Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu
Small grains are behind and the recent cool, wet weather means that you might come across early season viral diseases in some fields, specifically Wheat Soilborne Mosaic Virus and Wheat Spindle Streak Virus. These diseases are transmitted by soil borne microbes that thrive in cool, wet conditions. Infected plants typically are chlorotic and may be stunted. Often affected plants occur in low lying areas of the field or areas suffering from compaction. However, on some occasions entire fields are symptomatic. Symptoms of spindle streak include necrotic dashes that run along the venation, giving the appearance of a spindle (Figure 1). Additional symptoms of soilborne mosaic virus are less conspicuous, but include mottling of lower foliage (Figure 2). Symptoms cease once temperatures are above 65°F and may be reduced after fertilization. Confirmation can only be made through specialized testing methods such as ELISA and PCR.
What should you keep in mind? 1) Keep track of fields with these viruses. Once the viruses are established they will be present in those fields from here on out. 2) Try to harvest or work in these fields last to prevent spread to other fields. 3) Avoid compaction. 4) Plant tolerant varieties in fields with a history of these viruses. Unfortunately many varieties are screened for these viruses as a complex, so it may be difficult to determine if you are planting a spindle streak or soilborne mosaic tolerant variety in these cases.
Figure 1. Characteristic lesions caused by wheat spindle streak virus.
Figure 2. A nursery screening wheat varieties for tolerance to soilborne mosaic virus.
Figure 3. A comparison of foliar symptoms of spindle streak (left) and soilborne mosaic (right) virus. Wheat spindle streak mosaic symptoms are typically more elongate and spindle shaped, and often contain a dark green island in the middle of chlorotic lesions.