By Scout Nelson
Wheat Streak Mosaic Virus (WSMV) is now spreading across South Dakota wheat fields, especially in winter wheat. This viral disease mainly affects grass crops and is known to lower crop yield quickly. In 2025, it is causing major problems in the Great Plains and may also affect spring wheat, which is less resistant.
The virus is spread by a tiny insect called the wheat curl mite. These mites live in leftover volunteer wheat, often left behind by hail-damaged crops. When spring and winter wheat fields overlap, the disease spreads between seasons. Mild winters, like the one in 2024–2025, allow the mites and the virus to survive and spread more easily.
WSMV symptoms start with small yellow lines or streaks on leaves. As the disease grows, yellow mosaic patterns appear, and the plant becomes stunted. Leaves turn patchy green and yellow. Tiller production drops, and the crop weakens.
There are no sprays or chemical cures for WSMV. Farmers must use cultural practices to prevent and control its spread. This includes removing volunteer wheat and other grass hosts before planting, using resistant wheat varieties, and planting at the right time in cooler weather. Farmers should also avoid planting both spring and winter wheat close together, which helps break the “green bridge” that connects the virus between seasons.
If you suspect WSMV, reach out to experts at South Dakota State University (SDSU) Extension. Questions can be directed to plant pathologists Madalyn Shires or Connie Strunk. Samples can be mailed to or dropped off at the SDSU Plant Diagnostic Clinic in Brookings, South Dakota.
Photo Credit: gettyimages-ianchrisgraham
Categories: South Dakota, Crops, Wheat, Harvesting, Rural Lifestyle