Posted 25 April 2012. PMN Crop News.
K-State Scientist on Wheat Rust Diseases: Correctly Identifying if Fungicides Needed – or Not – is Important
Source: Kansas State University Press Release. www.ag.ksu.edu
Manhattan, Kansas (April 19, 2012)--The wheat crop in Kansas is generally considered to be ahead of schedule thanks to warmer than normal temperatures in March. The return of cooler weather in early April slowed the crop’s development and has also favored the development of diseases, with many reports of stripe rust, leaf rust, Septoria tritici blotch and tan spot from central and eastern Kansas.
The elevated disease activity has many farmers thinking about possibly using a fungicide to help protect the crop.
“Producers have a lot of excellent fungicide options,” said Kansas State University plant pathologist, Erick De Wolf. “In my experience, based on all the data I have seen in research trials in Kansas and other states, the importance of correctly identifying situations where fungicides are needed or not needed is far greater than the choice of fungicide product.”
Most reports indicate that low levels of rust diseases can be found on the top three leaves but is probably most common on the second and third leaf down into the canopy, said De Wolf, who is a wheat disease specialist with K-State Research and Extension. Infection of the flag leaf by stripe rust has been reported in southeast and south central regions this past week. Recent reports indicate the disease is increasing rapidly in central and north central regions of the state. Tan spot and Septoria tritici blotch are at moderate levels in many fields, with infections commonly occurring on the lower leaves and mid canopy.
“The excellent yield potential of many fields and emerging risk of disease has many farmers thinking about fungicide applications,” he said. “Based on the information I have to date, it appears that most areas of central Kansas are at a moderate risk for disease-related yield loss this year. I suggest that farmers scout their fields for disease and carefully evaluate the need for fungicides.”
The residual life of a fungicide is influenced by many factors, including the rate at which the product is applied, the targeted disease and the level of disease pressure, De Wolf said. Fungicides applied at the full-labeled rate will generally have longer residual life. Fungicides will generally provide longer residual life against rust diseases (often more than 21 days) than leaf spot diseases. Some products may provide additional residual life but this extra residual does not always translate into more grain yield.
“The research I have reviewed indicates that fungicides listed in the publication Foliar Fungicide Efficacy Ratings for Wheat Disease Management 2012, EP130, will generally provide 21 days of solid protection against fungal diseases,” he said. “This includes products with the active ingredient tebuconazole that is listed in the table as the product Folicur, but is also marketed in generic formulations. These products are generally the least cost product option."
Based on questions he’s received so far in April, De Wolf believes there is confusion about the preventative and curative activity various fungicides.
“All of the fungicides listed in the Foliar Fungicide Efficacy Ratings for Wheat Disease Management publication are best applied when the disease is at low levels,” the plant pathologist said. “The triazole fungicides are generally considered to provide some limited curative activity, which means they can stop the development of fungi already inside the plant. The triazole-only fungicides include products such as Prosaro, Carmaba, Tilt and Folicur. Triazole fungicides are also included in mixed mode-of-action products such as Quilt Xcel, Stratego YLD, and TwinLine. Both the triazole and the mixed mode-of-action fungicides provide excellent protection against new infections that is often considered ‘preventive’ activity.”
It would be an error to think that a triazole fungicide does not provide preventive activity simply because it also has curative activity, De Wolf added. The curative activity is good thing, especially with a disease such as stripe rust where the fungus grows within the plant to cause additional expansion of the stripes.