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ISSUE 3  May 18, 2000

WHEAT DISEASE UPDATE

    The Plant Pathologist from the Kansas Dept. of Ag. states that barley yellow dwarf continues to be found at high levels in much of the Kansas wheat crop, plus wheat streak mosaic (WSMV) symptoms are also at their zenith (although not as severe or widespread as BYDV). Leaf diseases are now found on flag leaves, and leaf rust in south central Kansas has increased significantly.

    In North Dakota, symptoms of tan spot on winter wheat have been reported (Greg Endres, Area Agronomist at Carrington). Wheat streak mosaic virus was confirmed in a winter wheat field from Dunn Co. (Observed by Roger Ashley, Area Agronomist, Dickinson, and confirmed by Plant Diagnostic Lab, NDSU). The chances are very high that this field infected with WSMV will only go backward, and yields will be very disappointing. As it is still relatively early in the spring,
the producer has the opportunity to turn this infected crop under, and then plant to a row crop like sunflower.

 

SECTION 18 FOR FOLICUR ON WHEAT AND BARLEY

    In late March, EPA granted a Section 18 Emergency Exemption for the use of Folicur fungicide on wheat and barley for the suppression of scab. The dates of this exemption are from June 15 to August 25, 2000. The use rate is for 4 fl oz, with a maximum of one application per season. It should be applied in a minimum of 10 gpa by ground sprayer or 3 gpa by aircraft sprayer. The Section 18 label states that the product may be applied up to 50% heading and application may not be made within 30 days of harvest.

 

FUNGICIDES REGISTERED FOR WHEAT FOR 2000

    Mancozebs and Tilt are the two fungicides with labels that allow early season application (prior to jointing) for tan spot control. These two products also may be applied later in the season for leaf diseases and scab control: Mancozebs (1-2 lb/acre rate; no more than 3 applications per season ), up to 26 days before harvest; Tilt (4 fl oz/acre maximum per season), a 24 C label allows heading application with a 40 day preharvest interval.

    Other fungicides also have registration for application to wheat for leaf disease and/or scab control. Quadris has full federal registration for wheat, at 6.2-10.8 fl oz/acre with a 45 day preharvest interval; Benlate is applied at 0.25-0.5 lb/acre and has a 21 day preharvest interval; Folicur has a Section 18 Emergency Exemption for use in 2000, at 4 fl oz/acre and a 30 day
preharvest interval. ManKocide (mancozeb + copper) and Copper fungicides alone are also registered for wheat. The following table has some suggested retail prices for the most commonly used products. Prices may vary slightly according to individual distributor or if packages of products are purchased.

Wheat
fungicide

Full label rate/acre

Suggested
retail price for label rate

Mancozebs

1-2 lb

$2.50-$5.00

Tilt

4 fl oz

$9.50

Quadris

6.2-10.8 fl oz

$14.53-$25.30

Benlate

0.5 lb

$8.43

Folicur

4 fl oz

$9.60

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

 

CHALKY SOYBEAN SEED

    Last week I had a telephone call about chalky soybean seed. If the seed is chalky in appearance, it is probably due to Sclerotinia. However, if the seed has a white crust on it, it could be due to downy mildew. Based on environmental conditions last summer, Sclerotinia seems more likely.

    If Sclerotinia is suspected in a seed lot, a germination test is recommended. This would answer two questions: 1) is the germination satisfactory? and 2) how much of the seed is infested or infected with Sclerotinia? If the germination test reveals many seeds with profuse white mold on them, this suggests that many seeds are infested or infected with Sclerotinia. In such a case, a healthy seed source would be preferred. Research in Illinois has shown that even low levels of infection can result
in introduction of Sclerotinia into a relatively clean field. This research also demonstrated that both Maxim (fludioxonil) and Rival (captan + PCNB + TBZ) are highly effective against seed borne Sclerotinia, although neither product is registered for Sclerotinia suppression. The label for Apron Maxx RTA (fludioxonil + mefenoxam), however, does list suppression of seed borne Sclerotinia. If infested seed must be used, one of these seed treatments would help to raise seed quality, improve
germination and minimize the introduction of Sclerotinia into the field to be planted.

 

SOME USEFUL SUGARBEET WEB SITES

American Crystal Sugar Company, Agronomy: http://www.crystalsugar.com/agronomy/index.asp.

     This site provides "white papers" on various subjects as well as agronomy papers on a range of subjects, including excellent information on Cercospora leafspot and Aphanomyces root rot. It also has a search engine for information contained on the site and links to related web sites.

Sugarbeet Research and Extension Board: http://www.sbreb.org.

    This site has a search engine that searches all of the reports published in all issues of the Sugarbeet Research and Extension Reports. All reports are available on the site. The presentations given by speakers at the winter seminars are also available. Production tips are given and the results of the coded variety trials are posted on the web site.

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

 

PLANT DIAGNOSTIC LAB

    Spruce trees are the most common sample coming into the lab right now. Spider mites are already showing on spruce as well as some other ornamentals. On spruce and other woody species, simply hosing out the tree or shrub periodically with a steady stream of water will wash the mites out and down into the soil where they will not likely cause any more damage. There are other products available to manage mites, and they include: dormant (horticultural) oils, acephate (Orthene and Isotox), diazinon, and dicofol (Kelthane).

    The diseases most commonly occurring on spruce are Rhizosphaera needlecast and Cytospora canker. Both of these diseases typically exhibit symptoms of needle browning, beginning in the lower branches. In general if the browning occurs from the inside of the tree and moving out, it is more likely to be Rhizosphaera. If the needles are browning from the tips of the branches and moving down the branch toward the center of the tree, and if there is sap oozing from branches with browning needles, the problem is more likely to be Cytospora canker. While both are caused by fungi, management is different. Rhizosphaera needlecast requires two applications of chlorothalonil in the spring, for successive years, to bring the disease under control. There are no fungicides for Cytospora canker, symptomatic branches must be pruned out for successive years to stop the spread of the disease. These respective management tools are both highly effective, but only if they are being used to treat the correct disease. The Plant Diagnostic Lab can provide assistance in determining which disease might be affecting your trees. Samples should be taken from an area of the tree showing symptoms, and if possible, include branches showing both brown and green needles. As a reminder, always apply pesticides with care and according to label instructions and specifications.

    One of the services the lab now offers is plant tissue testing for potential Roundup injury. In order for this testing to be most effective, samples must be received within two weeks of the application of Roundup. After two weeks, the plants will either die or metabolize out the chemical, and the herbicide will no longer be reliably detectable. This requires frequent and diligent scouting of crops, shelterbelts, or other plant material for injury symptoms - a good general practice for early detection of disease, insect injury, or possible nutrient problems as well.

Cheryl Ruby
Diagnostician
diaglab@ndsuext.nodak.edu


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