Reports of leaf rust and stripe rust; fungicide application timing
The wheat crop is growing rapidly throughout Kansas. The crop in the more advanced fields are approaching jointing in the northwest and are about a week away from flag leaf emergence in the south central and southeast portions of the state. The crop is generally considered to be about 3 weeks ahead of schedule with respect to normal growth and development. There are multiple reports of leaf rust and stripe rust in Texas, Oklahoma, and other surrounding states.
Disease presence and implications for growers
The Crops Extension team has been busy scouting for disease in recent weeks. We are finding active leaf rust and stripe rust in the state (Figures 1 and 2). Leaf rust was reported in west central and northwest, Kansas with most activity in counties bordering Colorado. Low levels of leaf rust were also observed in research plots in Riley County, which is located in northeast Kansas. The winter has been very mild in Kansas and it is very likely that the leaf rust has overwintered in the state. Stripe rust was reported in multiple counties this past week. Stripe rust is generally at very low levels with most activity reported in the southeast portion of the state (Figure 2).
Tan spot and powdery mildew have also been reported in some areas of the state.
Figure 1. Risk of leaf rust in Kansas March 18, 2016
Figure 2. Risk of stripe rust in Kansas March 18, 2016
What does this mean for wheat growers in Kansas?
The early reports of leaf rust and stripe rust are cause for concern. The risk of disease outbreaks and disease-related yield loss increases dramatically when the rust becomes established in the state prior to heading. Reports of increasing disease in Oklahoma and Texas suggest that, if weather conditions are right, more disease may move into the state soon.
What might growers consider doing to prepare for possible disease problems?
The most important thing growers can do at this stage is check their fields for disease. Scouting can help inform critical decisions about fungicides that will need to be made soon. Checking wheat varieties reaction to rust can help growers set priorities for scouting. Everest, Armour, TAM 112, and TAM 111 are widely planted in state. All of these varieties are susceptible to stripe rust and should be monitored carefully for symptoms of stripe rust. In western Kansas, were leaf rust has been more active, TAM 111 and TAM 112 are a top priority for scouting for disease because these varieties are susceptible to both rust diseases.
Fungicide options and considerations
Growers may also begin to gather information about fungicides options. Growers have access to many excellent product options. However, the price of these products and applications will be particularly important this year, because the value of wheat grain is lower relative to some recent years.
The timing of these applications is also very important. Research has demonstrated that a single fungicide application applied between boot and flowering stages of development results in the maximum yield benefit.
Fungicide applications made prior to jointing, followed by second application may also be an option. In K-State tests, these two application programs rarely result in much additional yield. It is the second application, between boot and flowering, that does the heavy lifting in terms of yield response. Also keep in mind that label restrictions often specify the total amount of active ingredient that can be applied to a crop. Using a low-cost option early could limit the product options later in the season when a second application is needed to protect the upper leaves.
One final note of caution. Keep an eye on the forecast. It may be unwise to apply a fungicide when there is a significant risk of a freeze event or other hazard on the horizon that can limit the crop’s yield potential. It is a good idea to be checking for disease and making other preparations for a potential fungicide application if conditions are right. It will be important to gather information and make a good decision in what looks like a challenging wheat production year.
Erick De Wolf, Extension Plant Pathology
Romulo Lollato, Wheat and Forages Specialist