By Connie Strunk
Conditions have been favorable for disease development in South Dakota winter wheat fields, especially for Septoria. It’s important to scout each field to determine what diseases are on plants and what level of disease you are observing before deciding to apply a fungicide early in the season.
Septoria
Be on the lookout for Septoria, caused by the fungal pathogen, Zymoseptoria tritici this spring. Cool, wet weather favors the development of Septoria. Elliptical, tan-brown lesions with a yellow halo develop on the leaves. The centers of the lesion die, and pycnidia (sphere or ball-shaped, gelatinous and gray-brown) are visible on the lesion centers, giving the lesion a speckled appearance.
Tan Spot
Tan spot is caused by a fungal pathogen, Pyrenophora tritici repentis, which survives on wheat stubble. Tan spot can lead to poor tillering and, if left to continue developing, a reduction in yield. Tan spot lesions appear first on the lower leaves and over time can be found in the mid canopy or throughout the canopy. Tan spot lesions are dark brown surrounded by a yellow halo. These lesions often grow together (coalesce), leading to premature dying of infected leaves.
Disease Forecasting Tool
For fields planted into wheat stubble and with lower leaves showing fungal leaf spots developing, a fungicide applied at herbicide timing may be beneficial. Use the SDSU Small Grains Disease Prediction Tool to keep track of weather conditions suitable for leaf spot diseases and Fusarium head blight (abbreviated as FHB, scab). Select the growth stage and the weather station nearest your area for the forecast. This tool can predict the development of leaf spots and leaf rust based on weather conditions. The prediction tool can aid producers in making the decision to apply fungicides or not to apply fungicides. FHB prediction starts when wheat is heading.
Fungicide Selection
If the decision to apply a fungicide is made, consult the latest South Dakota Pest Management Guide - Wheat for fungicide selection.
Source : sdstate.edu