Fungal diseases, including leaf rust, powdery mildew, and leaf and glume blotches, can significantly reduce winter wheat yields. Losses are greatest when disease develops on the two upper leaves during flag (top) leaf emergence in late May through kernel dough stages in late June.

Leaf rust spores are borne on air currents from southern regions and deposited by rainfall in June to July. The earlier spores arrive, the greater the potential for secondary cycles of spore production and yield loss.

Powdery mildew spores are generally present in the atmosphere above wheat fields. Infection of leaves can result in yield loss to susceptible varieties when cool humid conditions persist into June. Warm temperatures retard mildew development.

Fungal leaf and glume blotches, especially Stagonospora nodorum blotch (Figure 1), cause small to moderate yield losses almost every year. Most New York-adapted varieties are susceptible. Leaf blotches begin almost invisibly as small leaf spots in the lower canopy in fall and early spring. Splashing rain in spring and early summer moves spores to the upper canopy where they induce blighting of flag leaves and glumes. Additional spores may also arrive on air currents.

When 24 or more hours of leaf wetness coincide with the onset of wheat flowering, Fusarium head blight can cause significant yield losses and contamination of grain with more than 2 parts per million of the mycotoxin deoxynivalenol (DON or vomitoxin). Flour mills usually reject that grain. Fusarium infection during grain maturation has much less effect on yield, yet it can also result in significant DON contamination.

Foliar fungicides, 2008
Considering high grain prices, consider protecting your wheat yield and quality with a well-timed application(s) of foliar fungicide. Table 1 compares the relative efficacy of fungicides available in New York this spring. Some products, such as Folicur, Proline and Stratego, labeled in other states or Canadian provinces aren’t currently registered here.

The estimated average cost of fungicide, plus application, is about $25 per acre, though costs vary widely. There’s interest in an early spring fungicide application co-applied with nitrogen fertilizer and/or herbicide. But there’s no consistent evidence of economic return from early spring fungicides except where wheat follows wheat.

An application of fungicide, such as strobilurin, triazole or mixture, between flag leaf emergence and heading is optimal for protecting flag leaves from disease. Application of stobilurin fungicide after heads have emerged isn’t recommended because of its association with increased levels of DON. An application of Tilt (propiconazole) at the onset of flowering best suppresses Fusarium head blight and reduces DON contamination by about 25%, on average. (Figure 2) More efficacious products will likely be registered in New York in the future.

Pay particular attention to days-to-harvest restrictions on late-applied fungicide products.
Foliar fungicides have no effect on viral diseases such as wheat spindle streak mosaic or barley yellow dwarf.
It is the responsibility of the applicator to read and follow all product label directions.

More info…
Access New York advisories on the general risk of severe Fusarium head blight based on local weather and the date of onset of flowering in your wheat field at the Penn State Fusarium Head Blight Assessment Tool website: www.wheatscab.psu.edu/riskTool.html Choose the winter wheat model and click on the map of New York State.

Gary Bergstrom is a professor in the Department of Plant Pathology and Plant-Microbe Biology at Cornell University.
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