NDSU Crop and Pest Report
Plant Pathology


ISSUE 5  May 29, 2003

IPM CROP SURVEY - 2003

The NDSU IPM Survey for 2003 has begun, with field scouts examining wheat, barley, canola, sunflower, soybeans and flax for major pest problems throughout key times of the growing season. IPM scouts will be looking for pests such as grasshoppers, canola flea beetle, sunflower beetle, tan spot, Fusarium head blight, leaf rust, net blotch, soybean aphid, Pasmo on flax, plus other diseases and insects.

The IPM Scouts and their area coordinators are:

Patrick Metzger, Junior at Valley City State Univ., operating out of the Carrington Research Extension Center under the direction of Greg Endres

Tammy Link, Senior at NDSU, operating out of the Fargo Experiment Station, under the direction of Marcia McMullen and Phil Glogoza

Nicole Zahradka, Junior at NDSU, operating out of the Devils Lake Extension Office, under the direction of Terry Gregoire

Cody VanderBusch, Junior at NDSU, and Cindy Leisy, recent graduate of Dickinson State Univ., both operating out of the Dickinson Research Extension Center, under the direction of Roger Ashley.

Lorilie Atkinson, Research Specialist, and Nathan Carlson, Junior at NDSU, both operating out of the North Central Research Extension Center, under the direction of Jan Knodel

In 2002, the IPM field scouts surveyed 841 wheat fields, 272 barley fields, 324 canola fields, 192 sunflower fields, 134 soybean fields and 74 flax fields. From the information they gathered, we were able to track pest development and provide weekly updates and maps on pest distribution via this Crop and Pest Report and via the IPM webpage:

http://www.ag.ndsu.nodak.edu/aginfo/ndipm/

 

CEREAL RUST UPDATE

The Cereal Rust Bulletin #5 published by the USDA Cereal Disease Lab on May 21 indicated that wheat leaf rust was still at light levels in OK and Kansas, but that recent rains in the area may speed the increase of leaf rust.

The Kansas State Univ. Plant Disease Alert dated May 20 indicated that leaf rust was starting to build up in south central Kansas. Also, stripe rust was common and in some cases severe in fields in Kansas. Stripe rust is favored by cool, wet weather and generally is uncommon in our state. We will be looking for all rusts in our IPM survey.

It is still too early to know the potential for leaf rust in our region, but if rust would continue to increase in states to our south, the late planted grain fields will be at greatest risk.

 

ALTERNATE STAGE OF OAT CROWN RUST OBSERVED ON BUCKTHORN

Buckthorn in the Fargo area are now showing the aecial stage of oat crown rust. This overwintering stage appears as bright, light orange eruptions or aecial cups on the underside of buckthorn leaves and on twigs. On the top of the leaf is a flat orange lesion. Sexual recombination may occur in these structures on buckthorn, giving possible rise to new races of oat crown rust.

Aecial cups of Oat Crown Rust on Buckthorn
Photo courtesy of Carl Bradley, NDSU

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

 

SECTION 2(ee) LABEL FOR QUADRIS / BRAVO WEATHERSTIK TANK-MIX

A section 2(ee) label recommendation is now available for a Quadris / Bravo Weatherstik (Syngenta) tank-mix that can be applied on potatoes, tomatoes, and cucurbits. The two fungicides have different classes of chemistry, which provides for good resistance management. They will be sold as a twin-package that will contain 1 gallon of Quadris and 3.5 gallons of Bravo Weatherstik.

 

DISEASE CONCERNS WITH SUNFLOWER ON SUNFLOWER

Because planting has been delayed due to excess moisture in some parts of the state, many growers may be switching from corn, canola, etc. to sunflower. This means that sunflower may be planted back into sunflower ground. When sunflower is planted back into sunflower ground, there is a very high risk of Sclerotinia diseases, downy mildew, and Phomopsis stem canker. Sclerotinia diseases. Sclerotinia can cause three different types of diseases on sunflower: wilt, stalk rot, and head rot. Sclerotinia wilt can occur when a sunflower root comes in contact with a sclerotium (overwintering structure of the Sclerotinia fungus). Sclerotinia wilt is generally not affected by weather. Sclerotinia stalk rot and Sclerotinia head rot are caused by infections from airborne spores (ascospores) that are emitted from tiny disc-shaped mushroom structures (apothecia). Although the majority of stalk and head rot infections come from spores that are produced in the same field, spores that are produced from adjacent fields may be blown into a sunflower field and cause infections.

Downy mildew is a soilborne disease of sunflower. Under continuous sunflower, spores of the downy mildew pathogen are built up and can survive for many years in the soil. To prevent or slow-down an increase of downy mildew spores in the soil, crop rotation is very necessary.

Phomopsis stem canker is an emerging disease of sunflower in North Dakota with the potential to cause economic losses. The Phomopsis fungus survives on sunflower debris; therefore, rotation is one of the most important ways to manage this disease.

 

POTATO DISEASE FORECASTING TO BEGIN 6/2

The NDSU blightline will begin on June 2. This is the tenth year of operation of the blightline which is produced by the Plant Pathology Department and the North Dakota Agricultural Weather Network (NDAWN). The principle NDSU scientists behind the blightline are Drs. Neil Gudmestad and Gary Secor, Plant Pathology Department, and Dr. John Enz, Soils Department. The blightline is sponsored by Syngenta and the Quadris/Bravo Performance Pak, as it has been for several years. Additional Support for weather stations also comes from RDO Farms, Dow AgroSciences, and Bayer Crop Prot.

