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And Now for Viruses in Wheat!

Author:

Albert Tenuta - Field Crop Plant Pathologist/OMAFRA Ridgetown
Creation Date: 30 May 2008
Last Reviewed: 30 May 2008

 

This spring positive virus test results have been received for soilborne mosaic virus (SBMV) and barley yellow dwarf virus (BYDV) and most likely based on present field symptoms we have observed recently in many parts of southwestern Ontario, positive results for wheat streak mosaic virus (WSMV) and wheat spindle streak mosaic virus (WSSMV) are soon to follow . A few factors appear to be contributing to the increase in "virus-like" symptoms. The first is many of these fields are early planted winter wheat fields and many have been planted into corn silage, seed corn or sweet corn ground. Many of these viruses are vectored or transmitted by insect vectors such as cereal aphids and the wheat curl mite which under these conditions could have infected the plants last fall.

You don't have to look hard this spring for a discussion surrounding the disappointing weather conditions we have experienced and I hate to disappoint so here is my rant! The cooler temperatures have been ideal for wheat viruses and their corresponding symptoms. This is especially true for wheat spindle streak and soilborne mosaic which are vectored not by a insect but a soil fungus (Polymyxa graminis). Soil conditions have been ideal (cool, moist) for the fungus and has limited wheat root activity in some fields which has favoured the fungus. If you add the warmer and wet conditions in the fall and early winter months this also favoured root infection by the fungus. Be patient, as warmer weather approaches (hands clasped!) many of these symptoms should disappear especially when it comes to wheat spindle streak mosaic virus.

Keep scouting those fields and make sure you can distinguish virus infection from foliar fungal diseases such as powdery mildew, etc since fungicides will not control viruses. The following table will help in identifying and better understanding the different wheat viruses.

 

Table 1. Common Wheat Virus Diseases in Ontario
  Barley Yellow Dwarf Wheat Streak Mosaic Soil-Borne Mosaic Spindle Streak Mosaic
When to expect first symptoms 6 to 8 weeks after growth begins in spring - yellow to reddish flag leaves 4 to 6 weeks after growth begins in spring Early spring. 1 to 2 weeks after growth begins in spring. Cold spring can extend symptoms longer Early spring. 1 to 2 weeks after spring growth begins. Cold spring can extend symptoms longer.
Typical pattern in field Random circular areas Most noticeable along edges of fields or near volunteer wheat . Diminishs as you go into the field. Often circular or oval areas, especially in wet areas or cool soils. More widespread in field than soil-borne mosaic.
Leaf symptoms Leaf tips bright yellow on upper leaves, or reddish flag leaves -- most distinct. Bright yellow leaves with streaking patterns toward tips. Most prominent on upper leaves. Curling of upper leaves. Pale yellow leaves with mosaic patterns Pale yellow leaves with mosaic patterns
Stunting Some-but hard to identify; fewer tillers Severe stunting from fall infections Some stunting but also some recovery after warm weather Mild stunting and fewer tillers

Other symptoms 		Poor roots; susceptible to winter injury Poor roots; wilting; prostrate tillers Poor roots; winter injury Poor roots; winter injury
Vectors Several aphid species Wheat curl mite Aceria tulipae Fungus --Polymyxa graminis Fungus --Polymyxa graminis
Conditions favoring infection Long warm fall Long warm fall. Early volunteer wheat from hail or other factors at harvest. Wet soil in fall. Cool temperatures in spring. Wet soil in fall. Cool temperatures in spring.
Control Resistant or tolerant varieties Destroy volunteer wheat. Delay planting to "fly free date." Soft red winter wheat varieties usually more tolerant than hard red winter wheat varieties Resistant cultivars. Late planting.

Modified from University of Missouri.

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