ISSUE 6 June 8, 2006
NDSU DISEASE FORECASTING SITE
The NDSU forecasting site reflects the spotty rain showers that have occurred across the state the past week. Those NDAWN stations that reported some substantial rain fall are reporting YES for conditions favorable for tan spot and/or leaf rust infection. For those sites that are dry and missed any good rainfall accumulations, the forecasting models indicate NO for risk of these fungal leaf disease infections.
Winter wheat across many areas is approaching or in the flowering stage now. Few, if any, NDAWN sites are currently reporting favorable conditions for Fusarium head blight infection. These are current conditions, and return to rainfall patterns can change the forecasting recommendations rapidly.
WHEAT LEAF RUST FOUND IN REGION
Independent crop consultant, Virgil Jons, found wheat leaf rust at trace levels in a field of Oklee spring wheat in Clay Co., MN on Tuesday, June 6th. Oklee is moderately susceptible to leaf rust. Virgil found the rust pustules on leaves in a double seeded headlands area along a shelterbelt, and the canopy in this area was thick and had dew present in mid-morning. He also saw an active lesion of stripe rust in this field. Matthew Leiphon, the NDSU IPM field scout in the northeast region, also found trace levels of wheat leaf rust on June 6th, on two winter wheat fields in Benson Co.
These rust observations indicates that rust spores have made it to the area. Development in individual commercial fields will depend on rainfall, duration of dews, and susceptibility of the variety.
Wheat Leaf Rust
NDSU IPM SURVEY EARLY RESULTS
NDSU IPM’s summer field scouts surveyed 233 wheat fields and 22 barley fields the first full week of survey. Diseases were almost absent in the barley fields scouted. In wheat, the tan spot symptoms were the most common observation, with incidence of plants showing symtpoms ranging from 9 to 30% and severity ranging from 1-5%.
The scouts have observed just a few fields with barley yellow dwarf symptoms and only a few with a single grain aphid.
Extension Plant Pathologist
DOWNY MILDEW ON CANOLA
A severe case of downy mildew was recently found on canola in a field in northwestern Minnesota. This was the first time that downy mildew on canola has been observed in the region (at least at this magnitude). Typically, cool and wet weather is most favorable for the pathogen that causes downy mildew (Peronospora parasitica). The canola downy mildew pathogen is different than the sunflower downy mildew pathogen (Plasmopara halstedii) and affects only canola and other brassicas, although the symptoms are certainly similar to that of downy mildew on sunflower. Symptoms of canola downy mildew appear as yellow rounded lesions on the upper leaf surface with a white cottony growth on the underside of the leaf (see figure). According to the book "Diseases of Field Crops in Canada", symptoms may be conspicuous at the rosette stage, but the disease will usually disappear as temperatures rise in the summer, and effects on yield and quality are not significant. Because this is a new disease to our region, I would like to be alerted of any other outbreaks.
Symptoms of canola downy mildew on the
lower (left) and uppper (right) leaf surface.
Carl A. Bradley
Extension Plant Pathologist