Spring wheat growth and maturity is on the fast track. Plant maturity is being pushed ahead of schedule in many parts of the Valley. According to Doug Holen, Regional Extension Educator in Fergus Falls, rain has been a near daily occurrence in many locations in west central Minnesota. Showers have been localized up and down the Valley this year. Many producers in the Crookston area are watching the sky wishing for rain. Disease issues vary somewhat depending on the crop’s location and history of rainfall.

Disease Update
Doug Holen reports that tan spot, caused by Pyrenophora tritici-repentis, is a common foliar disease in many wheat fields where rain has been periodic. He identified leaf rust, caused by Puccinia triticina, from a field near Comstock as well as powdery mildew, caused by Erysiphe graminis, from a field near Carlyle. The disease can be found at low severities in the On-Farm Disease Management Trial located east of Breckenridge as of June 19. Powdery mildew is widespread this year. Ardell Knudsvig, Minnesota Dept. of Ag Pest Surveyor also reports it from fields located in east Polk. Meanwhile, leaf and stripe rusts are known as far north as Polk County. Lorilie Atkinson and Heidi Michaels of the extension plant pathology program identified both rusts at the On-Farm Disease Management Trial located near Oklee/Brooks the week of June12. Stripe rust is established in localized hot spots, called foci, but leaf rust pustules were slight and scattered. See the Minnesota Pest Report online for more disease and insect survey information:

 http://www.mda.state.mn.us/pestsurvey/pestreports/default.htm

Powdery Mildew

This pathogen can overwinter in infected wheat residue or in live tissues of winter wheat. It produces two types of spores (ascospores and conidia) that spread the disease to healthy plants via wind. Unlike other leaf diseases, these spores don’t need moisture for infection - they only need high humidity (e.g.: 85-100%). Diseased leaves have white tufts of fluff (Fig. 1) that eventually turn light tan in color. The powdery tufts contain the next generation of microscopic spores, or conidia, that will be carried by air currents to infect other plant tissues. If conditions are right and the disease develops early, yield losses can result. Watch the lower canopy for the disease and know how quickly it is developing. If the crop has a lush thick canopy, an application of fungicide may be needed. Most areas that I’ve seen the disease are under plant stress from the lack of rain and many canopies are open. Plant growth stages vary from heading to flowering. In general, growers are applying fungicide for scab at that timing anyway if the crop merits protection.

Fusarium head blight (scab)

The wheat crop is getting close to heading or is already flowering in many areas. Producers are trying to decide whether to apply a fungicide this year. Here are a few things to consider:

• Wheat, barley and corn residues increase the in-field and local supplies of scab inoculum, increasing the potential for disease development.
• Identify the level of scab resistance in your variety to identify your crop’s level of risk for an epidemic.
• Consider the frequency and amount of rain received 1-2 weeks before flowering. Fusarium spores are produced on residue on the soil surface. If residues stay moist over an extended period, chances are greater that spores will be produced in time for flowering. If the soil surface and residues are dry, the risk is reduced.
• Does the crop’s yield potential make fungicide application an economically sound decision?
• What does the Minnesota Fusarium Head Blight Epidemic Risk Forecasting System predict for your area? This year, model predictions are based on humidity levels and the disease resistance levels in wheat varieties. Try inputting flowering dates prior to the actual date that your crop will flower to identify whether the trend is for more or less disease when your field is actually flowering. The system can be accessed online at:

http://mawg.cropdisease.com