Wheat Disease Update: Stripe Rust Confirmed in Nebraska; Wheat Streak Mosaic Found April 21, 2017
On April 18 wheat samples submitted to the Panhandle Research and Extension Center in Scottsbluff were positive for stripe rust. This is the first report of stripe rust (Figure 1) in Nebraska this growing season. The samples were from Sheridan County and stripe rust pustules were observed on the lower leaves, indicating that the pathogen overwintered from fall infections last year.
The wheat crop in the Panhandle region of Nebraska is still in the jointing stage and is mostly free of fungal diseases. Therefore, the recommendation at this time is not to spray fungicide but to intensify scouting efforts to determine if stripe rust is present in the field. The best timing for applying a fungicide spray is at 50% to 100% flag leaf emergence to protect the flag leaf. A pre-flag leaf spray should be considered only if stripe rust is widespread in the field and is starting to develop and spread within the crop canopy.
A survey of wheat fields on April 13 and 14 in the southern Panhandle and in southwest and south-central Nebraska revealed very little disease (Figure 2), mostly trace levels of fungal leaf spots in the lower canopy in the majority of fields. The exception was an area in Garden County with several fields that showed symptoms of wheat streak mosaic (Figures 3 and 4), a virus disease transmitted by wheat curl mites. These fields are in an area where pre-harvest hail last summer resulted in volunteer wheat that was not controlled.
Wheat streak mosaic cannot be controlled once infection has occurred. To reduce its risk in next year’s wheat crop, control volunteer wheat well before planting this fall. A few resistant wheat varieties are commercially available. If any of these varieties are available and adapted to your area, consider planting them to reduce losses caused by wheat streak mosaic.