ProCrop

Fungicides for Early Season Use in Small Grain

Recent rains may activate fungi that cause early season leaf spot diseases in small grains. The most common early season leaf disease is tan spot of wheat.

A number of fungicides are now available for control of early season leaf spot diseases in wheat. Several are also registered for barley, if early net blotch or spot blotch should occur. The following table indicates products available, use rate, and if registered for barley, too.

All of the products have good activity against leaf spot diseases at the 4-5 leaf stage. The mancozebs are protectants and generally are less rain fast than the other products.

The fungicides are often applied in combination with herbicides applied to the crop at these early leaf stages. Some combinations of products may cause slight injury, so herbicide and fungicide labels should be checked before tank mixing. A spreader/sticker addition is not needed for the fungicide, if applied in combination with a herbicide. Also, most manufacturers of the above products have a later season use rate that is generally twice the early season fungicide use rate.

Economics of use: Early season fungicide use rates generally cost approximately $5.00/acre or less. In 2003, tests with early season fungicides on wheat resulted in a range of yield responses from 1.9 to 7.1 bu/acre and a leaf spot severity reduction from 15 to 78%, in trials with various products at Carrington and Fargo. Even the lowest yield response in 2003 would have been economic with current wheat prices.

The greatest response from early season fungicide use is seen under the following conditions:

• wet weather occurs while wheat in 2-5 leaf stage
• the wheat cultivar is susceptible to leaf disease
• wheat is planted into fields that previously grew wheat and some residue is present

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