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ISSUE 10  July 6, 2000



    Central and Southcentral regions: Jerry Schneider observed wheat leaf rust in 87% of the spring wheat fields surveyed last week in this region. Most fields had low to moderate percentages of tillers infected. The highest incidence of leaf rust (78% of tillers) was seen in a spring wheat field in Emmons county. Tan spot was the most common disease observed in all counties in these regions, with a few spots showing on flag leaves now. Septoria infections, with the small fruiting bodies evident,
were observed in 20% of the field surveyed in the region the past week. Loose smut was evident in 2-8% of wheat heads in some fields.

    Southeast and East Central regions: Matthew Gregoire found increased levels of wheat leaf rust and Septoria from the previous week, and increased numbers of grain aphids in some headed wheat. He identified English grain aphid and Bird Cherry Oat aphid on grain heads.

    Northeast region: Matthew Gregoire observed net blotch to be common on lower and mid-leaves of barley fields in Cavalier and Towner counties in the Northeast region. Wheat leaf rust was detected in several fields of spring wheat in Pembina and Walsh county, at low (2-4% incidence) levels on the bottom leaves. Tan spot was the most common wheat leaf disease observed in all counties in the eastern area of the state.

    Southwest region: Amy Dukart reported that the incidence and severity of tan spot and leaf rust on spring wheat increased throughout the southwest region in the past week. Leaf rust was observed in 60% of the wheat fields surveyed and tan spot in 100%, with some trace severities of tan spot and/or leaf rust on flag leaves now. Loose smut and wheat stem maggot are also evident as the wheat begins to head. Amy also recorded an increase in the amount of aphids (0-14% of tillers
with grain aphids) and grasshoppers (1-5/sq. yard in field margin) observed.

    North Central and Northwest Regions: Allison Marsland, Laura Neal, and Holly Semler are finding tan spot and Septoria to be the most common diseases in wheat in these areas, with severities ranging 2-20% on grain ranging from the tillering to heading stages. Bacterial leaf blight was observed in one wheat field in Ward county and loose smut was observed in a winter wheat field in McKenzie county. Grasshoppers have been averaging 1-2/sq. yard along field margins in the north central and northwest counties. Spot blotch was observed in a barley field in Mountrail county.



    With the recent rain and wind storms across much of the state, bacterial leaf streak may become evident in some fields. The causal bacterium, Xanthomonas campestris pv. translucens, survives in soil, grassy weeds, and volunteer, and are spread by splashed water. Penetration of the wheat leaf and glumes generally occurs through stomates or through wounds caused by small soil particles moving with the wind and rain storms. On leaves, the infections begin as small, watersoaked spots or streak that can enlarge and extend almost the length of the leaf blade. When dry, these lesions become brown and the leaf may look scorched. On glumes, a brown streaking is seen, generally running the length of the glume.

    John Swenson, Griggs County Agent, showed me an example of severe bacterial leaf streak on Russ wheat on June 29. Large patches of the field had plants with flag leaves that were a scorched looking brown, from the leaf tip to about 3/4 of the leaf blade. Russ wheat is a spring wheat variety that often shows symptoms of bacterial streak. Bacterial streak often shows in
patches in a field where whirlwinds occurred or wind movement of soil particles was more severe during a storm. Griggs county has seen lots of such weather recently.

Marcia McMullen
Extension Plant Pathologist



    Those who read last week’s articles on fungicides for Sclerotinia suppression in canola may have wondered about timing of these products. The timing stated on the Quadris and Ronilan labels appears to be overlapping: Quadris is to be applied at 10-25% bloom, or 3-7 days after the onset of bloom; Ronilan is to be applied at 20-50% bloom, or 4-8 days after the onset of bloom. Keeping in mind that temperature can affect how fast different bloom stages appear, it still would seem like there should be more than a day difference in the timing of applications of these two products.

    The Canola Production Manual (www.canola-council.org) provides the following information for Argentine canola:

    10% bloom = 10 flowers on the main stem, which may occur 2-4 days after the onset of bloom;
    20% bloom = 14-16 flowers on the main stem, which may occur 1-2 days after 10% bloom;
    30% bloom = 20+ flowers on the main stem, which may occur 1-2 days after 20% bloom.

    I have seldom seen 20 flowers on a main stem, as petals on the lowest flowers begin to drop and tiny pods (up to 1/4" long) begin to form; be sure to count any positions that are shedding petals and forming tiny pods.

    Specific comments on the timing of each product follow.

    Quadris should be applied at 10-25% bloom. This would be when there are 10 to 18 flowers on the main stem. Quadris will be most effective if applied before the first petals drop; thus, it should not be applied after 25% bloom.

    Ronilan should be applied at 20-50% bloom. The 20% bloom stage would be when there are 14-16 flowers on the main stem. Determining 50% bloom is more difficult. This is the stage of maximum color, but that is difficult to determine until after that stage has passed. At 40% bloom, there will be a few small pods at the base of the main stem. At 50% bloom, some of the lowest pods will begin to elongate, but the pods will extend less than half way up the main stem (probably 1/3 of the way up the
main stem). At 60% bloom, there will be pods extending over half way up the main stem (probably 2/3 of the way up the main stem). Refer to the color photos depicting the different bloom stages, as illustrated in the color brochure from BASF.



    Recent rains, together with row closure, have favored the development of Cercospora leaf spot. Cool night temperatures may have held Cercospora back until recently, but warm night temperatures are now favoring Cercospora development. More rain and warm nights are in the forecast, so growers should be looking for Cercospora, and preparing to make their first fungicide application, it they have not already done so. Cercospora has been confirmed in southern Minnesota, but as of the
morning of July 5, it had not been confirmed in the Red River Valley. I would expect that within a few days it will be confirmed in the Red River Valley.

    Sugar company agriculturists will probably be advising growers to make their first application of fungicide soon. Keep in mind that a timely first application is extremely important – if you once get behind with Cercospora, you will spend the rest of the season trying to catch up, and never quite succeeding.

Art Lamey
Extension Plant Pathologist


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