ISSUE 3  May 20, 2004

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

Two of the wheat fungicides, Stratego and Quilt, are combination products of the triazole fungicide propiconazole plus a strobilurin fungicide. Several questions have been received about the proportion of active ingredients in these products. The following tables provide information on lb a.i./acre for fungicides containing propiconazole, a strobilurin, or a combination of the two.

Marcia McMullen
Extension Plant Pathologist
mmcmulle@ndsuext.nodak.edu

Since soybean acreage in the state is expected to grow by approximately 500,000 acres this year, the availability of seed may be limited. With the limited seed availability, some varieties planted may have no or ineffective resistance to Phytophthora root rot. A recent Phytophthora race survey conducted by Dr. Berlin Nelson (NDSU plant pathologist) indicated that races 3 and 4 were the most prevalent in North Dakota, while races 1, 5, 8, 21, 25, 28, 41, 43, and 44 made up the rest of the Phytophthora populations surveyed. With this knowledge, the most effective resistant genes are Rps 1k and Rps 6, which would provide protection against the most common races 3 and 4. The resistant genes Rps 1a and 1c, which are available in some regional varieties, would not provide protection against both of the prevalent races 3 and 4. If susceptible varieties will be planted into fields with known Phytophthora root rot problems, a seed treatment containing the full-rate of either Apron XL or Allegiance should be used. The full rate of Apron XL is 0.64 fl oz per 100 lbs of seed. The full rate of Allegiance FL is 1.5 fl oz per 100 lbs of seed, and the full rate of Allegiance LS is 2.4 fl oz per 100 lbs of seed.

Carl Bradley
Extension Plant Pathologist
carl.bradley@ndsu.nodak.edu