Plant Pathology for May 11, 2000

The latest Cereal Rust Bulletin (May 8) indicates that wheat leaf rust severities in north central Texas and extreme southern Oklahoma ranged from 20-80%. Leaf rust in southern Kansas ranged in severity from trace levels to less than 20%, not much change from last week. Rust will continue to develop in these states if warm weather and moisture occur.

The latest Kansas State Plant Disease newsletter (May 4) indicated that barley yellow dwarf virus (BYDV) is the number one problem in wheat in that state this spring. It is most serious in southeast and southcentral Kansas. Kansas State’s Extension Plant Pathologist Bob Bowden states that the primary control for BYDV for winter wheat is late planting. For spring wheat, barley and oats, the primary control is EARLY planting, so we may be in luck this year, with susceptible crops developing substantially before grain aphid populations are detected in the state. Dr. Bowden states that chemical control often requires multiple applications on a preventative schedule, because significant virus transmission may have already occurred by the time
aphid populations are detected; multiple insecticide applications rapidly become non-economic.

Recent rains across much of the state may trigger development of the tan spot fungus and subsequent early season tan spot symptoms on wheat. The symptoms may develop on crops as young as one leaf, if wheat residue is present on the soil surface and the residue remains wet long enough for fungal development and spore release. Symptoms are round spots with the typical dark brown center surrounded by a yellow halo, or if temperatures are quite cool, the fungal spot may appear with a reddish to purplish halo.

Fungicide control of early season tan spot may be warranted IF the following conditions apply:

* The wheat stand is good and crop looks like it is off to a good start (except for the tan spot present)

Fungicide	Rate/acre for early season control	Suggested retail price
Mancozebs (various trade names and formulations)	1 lb	$2.40- $2.60
Tilt	2 fl oz	$4.25

The labels of the above two fungicides allow early season application, prior to jointing. They generally are applied in the 4-5 leaf stage, and they may be tank mixed with herbicides commonly applied at this growth stage of the wheat crop. Please check the labels for tank mix restrictions. Certain herbicide products have restrictions against the tank mixing of fungicides (see Sec. A14 of the NDSU Weed Control Guide, information on herbicide-fungicide restrictions at the internet site):

The Maxim 4FS label has been expanded to include crambe, flax and safflower. Maxim provides effective protection against Rhizoctonia, Fusarium and Helminthosporium. It also provides protection against Aspergillus and Penicillium; these may attack and damage seed sitting in dry soil for long periods of time. Maxim is not for planter box application or other applications that may occur immediately before planting

STATE LABELS ISSUED FOR BRAVO ZN, BRAVO WEATHER STIK AND BRAVO WEATHER STIK ZN ON POTATO

State labels have been issued for Bravo Zn, Bravo Weather Stik and Bravo Weather Stik Zn on potato. The state labels allow for application up to 21 ½ pt/A of Bravo Weather Stik or Bravo Weather Stik Zn or 30 ½ pt/A of Bravo Zn (16 lb ai) per acre per season on long-season varieties, such as Russet Burbank, Russet Ranger, Shepody, Snowden, FL 1533 or Monona.

The Environmental Protection Agency granted a section 18 for the use of Eminent on sugarbeet for the 2000 growing season to control Cercospora leaf spot. Eminent is to be used at 13 fl oz/A, with no more than 6 applications made per season. It is to be applied in alternation with a product with a different mode of action. At present, TPTH (Super Tin, Agri Tin) or mancozeb can be used to alternate with Eminent. TPTH can be used on a 10-14 day interval with Eminent; Eminent should be used on a 14 day interval. Alternation between classes of chemistry and modes of action is essential for the management of fungicide resistance in Cercospora.

The Environmental Protection Agency granted a section 18 for the use of Tilt on dry bean for the 2000 growing season to control dry bean rust. Tilt is to be used at 4 fl oz/A with repeat applications on a 14 day schedule. Tilt is not to be applied within 28 days of harvest. Tilt is locally systemic and has up to 4 days of post-infection activity. However, for the purposes of resistance management, Tilt is best used as a protectant fungicide. All varieties of pinks and small reds are susceptible to rust.
Most older pinto varieties are also susceptible. Newer pinto varieties that are resistant to current rust races include Apache, Burke, Buster, Chase, Elizabeth, Focus, Frontier, Kodiak, Maverick, Montrose, Remington, UI-320 and Winchester.

Northarvest Bean Growers Association: http://www.northarvestbean.org. This site contains the current and past issues of the "Northarvest Grower Magazine".

Pulse Crop Diseases: http://paridss.usask.ca/specialcrop/pulse_diseases/index.html. This web site of the University of Saskatchewan provides information on diseases of chickpeas, lentils and field peas, with photos, a discussion on disease biology and management, and spray decision guides. Keep in mind that only sulfur is registered for use on field pea in the U.S., no fungicide is registered for use on lentil in the U.S., and no fungicide is currently registered for use on chickpea in the U.S. ( the Bravo label should be expanded to include chickpea by this summer, however).

Soybean Plant Health: http://www.plantpath.wisc.edu/soyhealth. This Web site is managed by the Plant Pathology Department, University of Wisconsin. It contains information on recent research, health bulletins and links to other sites.

The Plant Diagnostic Lab hit the ground running this year, with a new database, new billing system, and plenty of samples already processed. The lab officially opened on April 3, 2000. After seeing more than 500 samples of rotting potatoes last fall, it was great to see some tree and ornamental samples that would recover. Samples and diagnoses for the year include: potatoes (PVY, PLRV, scab, silver scurf); spruce (Rhizosphaera needlecast, spider mites, Cytospora canker); pine (Sphaeropsis tip blight); pansy, petunia, vinca (salt buildup, poor quality irrigation water); geranium (spider mites, salts injury); Dracena (spider mites); turf (necrotic ring spot, pythium decline, patch disease complex); canola (unidentified insect damage); tomato (TSWV); insect ID; soil (negative Pursuit residue).

As a reminder, the lab is handling soil samples for imazethapyr (Pursuit) residue testing and plant samples for glyphosate (Roundup) injury. Both tests cost $150.00. This is an increase in the cost of the imazethapyr test due to an increase in reagent costs. Soil samples should be about a gallon in volume and represent 4 sites in a quarter, from 0-6". Be sure to thoroughly mix the soil composite.

The Plant Diagnostic Lab also offers insect and plant identification, disease diagnosis, visual herbicide injury diagnosis, cultural information, and control recommendations. To submit a sample, collect as much of the living plant as possible. If possible, send several plants showing similar symptoms; and include a "healthy" plant for comparison. For tree samples, send one or several branches showing the symptoms of concern. If possible, take a branch with both injury symptoms and some green, healthier material. Leaves from any plant should not be wrapped or packed with wet paper toweling of any kind.
Simply place the leaves between pieces of paper. Root masses are the only part of a plant that may be wrapped in plastic, but never seal a plastic bag. Insects are best sent in vials of alcohol or placed on loose packing material in a box. Please don’t send live insects in the mail for identification.

Samples may be submitted with a Plant Diagnostic Lab Form. If a form is not available to you, include your name, address, phone number, email address (if appropriate), and a written narrative that contains field or planting history, pesticides and fertilizers applied, age of the plant, when symptoms were first observed, and any other information that may be relevant. A more complete history and narrative will make it possible for the lab to provide a more thorough and specific response.