Sorghum Ergot - What Is It?

DR. BRENT BEAN

LUBBOCK, TEXAS

Every year is always different, and certainly 2025 has not been the exception to the rule. Much of the U.S. sorghum belt experienced wetter and cooler temperatures than normal. While these conditions did produce good yields, it also opened the door for ergot infection, a disease we have seen very little of in recent years. Although not that many acres were infected, ergot could be found in both forage and grain sorghum fields over a wide region. 

What is Sorghum Ergot?

Sorghum ergot is a fungal disease caused by Claviceps africana and is easily identified by the production of honeydew, a thick, sticky exudate that drips from the infected sorghum heads onto surrounding leaves and the ground. It is important to note that this is NOT the same ergot that infects other crops, such as wheat and fescue. 

Infection and Spread of Ergot

The infectious cycle of ergot occurs during the sorghum plant's flowering period, which typically lasts from three to seven days immediately following heading. During this time, non-pollinated florets are vulnerable to ergot infection. Any conditions that are present that reduces pollination increases the potential for ergot infection. Once an individual floret is pollinated it can no longer be infected with ergot. A typical sorghum head contains hundreds, and sometimes thousands of individual florets. Once infected, the fungus produces an abundance of honeydew that contains spores capable of being transported by the wind, enabling the disease to spread over long distances. 

Susceptibility of Sorghum Varieties

Sorghum varieties differ widely in their susceptibility to ergot. Commercial grain sorghum hybrids exhibit high resistance to infection owing to their abundant pollen production. In contrast, male sterile forage sorghum and seed production fields are much more vulnerable due to the lack of pollen being produced in the female parent line. 

Toxicity Concerns

In forage sorghum grown for silage or hay, one of the frequently asked questions revolves around whether ergot poses a toxicity risk to livestock. Honeydew contains only very small alkaloid amounts, posing little risk to livestock. It's important to clarify that the alkaloid toxins associated with ergot in other crops such as wheat or fescue differ significantly from those produced by C. africana in sorghum. 

Harvesting Challenges and Management Strategies

Harvesting can become complicated when honeydew is present in large quantities, as it may clog harvest machinery, necessitating time-consuming cleaning processes. The honeydew is water-soluble, which means that significant rain or irrigation can wash it away, and a hard freeze effectively kills the sorghum plant, eliminating its food source to produce honeydew.

Farmers can employ several strategies to manage and reduce the risk of ergot infection. These include avoiding planting during periods likely to result in poor pollination and steering clear of late planting that could coincide with cooler nighttime temperatures during flowering. Avoiding male sterile forage sorghum varieties or harvesting them prior to, or soon after, heading will eliminate the risk of ergot infection. 

Fungicide Applications and Winter Survival

It's noteworthy that while fungicide treatments can be effective, their timing is crucial. Fungicides should be applied just before flowering for optimal results, with complete coverage of the sorghum heads necessary for effective prevention.

As for winter survivability, sorghum ergot does not withstand freezing temperatures experienced in regions like the High Plains; however, in milder southern climates, some inoculant may survive and pose a risk to new crops in subsequent growing seasons.

Conclusion

Fortunately, widespread ergot infection in sorghum is a rare occurrence in the United States. The last time ergot was this widespread was in 1997. Although it is not unusual to occasionally see a few infected plants, hopefully it will be another 28 years before it is this prevalent again.   ∆

DR. BRENT BEAN

UNITED SORGHUM CHECKOFF AGRONOMIST