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ISSUE 16   August 24, 2000

 

NOW IS TIME TO CONTROL WSMV

    Wheat streak mosaic virus (WSMV) was observed in many western wheat fields this year and was severe in some cases. Symptoms were observed both in winter and spring wheats. The virus and the wheat curl mite that transmits the virus survived the winter in either winter wheat crops, overwintering volunteer winter wheat, or even in some spring wheat volunteers that surprisingly did not die during the mild winter of last year. A lot of volunteer plants arose last year following scattered hailstorms. In fields where producers did not control these volunteers, the incidence of wheat streak was high.

    The control of wheat streak mosaic for next year must begin now, with control of volunteers prior to planting winter wheat, plus general control of volunteers to prevent their harboring the virus and curl mite for next year’s spring crop. The green bridge between susceptible crops needs to be broken, and that is done with controlling the volunteers.

    Volunteers may be controlled with knock-down herbicides. Following treatment, wheat crops should not be planted into treated fields for at least two weeks, to assure complete destruction of volunteers. It is also important that winter wheat crops not be planted too early in the fall, when mites are still very active during warmer temperatures. A Sept. 15th winter wheat planting date or later is recommended for southern and southwest counties of ND. Seeding too early greatly increases the risks of severe losses due to wheat streak.

 

FUSARIUM HEAD BLIGHT (SCAB) AFFECTING MARKET PRICE

    Fusarium head blight (scab) is hurting grain quality and marketability again this year, particularly in the durum production areas of some northcentral and northwest counties. Much of this region received untimely rains and heavy dews during the flowering and early grain fill period of the crop. Market discounts are being received for harvested crops with vomitoxin levels above 2 ppm, and if scabby kernels are present, they are increasing % damage which in turn reduces market grade.

    Prices and discounts will be unstable until grain buyers determine the range of quality in the harvested crops. In the meantime, IF POSSIBLE, growers should harvest the more diseased portions of fields separately and attempt to reduce damage with appropriate combine settings and cleaning, plus store harvested grain until grain prices stabilize and hopefully go up.

 

CEREAL RUST SUMMARY

    The Cereal Disease Laboratory of the USDA, St. Paul, MN published their final Cereal Rust bulletin for 2000 on Aug. 8. Their summary for our region parallels findings from our wheat and barley disease survey and includes:

    Stem rust: Stem rust was not observed by Cereal Disease lab staff or our surveyors in spring wheat fields in ND. However, stem rust severity ratings of 10-40% were recorded on susceptible winter wheat cultivars Norstar, Seward and Windstar at Casselton, and considerable stem rust was observed in a commercial field of the winter wheat cultivar ‘2137' in ND. The Cereal Disease Lab states that "the increased severity of stem rust in 2000 on winter wheats can be attributed to the large amount of inoculum produced on susceptible winter wheat cultivars, eg. ‘2137'..... If current spring wheat cultivars were
susceptible to stem rust, a serious epidemic with substantial yield losses would have occurred." This is a heads up to us, we must continue to grow spring wheat cultivars with stem rust resistance (McNeal has an MS rating for stem rust), and if winter wheats with susceptibility are grown, they must be monitored closely for stem rust development and treated with fungicide if necessary.

    The Cereal Rust Bulletin reported less stem rust on barleys this year, which may be due to less occurrence of the QCCJ race this year.

    Wheat leaf rust: Lower levels of wheat leaf rust inoculum arrived in our area from the south this year as hot, windy weather in late May in the southern Plains made conditions less than ideal there for rust development. Leaf rust was common on winter and spring wheats in North Dakota this year, but less severe than in 1999. Average leaf rust severities on flag leaves ranged from trace to 10%. Some losses from leaf rust are expected in northern counties, especially in late planted fields and in fields that were not sprayed with fungicides.

    Barley leaf rust: Barley leaf rust levels were light in North Dakota this year and the Cereal Disease Lab reports losses due to this disease will be minimal this year in the U.S.

    Oat Crown Rust: The Cereal Disease Lab found trace to 50% crown rust severities in oat plots in eastern and central ND, but only trace amounts were found in northwestern ND. They reported that crown rust losses in the northern oat-growing area were less than the average of the past 5 years.

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

 

SCLEROTINIA INCIDENCE IN CANOLA

    Canola disease survey results are still coming in, but currently we have results from 118 fields in 11 North Dakota counties surveyed by Greg Endres, Jerry Schneider and Art Lamey. In addition, we have results from 30 fields in four Minnesota counties surveyed by Zach Fore. Sclerotinia stem rot was the most common and destructive disease, present in almost all fields examined, and with the highest average incidence (percent infected stems) of any disease in the survey. Currently available data are shown in the table below.

