ISSUE 2    May 12, 2005

POTATO LATE BLIGHT HOTLINE TO OPERATE IN 2005

The Plant Pathology Department at North Dakota State University will again be providing the potato late blight hotline service at no charge to the potato industry of North Dakota and western Minnesota in 2005. This will be the eleventh year that this service has been provided and sponsored by Syngenta Crop Protection and Amistar fungicide. The hotline uses local weather data collected from weather stations throughout our area to forecast the occurrence and spread of late blight in fourteen non-irrigated and nine irrigated production areas in ND and western MN. The data is processed by the North Dakota Agricultural Weather Network (NDAWN) and analyzed by a computer program (WISDOM) to forecast when conditions are favorable for late blight to occur.

The forecast information is used by plant pathologists Gary Secor and Neil Gudmestad to make late blight management and fungicide recommendations. The recommendations are made Monday, Wednesday and Friday of each week during the growing season. The first late blight hotline will be Wednesday June 1st, and the hotline will continue through mid September depending on disease pressure. The hotline will also be used to confirm late blight infection and serve as clearing house for national late blight information. In addition to late blight forecasting, the hotline also provides cumulative P-values for early blight disease forecasting and management recommendations. Finally, it serves to alert growers of other disease and insect news, as well as posting messages of general interest such as potato field day dates.

The hotline recommendations can be accessed by phone or website.

The toll free phone number is 888.482.7286

The NDAWN website for potato disease forecasting, produced by Dr. John Enz of the Soil Science Department at NDSU, uses colored maps of ND to pictorially illustrate the late blight severity values (both two day and seasonal), favorable day values and P-day values for early blight throughout ND. That site is:

http://www.ndawn.ndsu.nodak.edu  Go to applications and then the drop down box to potatoes.

The NDSU Plant Pathology late blight website is:

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

This website contains current foliar disease recommendations, historical records, potato disease profiles and fungicide trial results.

Growers and scouts are encouraged to send suspect late blight samples to us for positive identification.. It is important to receive samples as quickly as possible after collection. Leaf samples should be placed in a slightly inflated zip-lock plastic bag without a wet towel and sent to:

Gary Secor, Plant Pathology, Walster Hall 306, North Dakota State University, Fargo, ND 58105. Our phone number is 701.231.8362 and email address is gary.secor@ndsu.edu . We look forward to a successful potato year.

 

NDSU Plant Diagnostic Lab

Seed health testing has begun to slow down in the lab. Last-minute screening for potato viruses is winding down. Very low to no levels of PVY and PLRV were detected in commercial potato seed lots, which is good news for seed growers. Over 150 seed lots were tested for bacterial ring rot, and all lots were negative. Several lawn and spruce samples were submitted to the lab in recent weeks, including one that was diagnosed with Rhizoctonia brown patch. Spruce samples that have been submitted show symptoms of spider mite injury and/or winter injury. One spruce sample showed symptoms consistent with those associated with herbicide injury. In addition to diagnosing plant problems, the Plant Diagnostic Lab provides services in weed and other plant identification and insect identification (such as ticks). The lab also evaluates home and commercial building samples for mold contamination.

Does your lawn have brown or yellow circular patches that become visible as soon as the snow melts? Do these patches expand and worsen over time? It is possible your lawn may be infected with one or more snow mold diseases or several other types of turfgrass diseases. In the case of a sample submitted earlier this spring, a Rhizoctonia species was isolated. Several species of this fungus can cause diseases on grass, and symptoms can vary widely, depending on grass variety, fungal species, time of year, and mown height of the grass. Cultural practices that can help manage diseases caused by Rhizoctonia species and other fungi include avoiding excess nitrogen while applying sufficient levels of phosphorous and potassium, providing good drainage, reducing duration of leaf surface wetness, increasing aeration, and keeping thatch levels below one inch. Good drainage is critical to reduce humidity in the microclimate. Minimizing leaf surface wetness can be achieved by watering in late morning and afternoon (not during the evenings or early morning), or by mechanical means, such as dragging a hose or rope or pole across the lawn. Increased aeration can be accomplished by pruning overgrown shrubs and trees. Excess thatch can exacerbate disease problems, so reducing thatch to below one inch is recommended. Core aeration can help reduce thatch levels while improving drainage and aeration. However, this technique should only be performed during times of optimal grass growth, such as May and August in North Dakota. For more information on maintaining a healthy lawn, browse the NDSU Extension website, http://www.ext.nodak.edu , and click on the ‘Publications’ link, or contact the NDSU Plant Diagnostic Lab for more information.

