Panhandle Perspectives - Aug. 31, 2016

Stripe Rust, Part 4 – Disease Management

Robert M. Harveson, Extension Plant Pathologist, Panhandle R&E Center, Scottsbluff

Author’s note:  This is the fourth article in a four-part series on stripe rust and describes management options. Other parts in the series describe history and geographic distribution; biology and life cycle; and reasons for recent severe epidemics.

The first step to successfully combating stripe rust is to modify our previously held mind sets. Prior to 2000, we did not consider stripe rust to be a serious threat so we concentrated on other problems such as wheat steak mosaic. After 2000, a paradigm shift occurred and genetic resistance for the disease became a priority for plant breeders. This practice is currently given serious consideration and incorporated into breeding programs for new tolerant varieties.

Panhandle Perspectives
Bob Harveson

Furthermore, in the past, based on wheat prices and economics, a maximum of one fungicide application was generally employed, if that. However, we are now aware of new races of the pathogen that have become better adapted to warmer temperatures, posing a greater threat to wheat production than before. Therefore the use of single applications should be reconsidered and revised to better manage this disease.

Secondly, we also need to understand that there is no one magic silver bullet that will effectively control this disease. There are many factors that must be considered, and the integration of multiple techniques will likely be the most successful and economically sound, such as combining the planting of disease-tolerant varieties with fungicide applications.  

The use of varieties with better tolerance can delay disease development or reduce severity of disease to the point that fungicides may not be necessary. Fungicides, if utilized, can be effective, but scouting and early detection are important points that also need to be considered. Timing of fungicides also requires a number of factors to be considered. The decision to apply fungicides should be based on:

1) Disease severity: It may not always be economical to apply fungicides in the absence of high levels of disease. If the pathogen is observed primarily in the lower leaves, and the potential of disease progress is reduced (weather forecast not conducive for disease, using resistant varieties), fungicides may not be needed.

2) 10-14 day weather forecast: Weather plays a significant role in disease development and can be used to estimate need of applications

3) Crop growth stage: It is most important to protect the flag leaf, as it contributes greatly to grain fill.  If disease is noticed early, additional applications may be necessary later. However, remember that certain fungicides cannot be applied after flowering. Check labels to avoid having loads rejected at the processor due to non-compliance of fungicide label application instructions.

4) Price of wheat and yield expectations: If few inputs have been made or prices of wheat are low, using generic fungicides may be the most cost-effective method of control. It may also be most advantageous to not spray at all if yields are expected to be low in certain fields, for example in dryland fields with little precipitation during the season.