ISSUE 4   MAY 25, 2000

WHEAT DISEASE UPDATE

    Tan spot of wheat was observed this past week on winter wheat and spring wheat in SE counties of ND and in Clay County, MN. I and Dath Mita (new Extension Research Specialist working with me and Mike Peel) observed tan spot on the lower leaves of winter wheat fields in Cass and Ransom counties on May 18. The winter wheat crops were in the early flag leaf emergence stage and tan spot was common but primarily confined to the bottom leaves.

    Virgil Jons, Private Crop Consultant, observed tan spot symptoms in two fields of 1-2 leaf spring wheat in Cass and Clay counties, fields that were planted back into wheat stubble. The tan spot symptoms are small (1/16" to 1/8"), round to oval, and have a dark brown center surrounded by a yellow to tan to reddish halo. Crop and Pest Report #2 had information about control of early season tan spot.   

    Leaf rust and grain aphids were NOT observed in these scouted wheat fields. Kansas is still reporting barley yellow dwarf as their main disease problem, with foliar diseases being light except for south central areas.

    NDSU Extension Circular AE 1148 - Application of Fungicide for Suppression of Fusarium Head Blight (Scab) has recently been revised and will be available through the NDSU Extension Distribution Center and County Extension Offices the week of May 30. The information in the circular provides recommendations for fungicide application techniques for improving control of head scab in wheat, durum, and barley, based on 1998-2000 research results from the field and greenhouse.

    Extension crop scouts will be trained this week at Carrington for procedures in surveying for small grain diseases and insects. They also will assist in a survey of sunflower for early downy mildew detection (see Art Lamey’s comments).

    The crop scouts are Michael Gregoire, operating out of Fargo/Devils Lake under the supervision of Marcia McMullen and Phil Glogoza; Amy Dukart, operating out of the Dickinson REC under the supervision of Area Agronomist Roger Ashley; Jerry Schneider, operating out of the Carrington REC under the supervision of Greg Endres, Area Agronomist; and Holly Semler, Laura Neal, and Alison Marsland, operating out of the NC REC, Minot, under the supervision of Jan Knodel, Area Crop
Protection/IPM Specialist. Amy and Jerry were crop scouts for us last year and we welcome them back. The crop scouts will be surveying in their respective areas for leaf and head diseases of wheat and barley, diseases such as tan spot, Septoria, leaf rust, and scab, and for potential insect problems, such as grain aphids, grasshopper and cereal leaf beetle. They will be surveying fields from the 1-2 leaf stage to hard dough stage.

    The information they gather provides us early warnings of potential disease and insect outbreaks, so that appropriate control measures may be advised. The survey data also provides accurate tracking of pest occurrences and distributions and provides information about potential crop losses associated with these pests. The crop scout efforts are supported by funding from the federal IPM program and from the ND Dept. of Ag. in cooperation with APHIS.

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

CHALKY SOYBEAN SEED, PART II

    The following are some comments of interest from Dr. Marty Draper, extension plant pathologist at South Dakota State University.

    "Vitavax is also effective against white mold and Trace/Gustafson has a new formulation of Vitavax+Allegiance that they are marketing as Stiletto. Vitavax is supposed to be easier on inoculant than Rival is.

    "Also, we had run into a situation about a year ago where the floccose or pubescent tissue on the inside of the pod was adhering to the soybean seed. It looked very much like downy mildew, but no oospores were present and no pathogen could be cultured out. It could have been associated with late maturing seed, but we didn't know for sure."

SUNFLOWER DISEASE SURVEY

    A sunflower disease survey is planned for North Dakota. The survey will be divided into two parts: 1) survey for downy mildew, to be conducted in early June and 2) survey for Sclerotinia, rust, Phomopsis and Phoma, to be conducted in October. Surveyors for downy mildew will be the crop scouts listed in Marcia McMullen’s article in this issue. Cooperators who will survey in October are Roger Ashley, Greg Endres, Terry Gregoire, Janet Knodel, and myself. Dr. Tom Gulya, USDA
sunflower pathologist, may also cooperate in the October survey. We will concentrate on the counties that had the greatest acreage in 1998 and 1999. The June survey will determine the incidence of downy mildew, which will be important as support for a section 18 request for a seed treatment for downy mildew control. The October survey will determine the incidence and severity of the other diseases. This will provide insight on disease prevalence and possible changes since the last survey, conducted by Dr. Gulya.

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

PLANT DIAGNOSTIC LAB

    Apple scab is one of the diseases that is likely to show up again this year due to the fact that there was a high incidence of the disease in the last couple years. It is not too early to begin to look for the disease and begin management programs in apples, crabapples (both flowering and ornamental), and mountain ash. Apple scab is caused by the fungus, Venturia inaequalis, and can cause both foliar and fruit symptoms. Initial infection will follow wet weather and appear as water-soaked spots on the leaves, and subsequently on the fruit. These water-soaked spots will become olive green and velvety, and may
enlarge in a circular pattern. On leaves, secondary infection (infection that results from spores produced in these olive green, velvety lesions) will often follow veins; while on fruit, secondary infections may appear as small spots surrounding the initial infection. Severe infections may result in leaf yellowing and defoliation of the tree. An occasional episode of defoliation is tolerable for a tree, but multiple years of defoliation may weaken a tree resulting in a higher susceptibility to insects, other disease, and environmental stress, and may even shorten the life of the tree. Severe infection of the fruit may lead to cracked fruit, uneven or distorted fruit, or fruit with brown, corky lesions.

    Mountain ash infected with V. inaequlis, will exhibit foliar symptoms similar to apple and crabapple. Premature defoliation of mountain ash trees in central North Dakota has been reported to be 50% in recent years. This is one of the indications that disease pressure may be high this year.

    Management steps for apple scab should include planting resistant cultivars, good sanitation, and appropriate fungicide application. Before planting apples or crabapples, look for cultivars appropriate to the climate and resistant to both apple scab and fireblight. The disease overwinters in leaf and fruit debris so raking up fallen leaves and fruit in the fall is necessary to reduce the potential for new infection the following season. There are many fungicides labeled that will provide protectant activity against the apple scab pathogen. Repeated applications, usually at 7-14 days, will be necessary since infections can
occur throughout the season. The only product labeled for use on apples intended as food is benomyl (Benlate) or captan (Orthocide or Captan). There are numerous products for use on ornamental crabapples - propiconazole (Banner Maxx), thiophanate methyl (Cavalier), trifloxystrobin (Compass), chlorothalonil (Daconil, Manicure Flowable, Twosome Flowable), mancozeb (Dithane, Junction, Flowable Mancozeb, Fore), muclobutanil (Eagle, Systhane), and maneb (Pentathalon). The only products with mountain ash on the label were Cavalier and Junction. Always check the label for specific listing of the host and disease to be treated, and follow all label recommendations and instructions.

Cheryl Ruby
Plant Diagnostician
diaglab@ndsuext.nodak.edu