ISSUE 8 June 23, 2005
GENERIC TEBUCONAZOLE FUNGICIDE
Several weeks ago, Folicur fungicide (tebuconazole) received a Section 18 emergency exemption for use on wheat and barley in ND. Although Folicur has not yet received a full federal label for wheat and barley, it is already off patent, and generic tebuconazoles are being produced. Orius, a generic tebuconazole produced by Makhteshim AGAN, is labeled for soybean rust in ND, under a Sec. 18 quarantine exemption. However, the ND Dept. of Agriculture has NOT approved a Sec. 18 for Orius on wheat and barley, so at this time, there is no generic tebuconazole registered for use on wheat and barley in ND. I am testing three generic tebuconazoles this summer in research plots at Fargo to get information on how the generics perform in relationship to Folicur.
SCAB SPORE COUNTS
The NDSU small grain disease forecasting web site is predicting high risk for scab infection in much of the state, based on temperature, rainfall, and relative humidity favorable for spore production. However, the model doesnít tell you IF spores have developed and are present in the atmosphere. With winter wheat flowering or have already flowered and some spring grains soon at the growth stage for fungicide decisions, the question is, are scab spores now in the environment? The answer is, we donít know. NDSU researchers will have a spore trap in Fargo, to tell us if any spores are in the atmosphere here, but this trap will not provide information for other locations.
ND IPM SURVEY RESULTS, 6-13 through 6-17
NDSU IPM field scouts surveyed 136 wheat fields and 23 barley fields the week of June 13-17. Kelsey Steenblock, scout for the SE and EC region had a devil of a time getting into fields in her scouting territory because of heavy rains during the week and the heavy soils of the region, but the other scouts were generally successful in scouting their territory.
Tan spot was commonly found throughout the state, but highest severities were reported in counties in southwest ND (see figure of tan spot severity).
Leaf rust was observed in 28% of the wheat fields surveyed, with severities in the 1-5% range most common (see figure of wheat leaf rust severity).
Field scouts also observed stripe rust in 18 wheat fields surveyed, primarily in the southwest region (see figure of stripe rust incidence).
Grain aphids were found in 15.4% of the wheat and 13.0% of the barley fields surveyed, and barley yellow dwarf (BYDV) symptoms are also being observed. The highest percent of tillers with aphids was 22%, in one wheat field in Morton county.
In barley, approximately half the fields exhibited either spot blotch or net blotch symptoms. During the week of June 20-24, the NDSU field scouts will also start looking for soybean aphid in soybeans and the extent of sunflower beetle and downy mildew damage in young sunflower fields.
Weekly maps of disease occurrences in crops surveyed this year can be found at the following web site:
Darla Verbitsky, Extension Administrative Secretary in Plant Pathology, and Justin Knott, Pest Survey specialist with the ND Dept. of Agriculture, have worked together to provide these weekly map updates on the ND IPM web site.
DISEASE REPORTS FROM NEBRASKA AND SOUTH DAKOTA
Plant pathologists from Nebraska report that stripe rust is common in their winter wheat and many farmers are spraying fungicides to control this disease. In South Dakota, Jeff Stein and Marty Draper report that stripe rust is most severe in the winter wheat variety Nekota. High temperatures of this week may halt spore production of stripe rust.
A low level of Fusarium head blight (scab) was observed in several winter wheat fields in South Dakota, from the far southeast corner of the state. Black chaff bacterial infection on glumes of wheat heads was also observed in some winter wheat fields.
NDSU Extension Plant Pathologist
NDSU PLANT DIAGNOSTIC LAB-HERBICIDE INJURY
As previous crop and pest report articles have indicated, our recent cool, wet weather has been particularly favorable for many diseases that affect crops and ornamental plants. The Plant Diagnostic Lab has received over 650 samples so far for fiscal year 2005. This is about a 30% increase over the number of samples received last year through June. Diseases that have been seen in the lab recently include downy mildew on sunflower, tan spot on wheat, wheat streak mosaic virus, barley yellow dwarf virus, Rhizoctonia crown rot (alfalfa), Rhizoctonia brown patch (on turfgrass), Pythium root rot (sugarbeet, soybean), and Aphanomyces root rot on sugarbeet. With the excess moisture that many North Dakota soils have experienced recently, root rot diseases and other soil-borne diseases are expected to flourish. Several crop samples that have been submitted during this growing season have showed symptoms consistent with herbicide or other chemical injury, from misapplications, uncooperative weather, or drift events.
