Wheat in eastern Oregon is produced mostly as a 2-year rotation of winter wheat and summer fallow. Maximum agronomic yield potential is expected with early September planting dates but actual yields are generally highest for plantings made in mid-October. Field experiments with sequential planting dates from early September to December were performed over 4 years. Associations among yield, disease incidence, and 19 moisture and temperature parameters were evaluated. Incidence of Cephalosporium stripe, crown rot, eyespot, and take-all decreased as planting was delayed. Crown rot and eyespot were negatively correlated more significantly and more frequently with temperature than moisture parameters, and take-all was more associated with moisture than temperature. Rhizoctonia root rot was unrelated to planting date and climatic parameters. Crown rot was identified most frequently (4 of 5 tests) as an important contributor to yield suppression but yield was most closely associated (R2 > 0.96) with effects from a single disease in only two of five location–year tests. Yield was most related to combinations of diseases in three of five tests, complicating development of disease modules for wheat growth-simulation models.
INFLUENCE OF SEED DRESSERS’COMPOSITION ON THEIR EFFICACY AGAINST WINTER WHEAT DISEASES
