Source: Laura Sweets/University of Missouri



Wheat fields in various parts of the state are somewhat slow in greening up this spring. There are several factors which may be contributing to this problem. Wet conditions last fall in some areas delayed soybean harvest and thus delayed wheat planting. Late planted wheat may have been smaller than normal going into the winter months and may be taking longer to begin growth this spring. In many areas of the state winter conditions were not ideal for wheat, temperatures fluctuated between above normal and below normal with minimal snow cover. We have not received many complaints about stands being killed by winter conditions but have been receiving calls related to fields that are slow to green-up or that don't seem to be responding to spring fertilizer applications. Sustained warmer weather may correct some of these problems. However, this is also the time of the year when symptoms of wheat spindle streak mosaic, wheat soilborne mosaic and barley yellow dwarf may be quite evident in winter wheat fields.



So far only one sample exhibiting virus-like symptoms has been received from southwest Missouri. Symptoms on the plants in that sample were suggestive of wheat spindle streak and/or wheat soilborne mosaic. Both wheat spindle streak mosaic and wheat soilborne mosaic tend to be more severe when wet conditions occur after planting in the fall or in the late winter/early spring months. Cool spring temperatures also enhance symptom development of both wheat spindle streak mosaic and wheat soilborne mosaic. It is difficult to predict how widespread and severe wheat spindle streak and wheat soilborne might be this season. Although there are no rescue treatments for wheat virus diseases, it is still a good idea to scout fields for plants showing virus symptoms and to send in samples to identify the virus or combination of viruses that are present so that proper preventative management measures can be used the next time wheat is planted in that field.



Descriptions of the wheat virus diseases most likely to occur on winter wheat in Missouri are given in the following paragraphs.



Symptoms of wheat spindle streak mosaic appear in early spring as yellow-green streaks or dashes on the dark green background of the leaves. These lesions usually run parallel to the leaf veins and tend to be tapered at the ends giving the lesions a spindle shaped appearance.



Foliage symptoms are most obvious when air temperatures are about 50