There have been many reports this year of glume blotch on wheat, from southeast Kansas through north central Kansas. Glume blotch can be caused by the same fungus that causes Stagonospora nodorum blotch or the fungus that causes speckled leaf blotch. Initial symptoms of glume blotch are small brown spots on the glumes or awns. These expand to dark blotches, darkening the head. As lesions age, they may become tan and contain very small caramel-colored round fungal structures (visible with magnification).
Figure 1. Glume blotch in wheat. Photo by Jim Shroyer, K-State Research and Extension.
The septoria leaf and glume blotch pathogen survives within infested straw, seed, and on volunteer wheat. Infections on these sources serve as the source of inoculum to start off the disease cycle in the new crop of wheat. The disease is favored by splashing rain, high humidity, and temperatures between 68 and 82 degrees F. Where those conditions have occurred over the past month, glume blotch is now being found.
The disease characteristically moves upward from infection initiated on the low leaves within the crop canopy. If weather remains favorable, the disease will often spread to the heads. Foliar fungicides will protect wheat against glume blotch, but must be applied shortly after head emergence. Current fungicide labeling prevents application beginning at flowering or within 30 days of harvest. There are varietal differences in susceptibility to glume blotch; however, high levels of resistance are rare.
Glume blotch can result in yield losses between 10 and 20 percent. The greatest losses occur when the disease damages both the leaves and the heads. The grain produced in heads damaged by glume blotch is often small and shriveled.
Figure 2. Kernels on the left are from wheat infected with glume blotch. The kernels on the right are from normal, healthy wheat. Photo by Doug Shoup, K-State Research and Extension.
The fungus that causes glume blotch can survive in wheat residues. Fields with severe disease this year should not be planted to wheat this fall. The fungus can also survive in grain that is saved for seed. These seed infections can reduce the effectiveness of crop rotations and allow the disease to get established early in the growing season. Growers wanting to save seed from affected fields should have grain cleaned to remove the small heavily infected seeds, and use a fungicide seed treatment such as Vibrance Extreme or Gaucho XT.
Erick DeWolf, Extension Plant Pathology