Stripe rust and leaf rust: The rust diseases are some of the most important diseases in the state and annually cause more yield loss than most other diseases of wheat. The rust diseases often become established in Texas and Oklahoma before spreading north to Kansas. We can use outbreaks in these southern areas as early indicators of problems that may arise in Kansas. This year, the early reports from Texas indicate that stripe rust levels are low in most areas and Oklahoma has yet to report stripe rust in 2017. This suggests that the risk of stripe rust in Kansas is much lower than in 2015 or 2016.
Leaf rust, however, has been more of a problem in Texas, with reports of severe leaf rust in mid-canopy prior to heading. Oklahoma reported some active leaf rust earlier this season but the dry conditions in March appeared to hold the disease in check. There are no reports of leaf rust to date in Kansas for the 2017 season. We have a lot of acres planted to varieties that are susceptible to leaf rust (T158, TAM111, TAM112, WB4458). We will need to watch for signs of leaf rust as we approach flag leaf emergence in Kansas during April.
Wheat streak mosaic: This viral disease has emerged as a serious problem in parts of western Kansas again in 2017. Wheat steak mosaic causes a yellow discoloration of leaves and severe stunting in infected plants (Figure 1). The KSU diagnostic lab was receiving samples of wheat with wheat streak mosaic already in the fall, which is an early indication that this may be an above-average year for this disease. We continue to receive samples with symptoms of wheat streak mosaic this spring and reports of above-normal levels of the disease in some areas of west central Kansas.
Figure 1. Wheat with symptoms of wheat streak mosaic. Photo by Erick DeWolf, K-State Research and Extension.
Root rots: Several samples of wheat from western Kansas have also been infected with common root rot. This fungal disease causes dark-colored lesions on the sub-crown internode and other roots (Figure 2). The damaged roots often break off when plants are removed from the soil. Common root rot is present at low levels almost every year in Kansas and survives between seasons on crop residues and organic matter in the soil. In most years, the plants have enough healthy roots to compensate for those damage caused by the disease. When soil conditions are dry, however, the damage caused by common root rot can cause more problems. Under dry soil conditions, the plants are not growing as vigorously and often have poorly developed root systems. Any damage to the root system by common root rot aggravates the drought stress and is likely contributing to the decline of some wheat fields this season.
Figure 2. Wheat with symptoms of common root rot.
Erick De Wolf, Extension Plant Pathology