North Dakota

County # Fields % Sclerotinia
Benson

10

31

Cavalier

20

22

Foster

10

14

Hettinger

8

2

Pierce

10

22

Ramsey

10

33

Rolette

10

20

Sheridan

10

12

Stutsman

10

22

Towner

10

26

Wells

10

19

North Dakota Average*

22

Minnesota

County # Fields % Sclerotinia
Marshall

5

13

Pennington

12

21

Red Lake

10

13

Polk

3

13

Minnesota Average*

16

* Partial data for each state; not all fields or counties have been entered in the data base.

    Average incidence in the counties surveyed was 22% for North Dakota and 16% for Minnesota. These figures represent approximately a 15% loss in the North Dakota fields surveyed and 11% in the Minnesota fields surveyed.

    An incidence of 30% represents a loss of approximately 20%, which I would consider an economic loss. There were 34 fields in North Dakota with an incidence ranging from 30% to as high as 78%. This is 29% of the fields surveyed in the 11 counties listed in the table. In addition, there were six fields in Minnesota with an incidence ranging from 30% to 40%, or 20% of the fields surveyed in the four counties listed in the table. These figures represent a high percentage of fields with an economic loss.

    Blackleg was present in only a few fields, and incidences were low. Aster yellows was present in many fields, but incidences in most fields were not economic, or were only marginally economic; only 11% of North Dakota fields had 15% or more aster yellows and none of Minnesota fields had this high an incidence. Alternaria black spot on the pods was of minor consequence in all but a very few fields.

    Managing Sclerotinia. Although we always stress crop rotation, it is difficult to manage Sclerotinia if there is a heavy concentration of susceptible crops grown every year in an area. The Sclerotinia spores that cause infections are readily blown from field to field, and can even be wind-transported for some distance. Although leaving sclerotia on or near the soil surface may hasten their decomposition (authorities do not agree on this subject), sclerotia on or near the soil surface can produce apothecia, the tiny mushroom-like bodies that liberate the air borne spores. Burying the sclerotia by moldboard plowing will assure that these sclerotia cannot produce apothecia. In subsequent years shallow tillage (eg. chisel plowing) should be used to avoid returning the sclerotia to the soil surface.

    The percent of fields with economic losses suggests that many growers might profitably have used a fungicide in 2000. Research and on-farm data illustrating the benefits of using a fungicide as well as fungicide spray decisions will be discussed this winter.

Art Lamey
Extension Plant Pathologist
alamey@ndsuext.nodak.edu

 

PLANT DIAGNOSTIC LAB

    To date, there have been nearly 200 more samples submitted to the diagnostic lab this season over the 1999 season. This was the first full season that testing for Round Up residue on plant material has been offered. There were thirteen samples submitted, with 8 being positive for the presence of glyphosate, and one test result still pending. This is the only chemical we are able to actually test for at this point, in this lab.

    In general, the numbers of cultures we did for dutch elm disease on elms was about the same, sugarbeet cultures for root rot were down in numbers, but the number of samples positive for Aphanomyces was much fewer. The predominant root rot pathogen on sugarbeets was Rhizoctonia. The number of wheat samples with scab and common root rot was higher this year, but the number of small grain samples tested for Barley Yellow Dwarf Virus (BYDV) was less than last year. The number of soybean samples tested for Phytophthora was up, but the number of soybean samples with iron chlorosis was down from last year. There were more canola samples with white mold than last year, and about the same number of samples deficient in sulfur. The number of potato samples tested for late blight on foliage has been higher than last year, and harvesting is just beginning so the amount of tuber infection has yet to be realized. If we do not get the same extended, hard rains in the few weeks as was experienced in many of the potato growing regions last labor day, we should avoid the massive amount of storage rot that was observed in 1999.

    From a homeowner perspective, the rain some parts of the state received the last week or so has been much needed. It will be important to continue to water lawns and trees, especially newly planted trees, if rainfall is not any more extensive, into the fall. This is the time of year that some general leaf spot diseases may show up on trees. Most of these are not serious enough to warrant treatment. Trees will begin to go into a dormant stage in the next few weeks as night time temperatures dip down. Even some premature leaf drop is not usually serious. Lawns can be cut a little shorter again now, as temperatures are not as high as they were earlier in the summer. Do continue to cut the grass regularly into the fall so that the grass is not long over the winter months, to reduce disease potential. Fall applications of a slow release nitrogen fertilizer should be done in a month or so, late September to mid October. Gardens are starting to senesce or die out, but many vegetables may still be producing. Be sure to clean up and get rid of all plant debris as green plant material withers. This will minimize disease carryover into the next season. Do call your local county extension agent or contact the lab if you have questions about tree, grass, or garden diseases and maintenance.

Cheryl Ruby
Plant Diagnostician
diaglab@ndsuext.nodak.edu


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