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St. Louis Post-Dispatch

Lee Enterprises

Tuesday, March 10, 2009 10:06 PM CDT
Early season disease detection: Winter wheat

By Suzanne Bissonnette

Here’s hoping the recent warmer temperatures mean spring will truly make a showing. If that’s the case, the winter wheat in our area will green up rapidly. Recent advances in disease resistance and management continue to make wheat production profitable in Illinois. Disease management decisions start with variety selection in the fall and now resume with scouting. Wheat scouting needs to start in sync with the green up.

Virus diseases are the first diseases for you to scout. Symptoms of virus diseases are usually very clear soon after the plant breaks dormancy and begins to grow actively. The most common virus symptoms you may see are leaf tip dying and leaf yellowing, reddening or purpling. Remember that symptoms such as these can be attributed to virus infection, but may also be due to winterkill, nutrient problems or varietal characteristics.

Leaf reddening or purpling or tip die back are characteristic symptoms of barley yellow dwarf virus infection. The plants that are symptomatic now were infected by virus carrying aphids in the fall. Fall infection is much more serious in terms of yield loss compared to plants infected in the spring. Growers can expect fall-infected plants to be dwarfed and have few tillers that will likely be sterile. No in season control for virus infection exists. The only management decision that can be made is whether enough healthy plants remain to produce a reasonable stand for harvest or if the field should be abandoned and planted to another crop.

Two other viruses that cause some early season concerns are soilborne wheat mosaic and wheat spindle streak. Soilborne will typically show up in patches in low areas of the field. The mosaic symptoms are usually only fleetingly present very early in the spring, so look for these beginning now. Spindle streak on the other hand typically will show up at bit later and on the edges of the field first. Symptoms of both of these viruses are mottled or mosaic leaf discoloration and some tip die back. There is resistance to both of these diseases so knowing the resistance package of the variety you are growing can help you sort out which virus it may be.

Leaf blights may be a concern if the weather turns wet. In general, fungal leaf blights will not cause significant yield loss if they are confined to the lower plant leaves. However, as the season progresses, if the flag leaf or the flag-1 leaf is infected, a producer can expect yield losses in the range of one bushel per acre for every five percent leaf tissue that is infected.

Stagnospora leaf blight from fall infections is present on the lower leaves in some fields. Look for small tan oval lesions on the lower leaves. When raindrops hit these mature lesions spores are splashed to other parts of the plant or nearby plants in the dispersing raindrop. If rainy weather continues the disease will continue to spread up the plant. Effective fungicides are available to control fungal leaf diseases and head scab. The decision to use them should be based thorough scouting, weather forecast and yield potentials.

Regularly timed scouting trips will provide a sound basis for your disease management decisions.

Suzanne Bissonnette is an integrated pest management educator for the University of Illinois Extension.

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