April 2017 - Page 4


Wheat Streak Mosaic Showing up In Scattered Fields

By: Jeanne Falk Jones, K-State Agronomist

You know that sinking feeling when you are driving up to a wheat field and you can see a yellowish cast to it? There may be several things causing a yellowish cast – lack of nitrogen, environmental stress or maybe a disease.

Wheat streak mosaic virus is showing up this spring in scattered fields across northwest Kansas. This is not uncommon to see in the spring, but we may be seeing it a bit earlier than normal. In addition, much of what we are now seeing was likely from infections last fall.

The wheat streak mosaic virus is moved by the wheat curl mite. The warm open fall created conditions conducive for wheat curl mite activity. The mites’ peak reproductive activity is at air temperatures from 70 to 80 degrees. With the warm temperature last fall, we likely had quite high mite populations for quite a while after wheat was drilled.

Since wheat streak mosaic is a virus, there is no cure for the disease. Fungicide applications do not help this disease because it is not a fungal infection. In addition, insecticides or miticides are not effective for controlling the mites. Part of the reason for this, is the mites cause the edge of the wheat leaf to curl up into a tiny tunnel. The wheat curl mites are only about 1/100 inch long, so that should give you an idea of the size of the wheat leaf curl. They are very protected in these tunnels and make it difficult to get insecticide in to the mites.

Many times I get questions about spraying out or killing the wheat that is infected by wheat streak mosaic. This is not a good option for a couple of reasons. First, the mites have already moved into neighboring wheat. So, infections have already taken place, even if that wheat is not yet showing symptoms of wheat streak mosaic. It is impossible to visually know if a plant has wheat streak mosaic – if it is not showing symptoms. Then, the question becomes how you know where to stop spraying in the field to get all of the infected wheat.

Second, the herbicide that would likely be used is glyphosate. It works very slowly with the cool temperatures at this time of the year for controlling wheat. Because of this, as the wheat slowly declines in health and dies, the wheat curl mites have plenty of time to move to new, healthy wheat. Therefore instead of helping slow the spread of the disease, you may have just done the opposite.

Check out the K-State Sunflower District Agronomy website at www.sunflower.ksu.edu/agronomy for pictures of wheat streak mosaic symptoms. If you have wheat that you think may have wheat streak mosaic, please let me know. For a small cost, we can send a sample into the K-State plant pathology lab to have a virus test ran on it. Finally, be sure to follow me on facebook at K-State Sunflower District Agronomy or on twitter @CropsWithJeanne to see what I am seeing in the field.