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Know the Conditions for Rust in Wheat

May 17, 2019
An agronomic photo showing wheat diseases.

Stripe Rust

A common question amongst growers is, “Is there going to be rust in my wheat, and am I going to need to spray?” To better determine the response to this question, we need to first learn what it takes for this disease to develop. A handy tool to use when considering infection risk is the Disease Triangle. For a fungal disease to develop you must have all 3 components of the triangle – Host, Pathogen and Environment. With recent reports of rust in OK, KS and KY wheat, now is the time to assess your risk.

Once wheat is planted, the host point of the triangle is present. Some varieties tend to be a more susceptible host than others by their natural genetic makeup.

There is a possibility of the rust pathogen overwintering further north in more moderate winters, but typically it just overwinters in TX. As weather warms, rust spores will blow in the wind, infecting plants along the way. Spores land on the leaf, and if environmental conditions are favorable, the fungus germ tube will penetrate the leaf surface, infecting the plant. As the disease progresses in its lifecycle, it will again sporulate and send more spores into the wind currents, spreading the disease throughout the area and further north.

The environment plays a big role in closing the disease triangle for rust in wheat. For stripe rust

development, the ideal conditions for infection include temperatures of 45 to 54oF with 8 hours of free moisture on the leaf, such as a heavy dew and cloudy day. The ideal temperature range for the disease to continue to develop is 50 to 59oF.

Leaf rust favors warmer temperatures than stripe rust. The optimum temperature range for leaf rust infection is 59 to 68oF, with the optimum range for development being between 68 and 71oF. Infection requires 6 hours of free moisture for leaf rust to infect plants.

The temperatures listed are ideal temperatures, but don’t mean the disease disappears when warmer weather appears, just slows in development. If all 3 corners of the triangle are present, it’s time to take charge and defend crops against potential yield loss.

Next Step: Management

To help keep your wheat disease-free, we recommend applying a fungicide at 50% flag leaf emergence when disease conditions are favorable. Your variety’s rust tolerance level and yield potential are 2 other indicators that can guide your fungicide choice.

We have several fungicide options to fit a variety of needs.

For fields with low disease pressure or where the need for long-lasting residual control is not anticipated:

  • Alto® 100 SL fungicide provides curative control of infections from the 24-72 hours before application and for a short time after application. It is a Group 3 fungicide and contains a single active ingredient.

For fields anticipating moderate disease pressure, in irrigated or dryland wheat that has a thick canopy and 40+ bu/A yield potential, or when conditions are conducive to rapid disease development:

  • Quilt Xcel® fungicide will deliver curative and preventive control with good residual. A combination of Group 3 and Group 11 active ingredients, Quilt Xcel also helps plants withstand wet conditions with stronger-deeper roots.

For fields anticipating moderate to heavy disease pressure, in irrigated or dryland wheat that has a thick canopy and 40+ bu/A yield potential, when conditions are conducive to rapid disease development, or when there is an anticipated need for extended protection from rust:

  • Trivapro® fungicide features 3 robust active ingredients that deliver the longest-lasting control and plant-health benefits. By combining active ingredients from Group 3, Group 7 and Group 11 fungicides, Trivapro can help improve water-use efficiency that slows water loss during dry conditions, speed canopy closure to deprive weeds of sunlight and enhance the plant’s ability to use the sun’s energy for greener flag leaves and fuller heads.

With the weather variability many areas are experiencing this spring, be sure your wheat fields are protected from rust so your crop can reach its yield potential.

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