NDSU Crop and Pest Report
Plant Pathology


ISSUE 3  May 20, 2004

UPDATE ON EARLY SEASON FUNGICIDE USE IN SMALL GRAINS

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.

Product

Active ingredient

Early season use rate

Crop

Tilt, Propimax, Bumper

Propiconazole

2 fl oz

Wheat, Barley

Stratego

Propiconazole + Trifloxystrobin

5 fl oz

Wheat

Quadris

Azoxystrobin

6.2 fl oz

Wheat, Barley

Headline

Pyraclostrobin

3 fl oz

Wheat, Barley

Quilt

Propiconazole + Azoxystrobin

7 fl oz

Wheat, Barley

Penncozeb, Manzate, Dithane

Mancozeb

1-1/12 lb

Wheat, Barley

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:

 

CEREAL FUNGICIDE EQUIVALENTS

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.

Quilt: = propiconazole + azoxystrobin

Quilt
oz/acre

propiconazole lb a.i./acre

azoxystrobin lb a.i./acre

7

0.057

0.034

14

0.114

0.069

Stratego: = propiconazole + trifloxystrobin

Stratego
oz/acre

propiconazole
lb a.i./acre

trifloxystrobin
lb a.i./acre

5

0.041

0.041

10

0.082

0.082

Tilt: active ingredient = propiconazole

Tilt
oz/acre

propiconazole
lb a.i./acre

2

0.056

4

0.113

Headline: active ingredient = pyraclostrobin

Headline
oz/acre

pyraclostrobin
lb a.i./acre

3

0.049

6

0.098

Quadris: active ingredient = azoxystrobin

Quadris
oz/acre

azoxystrobin
lb a.i./acre

6.2

0.097

7.7

0.12

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

 

PHYTOPHTHORA ROOT ROT OF SOYBEAN: RESISTANT VARIETIES AND RACES

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


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