A common agronomic practice that will be considered in the upcoming weeks is tank mixing a fungicide with a herbicide. Here are a couple reminders when making the decision on an early season (tillering) fungicide in wheat.
Diseases Being Targeted
An early-season fungicide is geared at managing residue-borne diseases. The pathogens responsible for these diseases are able to overwinter on host residue and can start an epidemic under conducive environmental conditions in the spring. The most common residue-borne diseases for wheat include tan spot, Septoria, and Stagonospora. Often times, more than one disease can be found on a leaf and is referred to as a leaf disease complex. For more information on fungal leaf spot diseases of wheat please reference Extension Publication PP1249.
The Decision to Spray
When scouting tillering wheat fields, an early season fungicide is likely recommended if fungal leaf spots are already found on the oldest leaf tissue. Another way to assess the value of an early-season fungicide application is to assess disease risk. The greatest amount of disease risk occurs when a susceptible variety is grown in a wheat on wheat production system, with minimal tillage and favorable conditions for disease development. Favorable conditions for fungal leaf spots are cool temperatures and prolonged periods of leaf wetness including rain and dew. NDSU routinely conducts fungicide-timing studies for management of fungal leaf spots in wheat. As a quick summary of 59 replicated fungicide trials from 2008-2015, trials were categorized into the three disease risks (low, moderate and high) based on environmental conditions and production practices. Based on this data set, when compared to a non-treated control, the mean positive yield response for an early-season fungicide was 0.1%, 3% and 4% for low, moderate and high disease environments, respectively. Although a robust statistical analysis has not been conducted on this data set, the general rule of thumb is that the likelihood of a positive yield response from an early-season fungicide will increase as disease risk increases.
Fungicide Efficacy and Expectations
There are several fungicides labeled that have efficacy on all three residue-borne leaf spot diseases. For more information, please consult the 2017 Fungicide Guide or use the NCERA-184 fungicide efficacy table. Fungicides are best used in a preventative manner and will only protect available leaf tissue at time of application. Also, it is important to remember the movement of a systemic fungicide should not be compared to the movement of a systemic herbicide. Most systemic fungicides are locally systemic (moves short distance from droplet), translaminar (moves from top side of leaf to the underside), or moves upward with xylem to a leaf tip. Therefore, as the wheat crop progresses and new leaves emerge, continue to scout fields to track disease development and progression.
The above information is from the May 18, 2017 Crop and Pest Report. Written by NDSU Extension Service Plant Pathologist, Dr. Andrew Friskop.
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