Posted 6 October 2008. PMN Crop News.
Cool Weather Brings Threat of Sorghum Ergot
Kansas State University. www.ag.ksu.edu
Manhattan, Kansas (September 17, 2008)--Honeydew could begin dripping from grain sorghum and forage sorghum heads in Kansas this year, according to a Kansas State University scientist. The cause: sorghum ergot.
This disease occasionally causes problems in very late-maturing grain sorghum and on male-sterile forage sorghum in the Central Plains, said K-State Research and Extension plant pathologist Doug Jardine.
Why the concern this year?
"The combination of cool nighttime temperatures and late-flowering sorghum in late August and early September is the reason," Jardine said. "Cool nighttime temperatures inhibit pollination and create an avenue of infection for the organism."
Sorghum ergot infects the ovaries of sorghum flowers and often converts them into a white, fungal mass. The most obvious external symptom of infection is the sticky honeydew that often drips onto the leaves and soil, he said.
"Sorghum ergot infects only unfertilized ovaries. Once fertilized, an ovary becomes resistant to infection. Any condition that prevents or delays fertilization increases the risk of ergot," he added.
Sorghum plants with inherent male sterility or with pollination difficulties caused by cool temperatures are most severely affected by ergot.
Once an infection has occurred, there is nothing producers can do to cure the disease, Jardine said. The only thing producers can do at that point is devise a management plan for trying to avoid the problem next season.
"To minimize the development of ergot and limit its impact, producers should try to avoid late planting next year," he said.
The goal is to avoid low evening temperatures (below 55 degrees F) during the period three to four weeks prior to flowering and from flowering to five days thereafter. Fields that bloom in July and August seldom, if ever, have problems with ergot, the plant pathologist said.
Photos of sorghum ergot are available in the publication, "Diagnosing Sorghum Production Problems" S-125 at: www.oznet.ksu.edu or at county and district K-State Research and Extension offices.