Southwest grain sorghum producers making a late crop should be on the lookout for ergot, a disease organism that attacks unfertilized ovaries and creates honeydew that may cause harvest and storage problems.
“Look for it, but don’t panic if you see it,” says Dr. Jeff Dahlberg, research director, National Sorghum Producers, Lubbock. “Wait until a freeze to harvest. Freezing temperatures knock it out.”
He said a light rain also may wash off the honeydew. “If growers can get in quickly following a light rain they may be able to harvest.”
Dahlberg said ergot typically causes no serious problems with sorghum in commercial fields. “We see it mostly in seed production fields. If pollination is off, we could see problems. Degree of infestation depends on weather. Ergot likes high humidity and fairly warm temperatures.”
He said cool temperatures and overcast skies in late summer, linked with a lot of late sorghum, could have created an environment that impaired pollination and one conducive to ergot in farm fields.
“Late fields that do not pollinate correctly may be vulnerable. If plants pollinate and are fertilized properly, there is no problem with ergot. We’ve had no reports in commercial fields, but we have seen some in production fields.”
Dahlberg said farmers would see some yield loss with poor fertilization. “Even without ergot, cold weather can pull test weights and yield down. With ergot, we see a big mess with the honeydew.”
He said the sticky secretion can cause combines to gum up and can create storage problems. “Don’t harvest when honeydew is on the plants.”
Honeydew drips out of the grain sorghum and onto leaves and the ground. “It may look like bird droppings.”
The sugary honeydew also creates an ideal environment for other pathogens. “Secondary pathogens come in on the sugar. In a worst case, panicles can turn black.”
Dahlberg said production field managers may spray fungicides to control the disease but that may not be feasible in commercial fields. “Complete coverage of the panicle is difficult to achieve, even in seed production fields.”
Ergot has no known toxicity to animals. “But I wouldn’t put animals in a field with heads that have turned black,” Dahlberg said. “Other pathogens will be on the honeydew.”
He said elevators will take the grain from ergot-infested fields. “It does not spread seed to seed, so it’s not a feedgrain issue. It can overwinter, but some studies indicate it is not very robust.”
Ergot also infects Johnsongrass and shattercane and could overwinter on these weeds. “In the High Plains, we are more likely to see ergot come in from down south on the wind. If we see infested fields this year we are not likely to see more next year from this infection.”
It can spread rapidly, however. Dahlberg said ergot was first detected in the Americas in 1995, in Brazil. In just two years, it had spread to the United States, into South Texas. “That’s a long way for it to travel in just two years. Just one infected plant, under the right conditions, can spread the disease all over.”
Dahlberg said the disease travels primarily by macroconidia (spores) that lodge and develop in unfertilized ovaries. He said the condition may “look ugly” but should not cause significant loss.
Researchers and breeders around the world are looking for management techniques and resistant hybrids. “A hybrid with good fertility is less likely to host ergot; hybrids with low fertility are more likely to get it.
“It’s a big annoyance and a huge aggravation if farmers try to combine ergot-infested fields. But this year we are more concerned with low test weight. That’s what folks may be docked for this fall.”