Samples that exhibit symptoms that are consistent with herbicide injury (or injury from other chemicals) comprise a significant proportion of samples that are evaluated by the lab. The NDSU Plant Diagnostic Lab evaluates such samples visually (not chemically), for a $15 fee for North Dakota residents and a $25 fee for non-residents. A visual assessment of plants suspected to exhibit symptoms of herbicide or other chemical injury can be valuable for at least two reasons. It can determine if the symptoms are consistent with herbicide injury, and if so, the injury can usually be associated with a specific group of herbicides. Often, a visual assessment by a third party, such as the NDSU Plant Diagnostic Lab, may be sufficient for neighbors, applicators, or others involved to resolve potential conflicts. Furthermore, by narrowing the possibilities with a visual assessment, the expense of chemical analysis, if warranted, can be reduced, because the possibilities can typically be significantly narrowed. If chemical analysis is needed, several laboratories are capable of testing for herbicide or other chemical residue in plant tissue or soil, and a partial list of such laboratories can be found at the NDSU Plant Diagnostic Lab website:
If you have any questions regarding herbicide injury, visual assessments, or laboratories that can provide chemical analysis services, feel free to call the NDSU Plant Diagnostic Lab (701-231-7854) or e-mail the lab (firstname.lastname@example.org).
SOYBEAN RUST FOUND IN NEW FLORIDA COUNTY
Soybean rust was recently found in Jefferson County, Florida on kudzu. This is the fifth county in Florida to report having soybean rust in 2005. All findings of soybean rust in Florida has been on kudzu, which is an alternative weed host. Georgia is the only other state to report having soybean rust thus far in 2005. The Georgia find was in only one county on volunteer soybean.
Because soybean rust has not yet become widespread in the southern U.S., it is becoming more likely that North Dakota growers will not have to deal with this disease this season. Soybean fields and soybean rust sentinel plots are still being scouted for soybean rust in North Dakota and other soybean-producing states. For more information about the presence of soybean rust in the United States, visit the USDA Soybean Rust Monitoring Maps at:
FUNGICIDES FOR SCLEROTINIA STEM ROT OF CANOLA
With canola near to or beginning to bloom in parts of the state, its susceptibility to Sclerotinia stem rot increases. The airborne spores of the Sclerotinia fungus use dead flower petals as an energy source which allows them to cause infections on the canola plant. Before any of these airborne spores can be produced, mushroom-like structures of the Sclerotinia fungus known as apothecia must be present in the soil. These apothecia arise from sclerotia in the soil when the environment is favorable. Soil moisture is a key component to this favorable environment, as the soil must be at or above field capacity for 10 to 14 consecutive days for apothecia emergence to occur.
Apothecia of the Sclerotinia fungus
(J. Venette, NDSU)
Fungicides registered for management of Sclerotinia stem rot in canola include Ronilan, Topsin M (and generics), Endura, and Quadris. From studies conducted at NDSU and the University of Minnesota, Ronilan, Topsin M, and Endura have provided the most consistent control. These products should be applied when canola is between 30 to 50% flowering.
To help with spraying decisions, a Sclerotinia risk map is available (see Crop & Pest Report No. 7) at two websites:
http://www.northerncanola.com/ & http://www.ag.ndsu.nodak.edu/aginfo/sclerotinia/sclerotinia.htm.
The most recent map (June 20) shows that the majority of North Dakota is under moderate risk.
A fungicide application may be most beneficial if:
Carl A. Bradley
Extension Plant Pathologist