by Jonah E. Kaya and Rachel Bomberger, WSU Plant Pest Diagnostic Clinic
Dryland cropping system samples have begun coming into the clinic. While the normal early season issues including Rhizoctonia Root Rot and abiotic leaf spots are expected we’ve also encountered: Septoria Leaf Spot and Soilborne Wheat Mosaic Virus.
Septoria Leaf Spot is a fungal disease that affects wheat and other cereals and is caused by Zymoseptoria tritici (frequently known by its anamorph, Septoria tritici). This fungus survives on infected wheat plants or wheat stubble to produces spores when temperatures rise and there is moisture. Spores move with the wind and water, such as during spring rains; disease pressure increases if there are two consecutive rainy days.
Early symptoms of this disease appear as chlorotic spots. As the disease progresses, the spots expand into oval-shaped necrotic lesions and may be encircled by a yellow halo. What makes these symptoms different from other common leaf issues, such as physiological leaf spot, is the presence of tiny black fruiting bodies.
Methods to control include rotating out of cereals to reduce the amount of inoculum in that particular field. In some cases, tilling can also help to reduce severity of the disease by burying any infected plant material. Lastly, fungicides and seed treatments can both be effective management techniques as well. More information can be found at the PNW Handbooks page for Wheat (Triticum aestivum)-Septoria tritici Blotch and American Phytopathological Society’s educational resource Septoria tritici blotch (STB) of wheat.
Next is Soilborne Wheat Mosaic Virus; as the name implies this is a virus that is survives in and is spread through the soil by the fungal-like organism Polymyxa graminis. The pattern and distribution of the infection in the field looks like other soilborne diseases with patches and low lying areas more likely to be symptomatic.
Symptomatic leaves are lighter green to yellow in color and often have ‘dashes’ of different colors typical of mosaic viruses. Infection occurs in the fall and symptoms appear in early spring. Symptoms fade and plants appear to recover as temperature increases in spring however the damage remains and yield is reduced.
Variety selection is important for this disease as common management practices are of little effect. Crop rotation is impractical as the vector survives long-term in soil. And, unlike Barley Yellow Dwarf Virus, which is transmitted by various aphid vectors, SBWMV’s vector Polymyxa graminis cannot be controlled with chemicals. More information and variety information can be found at the PNW Handbook page for Soilborne Wheat Mosaic Virus.
As with many of the plant problems we face, effective control can only happen when we have the correct diagnosis. The Plant Pest Diagnostic Clinic is here to help you with diagnosing plant problems! The clinic is open year-round and can accept all types of agriculture crop as well as ornamental and private homeowner plant samples.
For questions or more information please contact the Plant Pest Diagnostic Clinic / plant.clinic@wsu.edu.