Issue No. 22, Article 2/September 21, 2012
End-of-Season Disease Issues
As we are getting closer to the end of the growing season, there are still some disease issues and questions that should be addressed.
Aspergillus ear rot and aflatoxin. As I noted in the August 10 issue of the Bulletin, Aspergillus ear rot is present in some Illinois drought-stressed corn fields. The biggest concern with the disease is that the fungus that causes the ear mold may also produce a toxin known as aflatoxin. Corn with aflatoxin levels over 20 parts per billion (ppb) may be docked or rejected at the elevator. As discussed in the August article, it is extremely important that producers be aware that their corn could be contaminated with aflatoxin. An Aflatoxin section is now available on the University of Illinois Extension Illinois Drought Resources website, including a new "Frequently Asked Questions about Aflatoxin in Corn" document.
Black mold and dust clouds during harvest. After some significant rain in late August and early September, saprophytic fungi, which have a black appearance, have colonized dead corn tissue in some areas of the state. In corn that was drought-stressed and died prematurely, these molds rapidly colonized dead tissue after rains fell. Black clouds of dust, the result of the saprophytic fungi, have been observed as combines go through affected fields. Generally, there is no concern with these saprophytic fungi other than more dust than normal to deal with, which may mean having to clean filters on the combine more often.
Soybean rust. To date, no soybean rust has been observed in Illinois in 2012. However, it is likely that Hurricane Isaac did bring some spores of the soybean rust fungus as it moved through Illinois a few weeks ago. Given the current stage of the soybean crop, risk of yield loss to soybean rust would be extremely low, so even though soybean rust may be observed in Illinois this year, no management this year is required.
Soybean rust observations in North America as of September 18. (Source: sbr.ipmpipe.org.)
Soybean vein necrosis virus. Symptoms of soybean vein necrosis virus have been prevalent throughout the state. As Suzanne Bissonnette wrote in the August 24 issue of the Bulletin, the virus is a recently described virus of soybean. It is likely that it is transmitted by thrips, since other viruses in the same group (Tospoviruses) are, but more research is needed to confirm the transmission method. Because this virus is newly described, no information is available on yield loss potential and management.
Symptoms of soybean vein necrosis virus on soybean leaflets.
--Carl A. Bradley
Carl A. Bradley