Stripe rust on wheat was unheard of in Nebraska before the year 2000. Since then, it has become a major problem, and a good reason to really watch those fields as they green up and take off this spring.
Plant Pathologist Anthony Adesemoye said the region had wheat stripe rust epidemics in 2005, 2010, 2012, 2015, 2016 and 2017. Adesemoye works for University of Nebraska-Lincoln Extension in North Platte.
Adesemoye said producers should scout their fields regularly, starting in April, looking for orange to yellow rust pustules on the leaves. Chlorotic patches (yellowish mottling appearance) may develop on leaves before rust pustules appear. He said it is very important to protect the flag leaf. The flag leaf is the last to emerge and is critical to proper grain fill.
Adesemoye said that, for a disease to develop, three things must be present: the host, the agent and the environment. In this case, those three things are susceptible wheat plants, stripe rust fungi and cool, wet weather, he said.
If fall and winter temperatures are mild, the fungal spores can overwinter in Nebraska, Adesemoye said. That is a good reason to destroy volunteer that can form a bridge between summer wheat harvest and the time the new crop is planted in the fall, he said.
Typically, though, the fungal spores are carried by wind from as far away as Texas, in the spring, Adesemoye said.
Once the spores have landed, all they need to infect the plant is a leaf that stays moist for 8 hours and temperatures between 45 and 54 degrees Fahrenheit. Then, if cool temperatures persist, the disease can develop rapidly, Adesemoye said.
In 7 to 10 days, new fruiting bodies have formed. They can be carried by wind or splashing water, to cause new infections, and there may be four or more cycles in the same field. Disease levels in a field may change quickly within a two-week period, Adesemoye said. Final grain yield reductions of up to 40 percent, or even more, can occur, he said.
Adesemoye shared the following University of Nebraska recommendations for managing stripe rust and the other wheat rust diseases (leaf rust and stem rust):
» Destroy volunteer wheat after wheat harvest.
» Plant resistant cultivars (varieties). However, new races of the fungi can develop and may infect cultivars that previously were resistant.
» Plant cultivars with different characteristics (such as disease resistance and time of maturity) in different fields, to avoid large losses across the farm.
» Keep aware of disease development to the south of us. For example, if moderate to severe levels of rust are reported in Kansas, and wet weather is forecast, the likelihood of rust developing to damaging levels in Nebraska are high.
» Scout wheat fields regularly, starting in April.
» Apply fungicides as needed to protect the flag leaf. However, if rust develops early in the growing season, and weather conditions are good for its development, it may be necessary to apply fungicides before the flag leaf emerges.
» Read and follow all pesticide labeling carefully.