The blightline is a forecasting system for both late blight and early blight of potatoes in North Dakota and western Minnesota. It uses weather data collected from NDAWN and private weather stations to predict when conditions are favorable for these diseases. A computer program analyzes the weather data and generates values indicating whether conditions are favorable for disease and offers possible management options. The NDSU scientists review the data and provide disease severity values and make specific recommendations for disease control Monday, Wednesday and Friday of each week from the beginning of June through the middle of September. This information is available via a toll free phone # 1-888-482-7286 or the blight line website:

http://www.ndsu.nodak.edu/instruct/gudmesta/lateblight/

The data is also available in a web based format showing statewide disease severity values in a graphic presentation. The website for the statewide map is:

http://ndawn.ndsu.nodak.edu/application/potatoes.html

The purpose of the blightline is to help potato producers manage foliar diseases of potato, focusing on late blight and early blight, which can both cause serious losses if left untreated. The blight line provides management recommendations for cultural practices and fungicides applications to help control these diseases. It provides recommendations for timing, rate, interval and coverage for fungicides, and helps prevent unnecessary applications which can save producers money. The blightline also serves as an immediate form of communication for other purposes, such as insect outbreaks, other important disease reports in potato, late blight reports throughout the US, and field days. It is important for all of the potato industry to utilize this service, including growers, scouts, consultants, agrichemical industry representatives, field personnel and others. Access to the blightline is free, and is provided as a service by NDSU.

Carl Bradley
Extension Plant Pathologist
cbradley@ndsuext.nodak.edu

 

LEAF DROP ON GREEN ASH DUE TO ASH ANTHRACNOSE

byline: Prof. Bob Stack, NDSU Plant Pathology

Green ash trees are losing their leaves. The seemingly healthy leaflets just drop off the trees. Ash leaves are "compound leaves", composed of (mostly) seven to nine leaflets arranged along a stalk or "rachis." In this condition individual leaflets separate from the rachis and drop, but the leaflets appear a normal healthy green color and don't show browning or yellowing. Close examination may reveal a few tiny spots discolored brown or purple. These spots are especially noticeable on the rachis where leaflets have dropped.

Extreme leaf drop caused by Ash Anthracnose.
Picture taken in Grand Forks, ND, in June. Bob Stack Photo

This leaf drop condition is caused by a fungus disease, ash anthracnose, sometimes in combination with feeding by sucking insects. The cool, showery weather of the past several weeks favors infection by the anthracnose fungus. The cool temperatures also slow the development of the ash leaves, giving the fungus a longer time to infect. Once leaves start to fall, it is too late for any fungicide sprays to be effective because infection has already taken place.

If you see this happening to your tree, the first thing to remember is DON'T PANIC! While unsightly and worrisome, a single defoliation by anthracnose will not permanently damage the tree. When warmer weather comes, the tree will make new leaves to replace those lost. Ash anthracnose is not a new disease, it has been recognized in the midwestern states for more than 100 years. Ash anthracnose is one of many tree diseases know to occur in periodic "boom and bust" cycles -- years when it is severe followed by years when it is rare. During the early and mid 1980s, for example, anthracnose was very common in ND, especially in the Red River valley. During that time several studies were done at NDSU to better understand the disease and how it develops.

What to do about the problem. As mentioned, a single year of anthracnose, even if it causes severe leaf drop, will likely not permanently harm a tree. For the current season, rake up and destroy (burn, bury or compost) leaves to reduce the disease carryover. Prune-out cankered branches and remove twiggy growth to promote air movement within the crown. Fertilize trees in spring to promote vigorous growth.

If your tree(s) see repeated anthracnose damage in successive years, a preventive fungicide treatment may help. These need to be carefully timed to the bud break of the tree to be effective. A fungicide containing the active ingredient chlorothalonil can be used. Contact your county agent or the NDSU Plant Diagnostic Lab (701-231-7854) for current recommendations.

More information about ash anthracnose is available in the NDSU extension circular #PP697 "Deciduous Tree Diseases" available on the www at:

http://www.ext.nodak.edu/extpubs/plantsci/hortcrop/pp697_2.htm

 

ROUND UP DRIFT AND OTHER HERBICIDE INJURY CONCERNS

As the weeds and wind come up in ND, so do the claims of herbicide injury. The lab processed two Round Up drift samples this last week. We now have the capability to run two different testing methods for glyphosate, the active ingredient in Round Up. Like previous years, we can test for shikimic acid, one of the metabolites produced as glyphosate breaks down, or is metabolized, in the plant. This test is most reliable if the plant samples are tested within about 21 days of the possible misapplication; its relatively quick to run and less expensive at $125/sample. We now also have the methodology and equipment to test specifically for glyphosate itself. This test is more labor and time intensive and costs $325.

If you are concerned about Round Up drift injury, monitor the crop regularly for symptom development. To submit samples for evaluation, either for the indirect shikimic acid test or the direct method of assessing glyphosate residues, pull 15-20 plants from the affected area and do not allow them to dry out. Keep plants moist and cool, and bring them or mail them to the lab immediately after taking them from the field. Include 15-20 plants pulled from an area farthest away from the affected area, that do not appear to have been exposed to Round Up. These should also be kept moist and cool. As with any suspected herbicide injury, include name and contact information as well as field history, and a description of the pattern of symptoms both in the field and on the plant. Follow the procedures outlined in Dr. Alan Dexter’s fact sheet on documenting herbicide injury:

http://www.ext.nodak.edu/extpubs/plantsci/weeds/wc751w.htm

Call or email the lab with any questions on how to handle any suspected herbicide injury concerns.

We’ve added to our staff for the summer. Miriam Tobola will be answering the phone and providing support for the lab this summer. She started May 27 and will be with us through the summer.

Cheryl Biller
NDSU Plant Diagnostic Lab
diaglab@ndsuext.nodak.edu
701-231-7854


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