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ISSUE 15  August 13, 1998

 

CANOLA DISEASE SURVEY

    The first part of the canola disease survey was completed last week with the help of crop surveyor Carrie Buttke. Surveys were conducted in Stuttsman, Wells and Benson Counties, with 10, 10 and 7 fields examined, respectively . Each field was examined when the crop was in the swath. Eight random stops were made in each field and 5 stems examined per stop for blackleg and Sclerotinia. Ten pods were examined for black spot at every second stop. Thus, 40 stems and 40 pods were rated. Percent incidence (percent of stems infected) was recorded for blackleg and Sclerotinia. Percent severity (percent of pod affected) was recorded for black spot. Results are shown below.

County

Blackleg Incidence

Sclerotinia Incidence

Black Spot Severity

Benson

0.3%

14.0%

0.1%

Stuttsman

3.0%

11.8%

0.5%

Wells

0.3%

7.9%

0.3%

    Not all of the crop in Benson County had been cut, so another visit may be required later. The blackleg incidence in Stuttsman County was due to a field with 28% blackleg. However, the blackleg lesions appeared to be superficial, and not girdling. The lesions were not causing premature death of the plant, and so it appears that this was the low virulence strain of blackleg, wich is not serious.

    Surveys of Bottineau, Rolette, Towner, Ramsey, and Cavalier Counties will be conducted within the next several weeks.

 

CANOLA FUNGICIDE TRIALS

Large fungicide trials on canola were conducted by Kent McKay at Newburg in Bottineau County and by Bryan Hanson at the Langdon Research Center. Two smaller trials were conducted, one at Langdon by myself and one at Bisbee by Scott Halley. Two of these trials have been rated for disease. Based on raw data, it appears that both Benlate and Quadris have resulted in a reduction of Sclerotinia. The effect of rate and timing of Quadris will not be known until the data has been examined in detail. All but one of the trials will be harvested for yield.

Art Lamey
Extension Plant Pathologist

 

USE OF FUNGICIDE TREATED GRAIN CROPS FOR BEDDING OR FEED

    Several questions have been asked about using straw from fungicide treated wheat or barley for bedding or feed. Both the Tilt and the Folicur label specifically allow these uses. The Tilt label states that "after harvest, the straw from these crops may be used for bedding or feed". The Folicur label states that "straw cut after harvest may be fed or used for bedding". The labels for Benlate and all of the mancozeb products do not say anything about using straw for either feed or bedding, but they do have a prohibition against allowing livestock to graze in treated fields prior to harvest. The Tilt label also prohibits livestock grazing or cutting the green crop for hay or silage.

 

USE OF "RUSTY" CROPS FOR STRAW OR FEED

    Wheat, barley, or oat crops that have had a lot of rust infections this year may be cut for silage or feed or straw without risk to livestock from the rust spores (see information above if crop was treated with a fungicide). The leaf rust and stem rust fungi do not produce any mycotoxins that would be harmful to livestock, but overall food quality of the straw could be lessened because of the rust infections. An over abundance of rust spores could cause some allergenic effects in animals breathing the spores, but this generally should not pose a large problem. However, horses generally are more sensitive than other animals to rust spores or other molds.

 

MOLDS AND COMBINE DUST

    A number of questions have come in about black molds on grain crops at harvest. A crop consultant sent me a vial of spores taken off the dusty, black front of a combine harvesting wheat. This dust was loaded with spores of Alternaria, a fungus that is most commonly associated with saprophytic or secondary colonization of dead or dying tissue. This fungus may have developed on either prematurely ripened plants which had other problems that hastened maturity, such as root rot, scab, drown-out, etc., or the fungus colonized the mature crop after a recent rain. Alternaria is a common fungus associated with sooty molds on grains.

    The second most abundant spore type in the dust off the combine was that of Helminthosporium sativum (Cochliobolus sativus), the cause of spot blotch and black point in wheat and barley. This fungus has been noted as causing some leaf spotting on wheat and barley this year, and was very abundant in the sample. Like the Alternaria spores, these spores are big and black too, and are contributing to the black dust on the combine.

    Two other spore types found in the grain dust sample, but much less frequently, were the spores of the tan spot fungus (Pyrenophora tritici-repentis) and a few, scattered spores of the scab fungus (Fusarium graminearum). None of these spore types found were a surprise. What was surprising was that this particular sample showed only a few spores of the leaf rust fungus, Puccinia recondita.

    Dr. Len Francl, NDSU Plant Pathology Dept., launched a spore collecting balloon with a Rotorod spore sampler, both upwind and downwind from a combine harvesting a wheat field of ‘2375’ in Cass county. The height of the sampler was 30 meters. On the downwind side, in a hour sample he collected approximately 635 spores/cubic meter of Cochliobolus sativus, the spot blotch fungus, and 1441 spores/cubic meter of Puccinia recondita, the leaf rust fungus. In the upwind sample he collected 28 spores/cubic meter of Cochliobolus sativus, and 16 spores/cubic meter of Puccinia recondita. In each sample he collected only one spore of the tan spot fungus, Pyrenophora tritici-repentis, and no spores of the scab fungus, Fusarium graminearum. Francl estimates these spore numbers would translate into billions of fungal spores per combine hour. No wonder so many of us suffer from allergies this time of year.

Marcia McMullen
Extension Plant Pathologist

 

PLANT DIAGNOSTIC LAB REPORT

    There have been several samples and calls into the lab regarding a malformed head on sunflowers. The initial assertion was that Assert had caused the damage. This is not the case. The cause of this malformation is a deficiency of boron. This is not a common deficiency problem, but sunflowers are sensitive to boron deficiency. Samples are coming in from all over the state, with an estimation from a county agent that 1 out of every 3 or 4 fields was showing symptomatic heads.

    The plants submitted to the lab show signs of growth of ray florets or bracts from the head. In a couple of instances, the head was split and there were two on one stem. This may result in severe yield loss if there is a poor seed set or no seed set. This head deformity has been closely related to a concentration of boron in the upper leaves.

    Foliar sprays of boron with 0.4 to 0.5 kg B/ha at the beginning of flowering and during the main period of flowering have been recommended to manage this deficiency. There is some work toward breeding for resistance to boron deficiency and one study found that infection with vesicular arbuscular mycorrhyzae increased the uptake of boron in a boron deficient soil.

Cheryl Ruby
Plant Diagnostician


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