Too Early for White Wheat Heads

Mike Rankin
Crops and Soils Agent
University of Wisconsin - Extension

Why are the heads turning white in my wheat field? 

     As if there are not enough problems this year, it appears that Fusarium head scab is prevalent in many winter wheat fields this year.  Our two previous bad head scab years were 1991 and 1996.  The disease appears to be widespread throughout the Midwest and is cause for concern on several fronts.  The causative fungus may produce mycotoxins and scab infected wheat is often severely discounted or rejected when it is sold.  Ohio State University considers scab to reach “epidemic” proportions when 10 percent of the spikelets are affected within a field.  At this level, yield, test weight, and grain quality are significantly impacted.  A large amount of rainfall during wheat flowering sets up a bad head scab year.  Certainly that would qualify 2004. 

     It’s relatively easy to identify wheat scab.  Either entire heads or individual spikelets on wheat heads turn bleach white prematurely.  On closer inspection, there is generally a pink to salmon colored fungus growing at the base of the infected spikelets.  Infected spikelets often produce grain kernels that are small or shriveled.  In some situations there may be no kernel produced at all.  By harvest, we often see black secondary organisms grow on the wheat head.  This makes for a very dirty and dusty wheat harvest.  Many wheat growers will recall the cloud of black dust that emitted from combine heads during the 1996 growing season. 

What are the key mycotoxin issues?

     As mentioned previously, wheat buyers are very sensitive to scab infected wheat because of the possibility that mycotoxins may be present.  Vomitoxin (DON) and zearalenone are the two most common mycotoxins associated with head scab.  Swine and other monogastrics are the most sensitive to mycotoxins.  There is also a concern for human health.  In severe cases, farmers and grain handlers can become ill from breathing the dust and fungal spores generated from scab infected wheat. 

     Nutritionists suggest that dairy cattle can tolerate up to 5 parts per million (ppm) vomitoxin in the total ration dry matter.  Scab-infected wheat can be limit fed to replace up to 25 to 30 percent of the shelled corn in milking cow rations, or about 5 pounds of wheat per cow per day.  Less wheat can be fed where a higher percentage of the diet consists of high moisture corn or corn silage because this will result in an excess amount of rapidly fermentable starch.  Scab infected wheat should not be included in calf starter rations.  The energy value of scab infected wheat needs to be discounted.  

Is there a test for mycotoxins?

     Yes.  Several commercial and public laboratories offer mycotoxin testing.  Testing is highly recommended in situations where wheat will be fed to animals.