August 23, 2012
ISU EXTENSION DROUGHT WEB PAGE
ISU Extension is compiling resources on a web site to help you deal with the drought. Resources on the web site are provided under various categories: Crops, Livestock, Dealing with Stress, Home and Yard, Financial Concerns, and Tips for Businesses. More information is being added daily. Local educational events dealing with the drought can also be found on the page which is at http://www.extension.iastate.edu/topic/recovering-disasters.
Ear Rots & Aflatoxin
One of the concerns many have with this years drought is whether we are going to have aflatoxin problems. I have seen some Aspergillus flavis (the fungus that produces aflatoxin) on corn ears in the area, and have already heard of some loads of corn being rejected for aflatoxin, so we know there will be some problems with it this fall. A hot, dry August, especially with night temperatures in the 70s, is most conducive to the production of the toxin, so hopefully the rains that have come in August, along with the cooler temperatures will reduce the problems with this. It is important to check the corn soon to see if there is an ear rot problem and schedule those fields to be harvested first. The sooner the corn is dried down in the bin, the faster the mold growth and aflatoxin production is stopped. Aflatoxin production is greatest when the grain is 18-20% moisture, so harvesting before it gets down to 20% would be best. However, be sure to have the corn checked in the field by the insurance agent if you suspect a problem with aflatoxin. Once its in the bin its too late for insurance to get involved. Aspergillus flavis is an olive green mold. Just because the mold is present does not necessarily mean the toxin is present. For a photo of Aspergillus ear rot and additional information on this subject, go to: http://www.extension.iastate.edu/CropNews/2012/0801robertson.htm. ISU Extension has a publication that explains sampling, testing and interpretation for aflatoxin. Go to: http://www.extension.iastate.edu/sites/www.extension.iastate.edu/files/www/PM1800.pdf
I am also seeing fusarium ear rot on corn in the area, especially in fields that had some insect feeding on the ears by Japanese beetles, rootworm beetles, and western bean cutworm. This disease is also more common with hot, dry weather. It causes a white to pink cottony mold that is often at the tip of the ear or anywhere there is insect damage. This fungus produces the mycotoxin fumonsin.
Another unusual ear abnormality that is being found in some fields is kernel red streak, which causes red streaks on the sides of the kernels. It is caused by a toxin spread by the wheat curl mite, but is mainly cosmetic and doesnt affect the feed value of the corn.
Grain Harvest Considerations
Drought stress much of the summer has resulted in many corn fields with smaller diameter stalks and less brace root development than normal. This could make plants more prone to lodging this fall, although smaller ear development in many fields wont make the plants as top-heavy as normal. Modern hybrids are also excellent at cannibalizing nutrients out of the stalks to complete grain fill, and with smaller stalks to start with, this may also contribute to standability issues this fall. Fields with lodging problems should be targeted for early harvest.
To address combine issues for drought affected corn and soybean crops, Mark Hanna, ISU Extension Ag Engineer wrote a recent article found at the ICM News at: http://www.extension.iastate.edu/CropNews/2012/0808hanna.htm
Spider mite populations seemed to have crashed in much of the area with the recent rains and cooler temperatures. It is questionable whether there is a benefit to spraying an insecticide after beans reach R5.5 (beans half their full size). Most insecticides labeled for spider mites have pre-harvest intervals of 28-30 days, so we are getting close to the end of when insecticides can still be sprayed.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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