The 2000 wheat crop might be remembered as being one of the higher average yields produced in Illinois, but let's take a moment to remember several fall and spring diseases that caused concern and, in some cases, stole some bushels from the Illinois wheat crop again. This article focuses heavily on the viral diseases and what adjustments might be made to help reduce their impact on the upcoming wheat crop. It will be followed in the next issue by an article that deals with seed treatment fungicides. |
Field diagnosis of viral diseases is very difficult and should be confirmed via laboratory diagnosis. Since virus pathogens cannot be cultured in the lab like fungi or bacteria, plant disease clinics around the country often send suspected virus-infected samples to a company called Agdia, Inc., for specialized testing. Such testing is expensive, often $50 or more per sample, plus shipping. In the past, Agdia offered a reduced fee structure when samples were routed through plant diagnostic clinics, but this is no longer the case. As a result, the University of Illinois Plant Clinic recommends that growers and consultants work directly with Agdia, or similar companies, when seeking laboratory virus confirmation. Agdia's address is: Agdia, Inc., 30380 County Road 6, Elkhart, IN 46514. Call ahead for the current "wheat screen" test price and for instructions on submitting the sample (219-264-2014 or 800-622-4342). You can also access Agdia on the Internet at http://www.agdia.com/testing.
As mentioned in Table 1, barley yellow dwarf virus (BYDV) and wheat steak mosaic virus (WSMV) infections take place in the fall and again in the spring. Since it has been shown that fall infections tend to be the most damaging, you can reduce the impact of these diseases by reducing fall infections. To reduce fall infections, its important to take advantage of the fact that the virus needs the vector (e.g., aphid or mite) to get around, and neither can function without a green host or function at low temperatures. Most everyone knows this "trick" as planting after the fly-free date, which has been used for decades to evade Hessian fly infestation. Fly-free dates for each county are listed on page 39 of the 1999/2000 University of Illinois Agronomy Handbook, available through your local Extension office. Delayed planting breaks up the "green bridge," or the overlap in growing season between two host crops such as corn and winter wheat. Essentially, the virus and vector population crashes because there are virtually no live hosts left and then it gets too cold for the vector to function. Virus diseases do not disappear forever because they either overwinter in other weedy or volunteer hosts and await the appearance of its vector in the spring, or they arrive with the vector as it moves north in the spring. For further discussion about the "green bridge," refer to the article entitled "Wheat Streak Mosaic Virus in Field Corn" in the June 30, 2000, issue of this newsletter.
Recently, the Wheat Performance in Illinois Trials2000 was published by the University of Illinois (contact your Extension office for a copy). In addition to yield, test weight, and plant height data for six locations across Illinois, the report contains information about many other important agronomic and pest-related characteristics. While the report addresses varietal resistance to leaf rust and septoria leaf spot, it does not provide virus-resistance ratings. For a number of reasons, published data on varietal resistance to virus diseases are scarce in the Midwest. In most cases, you should be able to get some resistance information from your seed sales representative. Dr. Fred Kolb, University of Illinois Small Grains Breeder, recently shared the results (Table 2) from an Urbana test plot where 15 public and private varieties were screened (1999 and 2000) for resistance to WSMV and BYDV. In addition, you may find the Kansas State publication entitled Wheat Variety Disease and Insect Ratings 2000 (MF-991) useful; it lists several soft red winter wheat varieties adapted to Illinois and their reaction to a wide range of viral and fungal diseases. You can get a copy of the KSU publication by calling (785)532-5830 or via the Internet at http://www.oznet.ksu.edu/library/plant2/MF991.pdf.-- Bruce Paulsrud