Preparing for Spring Scouting

Spring is hopefully around the corner and with spring comes the first opportunity to scout for a few diseases on winter wheat that only show symptoms during the cool temperatures of early spring.

First is Wheat Soilborne Mosaic Virus (SBWMV). Look for pale-yellow areas in the field after dormancy has been broken. The disease tends to be worse in low areas of fields because the vector that spreads this virus is a soil-inhabiting, fungus-like protozoan that is favored by water and wet soil (Figure 1).  Up close, affected leaves will be discolored pale-green to yellow with ‘normal’ green dashes (Figure 2). Confusingly, there is a second virus transmitted by the same soil protozoan, Wheat Spindle Streak Mosaic Virus (WSSMV). Because both viruses have the same vector they occur in the same area of the field plant and can often be found in the same plants. Furthermore, symptoms of WSSMV are similar to SBWMV. Up close the affected leaves have long discolored stripes or streaks of pale yellow and green, which may give the leaves a more streaked appearance than the SBWMV infected plants—but the differences in the symptoms are difficult to detect (Figure 2). Because of the symptom similarity, it is strongly recommended to have the plants tested to identify the virus. The WSU Plant Pest Diagnostic Clinic is able to test for these and other small grain viruses in as little as 24 hours. Infected plants lose the identifiable foliar symptoms as the temperatures begin to rise so it is crucial to check fields early in the spring after dormancy has been broken.

Last year, 2017, Eyespot symptoms were observed early in the spring before jointing. To scout for Eyespot look for golden-brown football shaped discolorations (Figure 3) on the base of the stem. For more information regarding Eyespot and our mild winter, read Dr. Tim Murray’s timely topic titled “Mild Winter Wheather and Wheat – What To Expect?”. Cephalosporium Stripe symptoms are more difficult to detect early in the spring, but become more apparent at jointing when the characteristic symptom of yellow stripes on the nodes can be easily observed.

If you observe symptoms when scouting at any time of the year and are not certain what the cause is, you are encouraged to send a sample for diagnosis to the WSU Plant Pest Diagnostic Clinic for diagnosis and management recommendations. Sending a sample is easy–just follow the instructions on the WSU Plant Pest Diagnostic Clinic website.

Winter wheat field with yellow discoloration associated with lower, wetter, areas of the field.

Figure 1: Winter wheat field with yellow discoloration associated with lower, wetter areas of the field.
Photo credit: Rachel Bomberger

Winter wheat leaves infected with Wheat Soilborne Mosaic Virus showing areas of pale-discolorations, sometimes streaks, on leaves.

Figure 2. Winter wheat leaves infected with Wheat Soilborne Mosaic Virus showing areas of pale-discolorations, sometimes streaks, on leaves. Notice the variation in appearance of the leaves thus highlighting the range of symptoms that may be observed in the field and the similarities to symptoms attributed to Wheat Streak Mosaic Virus.
Photo credit: Rachel Bomberger

Figure 3. Winter wheat infected with eyespot.

Figure 3. Winter wheat infected with the eyespot pathogen, Oculimacula species. Note the golden brown diamond shaped lesion on the lower stem that is characteristic for the disease.
Photo credit: Rachel Bomberger

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