ISSUE 5 June 4, 1998
Wheat leaf rust was observed on winter wheat variety trials at Carrington on May 27 and at Casselton on May 28. In both cases the levels were low, with one or two pustules on the lower leaves. On May 29th, leaf rust was observed in spring wheat fields in Ransom and Sargent counties, with incidence of tillers infected ranging from 2 to 48%, with one to two pustules per plant. Surveys of spring wheat in Foster county on June 1 and in Barnes county on June 2 showed similar levels of leaf rust. Spore showers from fields to our south are probably the source of these leaf rust infections. The latest Cereal Rust Bulletin (June 2) states that wheat leaf rust is severe in a few fields of susceptible wheat cultivars in southeastern Kansas and north central Oklahoma. Recent cool weather will temporarily slow development of leaf rust, as optimal temperatures for the leaf rust fungus range from 65 to 85o F. Stem rust has NOT been observed in our crop surveys nor by Dr. Jim Miller, USDA rust pathologist, Fargo.
Septoria fruiting bodies were observed on leaves of winter wheat in Cass Co. The winter wheat crop was in the heading stage, and levels of tan spot, leaf rust and Septoria are still relatively low in this crop.
Trace amounts of barley net blotch were observed in a 4-5 leaf barley field from Dickey Co. Overall, barley and wheat crops are progressing rapidly with minimal levels of leaf diseases at this time. Only wheat on wheat stubble has shown substantial levels of tan spot. Stand problems in wheat and barley, due to a variety of causes including root rot, herbicide carryover, dry seed bed, crusting, wireworm, and even Hessian fly, have been more common so far this spring.
Novartis released a Section 2(ee) label on May 27, 1998, for use of Tilt fungicide on wheat. This 2(ee) label adds some additional diseases to their 24C label for wheat allowing application of Tilt through full ear emergence (Feekes growth stage 10.5). The additional diseases controlled include rusts, tan spot, and powdery mildew, plus the label states suppression (50% control) of Fusarium head blight (scab).
In the last Pest Report information was provided on the Section 18 specific exemption granted for Folicur fungicide for suppression of Fusarium head blight on wheat and barley. I now have a copy of the labels for this use. The specific exemption states that the Folicur may be applied aerially in a minimum of 3 gallons of spray solution per acre. However, Bayer company representative Dallas Rasmussen has indicated to me that the federal label, when approved, will state a minimum of 5 gallons of spray solution per acre to optimize coverage.
Jeremy Pederson, a 1998 NDSU Crop and Weed Science graduate from Ray, ND, was recently hired as a Research Specialist to work on barley production and barley pest problems with Extension Agronomist Mike Peel and Extension Plant Pathologist Marcia McMullen. Jeremy will be working with production research plots, variety plots, and fungicide plots, as well as conducting field surveys to determine crop history effect on barley diseases and other pest problems. This position is funded by the ND Barley Council.
On June 1, Scott Halley started as a Research Assistant in Plant Pathology to work with fungicide application technology. This position is focused on examining various techniques that will improve fungicide deposition and retention on wheat and barley heads for the purpose of suppressing scab. Scott is from Bisbee, ND, and is nearing completion of his MS degree in the Soils Dept. at NDSU. He will be working with several NDSU extension and research staff who are currently working on fungicide application technology. The position was funded by a number of entities, including the NDSU Research Foundation, the Plant Sciences Dept., the Extension Service, the Wheat Commission, the ND Barley Council, the USDA, and several private crop protection companies.
In a 1997 survey of sunflower growers in Kansas, Minnesota, North Dakota and South Dakota, Sclerotinia was the worst disease problem on 10% of Kansas, 47% of Minnesota, 49% of North Dakota and 21% of South Dakota respondents' acres. Sclerotinia head rot was especially serious in Minnesota where it was the worst disease problem on 36% of respondents' acres, but was also the worst disease problem on 27% of North Dakota respondents' acres.
Phomopsis was the worst disease problem on 25% of Minnesota respondents' acres, but was not an important problem in the other states surveyed. Phoma black stem was the worst disease problem on 26% of Kansas, 10% of Minnesota and 14% of North Dakota respondents' acres, respectively.
Crop rotations of at least 4 or 5 years between sunflower crops help reduce the incidence of Sclerotinia wilt in infested fields. Crop rotations to avoid Sclerotinia wilt also must avoid other susceptible crops, such as canola, dry beans, crambe and soybeans. Normal rotations help to reduce the incidence of Phoma black stem.
Both Sclerotinia head rot and Phomopsis are spread by airborne spores, making crop rotation less effective. If either disease has been present in nearby fields in recent years, infection may occur during extended periods of wet weather. Resistance to Sclerotinia is limited. Phomopsis resistant hybrids are grown in many parts of southern Europe and U.S. seed companies are actively developing hybrids with resistance to Phomopsis.
Extension Plant Pathologist
The number of samples in the lab is picking up this week. Fifty-seven samples have been received since the last Pest Report. A majority of these samples are crops such as sugarbeet to be tested for root rot pathogens. Aphanomyces is showing up in many of the samples. Wheat and barley are showing root rot and leaf diseases. Corn, durum, dry bean, sunflower, and soybean make up the rest of the crop samples. The other predominant question on these plants is chemical injury. Chemical inputs are an integral part of farming but they must be used with care and caution. Read labels, thoroughly wash tanks, research the cropping and chemical history of the field, watch wind speed and direction, and do your research before you make decisions about what to plant, what to apply, and when and how to apply it. After all that, if you do suspect injury, be sure to document symptoms immediately. If you have questions about how to properly document, the lab has a bulletin that contains instructions on the documentation process.
Other samples submitted to the Plant Diagnostic Lab include apple, ash, spruce, and pine trees, cotoneaster and juniper, turf, and plant and insect identifications. Much of the injury on the juniper is winter desiccation injury, but there was one confirmed diagnosis of Kabatina tip blight and one of cedar-apple rust. Kabatina tip blight is caused by the fungus Kabatina juniperi and is usually observed in the spring. Dry brown branch tips will have a gray to silver lesion at the base, in which the fungal fruiting structure may be found. Management of Kabatina tip blight is best accomplished by pruning out the dried plant material as early as it is detected and confirmed. Fungicides will not provide protection unless applied in the fall.
Cedar apple rust on juniper is colorful and striking but of little consequence usually. However, the alternate host for the pathogen that causes this disease may be damaged. Gymnosporangium spp. of fungi cause this disease and they require two different host species (juniper and rosaceous hosts such as hawthorn, flowering crabapple and apple) to complete their life cycle. The most serious injury to apples is premature defoliation and fruit distortion. On juniper, Gymnosporangium spp. produce reddish-brown galls that are like gelatinous tendrils in the spring. As the season progresses, these galls will harden off and become woody in texture. Again, this disease is generally serious enough to warrant treatment but there are fungicides labeled on juniper that may provide control in an extreme situation.
Plant Pest Diagnostician