In the past week, sorghum ergot has been detected in several locations in Kansas, primarily in forage sorghum fields, but also in grain sorghum. This is a relatively rare event, with notable prior occurrences in 1997 and 2017. Sorghum ergot in the U.S. is caused by the fungus Claviceps africana. Claviceps africana has been reported in Australia, Central America, North America, South America, and South Africa. Sorghum ergot is not the same pathogen that causes ergot in wheat (Claviceps purpurea).
Sorghum ergot development
This fungus, Claviceps africana, infects unfertilized sorghum ovaries, resulting in no development of grain. Pollen present at the same time as ergot inoculum usually prevents ergot infection because pollination occurs much more quickly. The absence of pollen in male-sterile sorghum forage fields makes them extremely susceptible to infection by C. africana when both the pathogen and a favorable environment are present. Sorghum ergot can also be a problem if pollen is somehow absent or ineffective at the flowering stage. This can occur if the plants were subjected to cool, moist conditions prior to or during the flowering period. Anything that reduces pollination increases the potential for ergot infection.
Studies have shown a higher risk of sorghum ergot infection when minimum temperatures are ~53°F. Additionally, the chance of infection decreases when temperatures are above 75°F prior to flowering. However, cycling of the pathogen in variously-aged male-sterile forage sorghum fields under extended wet periods can occur at temperatures well above 75°F. Lack of pollen in these fields can be associated with rapid disease development and increased conidial (spore) spread across multiple fields. That may be a major factor in 2025 compared to previous years, as might be the large increase in acres planted to male-sterile sorghums.
Symptoms and Dispersal
Sorghum ergot is a grain replacement disease that creates two major problems.
- First, infection of non-pollinated ovaries precludes normal seed-set or development. Thus, infections are directly responsible for grain yield losses.
- Secondly, seed developing adjacent to infected florets often become contaminated with sugary, sphacelia honeydew, which is a sweet, sticky, amber-colored fluid (Figure 1).
The honeydew can also spread into other plant structures and leaves below the developing head. Honeydew is typically observed 7 to 10 days after initial infection. The honeydew consists of liquid and conidia (spores) that exude from diseased florets and are most visible during cool, damp weather. Honeydew production might affect grain and forage sorghum quality, but it is not associated with alkaloid toxin production, which occurs only in sclerotia. Once sphacelia production is complete, and especially when honeydew production has ceased, there is no risk of sclerotia production. Later-blooming male-sterile forage sorghums or late tillers may have a slightly increased risk of sclerotia production due to increasingly lower temperatures, but we have not observed any production in current fields.
Figure 1. Forage sorghum head infected with Sorghum Ergot in Ness County, Kansas.
Figure 2. Honeydew has dripped from the plant onto the soil surface. Photo taken in Ness County, Kansas.
Honeydew contains three types of conidia: macroconidia, secondary conidia, and microconidia. This honeydew also supports the growth of saprophytic fungi/molds, which can affect forage and grain quality. These seeds are of poor and downgraded quality and, because of their stickiness, may be difficult to remove during harvest. Honeydew may be disseminated from flower to flower by insects, rain, and wind. Aerial dispersal of conidia over long distances is believed to be the primary source of inoculum.
The formation of sclerotia by Claviceps africana has rarely been observed under field conditions in the United States. Sclerotia production requires low temperature conditions and is associated with the production of ergot alkaloid dihydroergosine. Johnsongrass, volunteer sorghum, and likely feral sorghums, such as shattercane, are also important for maintaining viable inoculum in the fields.
Management considerations
- Fungicide applications at this point in time will not be effective.
- Harvesting of sorghum, for grain or silage, may prove difficult due to the sticky nature of the honeydew.
- If portions of the field are more severely affected than others, producers may consider not harvesting that portion of the field or keeping the resulting hay lots separate for future testing.
- Delaying harvest until after a rain or freeze can help reduce the amount of honeydew on the plant.
- Honeydew can cause mold formation in baled hay or silage. Mold formation will reduce feed quality and can form mycotoxins.
- The presence of alkaloids, which are a toxic concern for livestock feeding, is reliant on the production of sclerotia. At this time, sclerotia production has not been verified in Kansas fields.
We are continuing to monitor this situation and evaluate the infections present in Kansas. Additional information on sclerotia and alkaloid production, as well as their potential effects on feeding and appropriate forage sampling procedures, will be included in a future eUpdate article.
Please help us track sorghum ergot!
You can contact Rodrigo Onofre directly at 785-477-0171 if you suspect a field has sorghum ergot and/or submit a sample to the K-State Plant Disease Diagnostic Lab at https://www.plantpath.k-state.edu/extension/diagnostic-lab/documents/2021_PP_DiseaseLabChecksheet.pdf.pdf. This will help us monitor the situation in the state.
Additional resources
Texas A&M Sorghum Ergot Factsheet:
https://southtexas.tamu.edu/files/2023/05/sorghum-ergot-new-disease-threat-to-the-sorghum-industry.pdf
UNL Sorghum Ergot Factsheet: https://cropwatch.unl.edu/plant-disease/sorghum/ergot/
SORGHUM ERGOT: Distinguishing Sphacelia and Sclerotia of Claviceps africana in Seed:
https://cdn-de.agrilife.org/extension/departments/plpm/plpm-pu-021/publications/files/sorghum-ergot-distinguishing-sphacelia-and-sclerotia-of-claviceps-africana-in-seed-.pdf
Rodrigo Onofre, Row Crop Pathologist
onofre@ksu.edu
Lucas Haag, Agronomist-in-Charge at Tribune
lhaag@ksu.edu
Jeanne Falk Jones, Northwest Area Agronomist
jfalkjones@ksu.edu
Logan Simon, Southwest Area Agronomist
lsimon@ksu.edu
Tina Sullivan, Northeast Area Agronomist
tsullivan@ksu.edu
John Holman, Cropping Systems Agronomist
jholman@ksu.edu
Brent Bean, Agronomist, United Sorghum Checkoff
Gary N. Odvody, Extension Plant Pathologist, Texas A&M University