz notes that generally wheat yield loss is greatest in soils and conditions that produce high yields in both sorghum and wheat. He said yield reductions are close to 20 percent in these conditions.
On the other hand, in poorly drained soils that don’t produce as high a yield, research so far shows just a 4 to 5 percent yield loss in wheat following sorghum, Weisz explained.
There are several different theories for the yield loss, including root extracts coming out of the sorghum that are interfering with the wheat growth. NC State is conducting research states to get around this by using higher rates of preplant nitrogen on the wheat before planting.
“The theory is that we are turning under a lot of biomass from sorghum, and the nitrogen is getting tied up,” he said. Last year, researchers looked at rates as high as 60 pounds of preplant nitrogen.
Research is still preliminary in yield loss in wheat following sorghum, and Weisz said he is hoping to have more conclusive data this year on the benefits of higher rates of preplant nitrogen in wheat following sorghum. NC State is conducting tests on four locations across the Coastal Plains on different soil types.
“If you’re interested in wheat following sorghum, do everything you can to disk in that sorghum,” Weisz advises. “Do a really job with your tillage. Desiccate your sorghum. Kill your sorghum before you harvest it. Do everything you can do to achieve an excellent wheat stand.”
Weisz said proper seeding rates, planted at the right depth is also important. “Do everything you can to get the best stand of wheat,” he said. “Get your fertility right. Do not skimp on P and K and sulfur and nitrogen on your wheat if you’re following sorghum. Get a soil test done. Pick the highest recommended rate of preplant nitrogen.”