Wheat growth stages vary widely across the state, and intermittent rains and warmer temperatures may influence foliar disease development over the next week. Currently, disease levels have been low, but there are a few diseases to keep in mind when scouting wheat.
Stripe rust of wheat has now been reported in several counties in southern Indiana. The disease is generally at low incidence and severity in fields. The fungus that causes stripe rust (Puccinia striformis) produces a yellowish or orange spore, and pustules appear in a row on infected leaves, giving it a “striped” appearance (Figure 1).
Purdue Extension Bulletin BP-79-W, “Identifying Rust Diseases of Wheat and Barley” is available to aid in diagnosis of stripe rust, and can be found here. It is important to consider variety susceptibility to stripe rust, growth stage, and disease spread before applying a fungicide for stripe rust management.
Reports of virus diseases have also been prevalent across southern and central Indiana. Virus diseases of wheat are difficult to tell apart in the field and require laboratory testing for accurate diagnosis. Infected plants typically first appear in uneven patches of yellow or light green within a field, which can be confused with nitrogen deficiency or winter injury (Figure 2).
Often, symptoms appear first in low or poorly-drained areas of the field. The cool temperatures we experienced over the last two weeks enhanced symptom development of virus diseases in infected fields. Warmer temperatures will help reduce the appearance of symptoms and plants will appear to recover.
Several wheat viruses may cause these symptoms, and Purdue Extension Bulletin BP-146 describes the symptoms and management of each of the wheat virus diseases in detail.
The Purdue Plant and Pest Diagnostic Laboratory provides testing for the presence of wheat spindle streak (or yellow) mosaic virus (WSSMV), soil-borne wheat mosaic virus (SBWMV), and 5 strains of Barley yellow dwarf virus (BYDV) with a multiplex PCR detection assay. Contact the PPDL for testing fees. For an accurate diagnosis it is important to dig and submit entire plants exhibiting symptoms.
Although no control methods are available to reduce symptoms in currently infected plants, it is still important to get an accurate diagnosis for management of future wheat plantings. The best way to manage virus diseases is to plant resistant varieties in areas with a previous history of the diseases.
Producers in southern IN should start thinking about monitoring the Fusarium head blight risk map over the coming weeks in anticipation of wheat head emergence and flowering.