Correction: An incorrect e-mail address for the NDSU Plant Diagnostic Lab was published in last week’s Crop and Pest Report. The correct e-mail address for the NDSU Plant Diagnostic Lab is diaglab@ndsuext.nodak.edu.

Kasia Kinzer
Plant Diagnostician
NDSU Plant Diagnostic Lab

 

RECENT RAINS MAY BRING EARLY SEASON TAN SPOT IN WHEAT

Recent rains may activate fungi that cause early season leaf spot diseases in small grains. The most common early season leaf disease is tan spot of wheat. Although cool temperatures of the week of May 9-13 will delay crop development and activity of tan spot, weekend warming may result in some early season disease development and also move crop development of early planted fields into the 4-5 leaf stage, a time when early season fungicide is often applied with early herbicide application.

A number of fungicides are available for control of early season leaf spot diseases in wheat. Several are also registered for barley, if early net blotch or spot blotch should occur. The following table indicates products available, use rate, and if registered for barley, too.

Tan spot in wheat image

 

Product

Active ingredient

Early season use rate

Crop

Tilt, Propimax, Bumper, Contend

Propiconazole

2 fl oz

Wheat, Barley

Stratego

Propiconazole + Trifloxystrobin

4-5 fl oz

Wheat

Quadris

Azoxystrobin

6.2 fl oz

Wheat, Barley

Headline

Pyraclostrobin

3 fl oz

Wheat, Barley

Quilt

Propiconazole + Azoxystrobin

7 fl oz

Wheat, Barley

Penncozeb, Manzate, Dithane

Mancozeb

1-1/12 lb

Wheat,Barley

All of the products have good activity against leaf spot diseases at the 4-5 leaf stage. The mancozebs are protectants and generally are less rain fast than the other products.

The fungicides are often applied in combination with herbicides applied to the crop at these early leaf stages. Some combinations of products may cause slight injury, so herbicide and fungicide labels should be checked before tank mixing. A spreader/sticker addition is not needed for the fungicide, if applied in combination with a herbicide. Also, most manufacturers of the above products have a later season use rate that is generally twice the early season fungicide use rate.

Early season fungicide use rates generally cost approximately $4.00 to $5.00/acre, or less. NDSU research trial responses to this use have ranged from zero (in years and environments not favorable to disease) up to 8 bushels. The greatest economic response from early season fungicide use is seen under the following conditions:

 

CEREAL RUST DEVELOPMENT - SOUTHERN PLAINS

The 3rd edition of the Cereal Rust Bulletin (USDA - St. Paul, MN) indicates that wheat stripe rust infections in the southern US are more severe and extensive than last year due to low temperatures in the last weeks of April. Persistent cool temperatures will favor continued development.

Wheat leaf rust also is common and may increase if temperatures increase. A low incidence of wheat leaf rust was reported in southeastern Nebraska on May 3rd.

Oat crown rust also is developing on susceptible cultivars in Texas. No reports yet of barley leaf rust in the southern plains.

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

 

SOYBEAN RUST UPDATE

Asian soybean rust, Phakopsora pachyrhizi, has been observed only in four Florida counties and one Georgia county this spring thus far. The observations in Florida have all been on kudzu, an alternative weed host, whereas the Georgia observation was made on volunteer soybean. Currently, the disease is not spreading very quickly at these confirmed sites. The progression of soybean rust in the U.S. is being tracked, and is available at the USDA Soybean Rust website and on a special section of the DTN website. The URLs for those sites are:

http://www.usda.gov/soybeanrust/

http://www.dtnsoybeanrustcenter.com/  

Forecasts of soybean rust spore movement from the confirmed FL and GA sites are being made by the North American Plant Disease Forecast Center (North Carolina St. Univ.). These forecasts can be observed at the following URL:

http://www.ces.ncsu.edu/depts/pp/soybeanrust/  

If soybean rust makes it to North Dakota this year, several fungicide products have either full section 3 registrations or section 18 emergency exemptions. Products with section 3 labels include Bravo Weatherstick, Echo, Quadris, and Headline. Section 18 products include Stratego, Tilt, Propimax, Bumper, Folicur, Orius, Laredo, Domark, Quilt, and Headline SBR. Section 3 labels can be found at the manufacturer’s website or at http://www.cdms.net

Section 18 labels for North Dakota may be found at the NDSU Extension Pesticide Program website or at the ND Dept. of Agriculture website which are located at:

http://www.ag.ndsu.nodak.edu/aginfo/pesticid/LabelPage.htm  

http://www.agdepartment.com/Programs/Plant/Section18Exemptions.html

Carl Bradley
Extension Plant Pathologist
carl.bradley@ndsu.edu


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