Wheat Diseases Continue to Cause Problems

May 12, 2000
The repertoire of diseases on the wheat crop continues to expand this season. Fields symptomatic of wheat streak mosaic virus (WSMV) infection continue to be reported. Bob Frank of the Illinois Wheat Growers Association called in to report on a scouting trip of the wheat crop in several counties. From scouting 10 fields in Jackson County recently, Bob reported three with severe disease problems, one characteristic of WSMV, one with significant take-all, and one with significant barley yellow dwarf virus symptoms. From a multicounty scouting trip Bob took earlier in the week, he reported take-all in several western and southwestern counties. This was also the report from Ria Barrido of Growmark, who reported severe take-all in several fields in Randolph and Franklin counties.

The rolled-leaf symptom in fields characteristic of WSMV infection is prevalent this year. Omar Koester, Extension unit assistant in the Monroe/Randolph Unit, reports that some wheat fields in Monroe and Randolph counties actually have very light streaking on the leaves, but leaf roll is very prominent.

WSMV leafroll symptom. (Courtesy of O. Koester.)

Many producers have had to make the decision to replant or not. Discussions of the process for making this decision are in previous issues of the Bulletin this year. I urge you to be cautious, though. You may or may not have noticed that when I have written about WSMV and other virus diseases that have popped up this season, I always say "symptomatic" of WSMV infection or "characteristic" of BYDV infection. I don't do that because I like being vague. If you've had a course in virology or had disease diagnostic training, then you know why I don't actually say these fields are definitely infected with WSMV. It takes an electron microscope to actually see virus purified from infected tissue, and it takes a specialized serological test called enzyme linked immunosorbent assay (ELISA) to detect it. So even if the virus symptoms seem as obvious as the nose on your face, you still don't know for certain which virus may be infecting the crop. I am pointing this out because we do have several viral diseases that have extremely similar foliar symptoms, including WSMV, wheat spindle streak virus (WSSV), and soilborne wheat mosaic virus (SBWM). Fields infected with spindle streak or soilborne often recover fairly well. So even if the wheat curl mite is present and the field is "symptomatic" of WSMV, it may be worth the effort to have the field tested to actually know if that's the virus causing the disease. The Kentucky Pest Bulletin again has an excellent series of articles on WSMV and decision making related to the crop, and I urge you to read their articles on the subject this week at http://www.uky.edu/Agriculture/kpn/kpn_00/current.htm .

All the news is not bad for the wheat crop, though. Jerry Moss, a wheat grower in Pike County, called to discuss stand issues and said his crop is looking extremely good, disease free, and nearly all headed. It was a nice change to hear the good news. Thanks, Jerry.--Suzanne Bissonnette

Author: Suzanne Bissonnette