Insects or diseases could be causing the white heads that are showing up in wheat, says Larry Osborne, SDSU research associate for small grains.
Wheat stem maggots sometimes feed on the stem several inches below the maturing head, leading to an easily detached head and stem with characteristic brown discoloration, he says.
Other insects that may cause white heads to appear include Hessian fly and wheat stem sawfly.
Wheat scab and root rots may also cause whole heads to bleach out. The SDSU Plant Diagnostic Clinic has had a number of samples submitted recently showing symptoms of these diseases.
"Root rots are normally more of a central and western South Dakota disease concern, but this year samples from as far east as the Brookings area are showing the symptoms," says Brad Ruden, interim manager said the clinic.
Although the causes leading to white heads in the field are varied, they all result in an unproductive head with little or no seed. In the case of root rot diseases, water and nutrient uptake is reduced because of damaged roots or blocked vascular tissues of the stem. Hessian fly larvae feed within the stem, and often create wounds near the base of the plant. The feeding behavior is damaging and the wounds often become infected with root and crown rotting pathogens.
These diseases often are a result of slowed seed germination and poor early growth of the plant due to dryness, freeze injury, poor fertility, compacted soils, poor quality seed, or other factors. The pathogens generally infect plants as the seed is germinating or as the seedling develops. If they survive, plants often appear normal until late in the season when heat and dry conditions increase the demand on the vascular system.
Diagnostic questions and samples can be directed to Brad Ruden at the SDSU Plant Diagnostic Clinic, SPSB 153, Box 2108, Jackrabbit Drive, South Dakota State University, Brookings, SD 57007-1090. The telephone number at the clinic is (605) 688-5545.