Growers Reminded to Inspect Peas for Disease

EDMONTON - Aug 5/04 - SNS -- Alberta Agriculture strongly reminded field pea producers to inspect their fields for signs of powdery mildew, downey mildew and ascochyta in field peas on account of this year's extreme weather conditions.

"Powdery mildew ravaged non-resistant varieties of field pea in 2003 due to the lack of summer rains accompanied with hot days and dewy nights," says Karla Bergstrom, crop specialist with Alberta Agriculture, Food and Rural Development, Stettler.

"Areas of the province that have significantly drier conditions this season are reporting early signs of the disease. The concern is that a few white spots on the topside of the lower leaves can cover a field very rapidly.

" Powdery mildew causes problems at harvest because it prevents natural dry down and reduces the effectiveness of desiccation because the chemical cannot penetrate the mildewy growth that covers the entire surface of the plant. The long dry fall in 2003 was the only reason that producers who did not spray a fungicide were able to harvest infected fields."

Choosing resistant varieties or spraying a fungicide is essential at the early developmental stages of this disease because it spreads very quickly. There are two fungicides registered for powdery mildew on peas, Kumulus DF and Headline. These products are protectants not cures: to be effective, they must be applied before the crop is white.

"Downey mildew is also infecting fields this year, but this disease is not usually a threat in Alberta," adds Bergstrom. "It develops in cool, wet conditions. Alberta producers have not experienced extensive damage from this disease in the past. In the field, it looks like fluffy, grayish-white or mousy brown growth on the underside of the pea leaves that causes the top of the leaf to brown.

"Product research in other parts of the world has been effective on this pathogen, but there is nothing currently registered in Canada. Following a good crop rotation and seeding with disease free seed are suggestions to keep this disease manageable."

Ascochyta mycosphaerella blight is another leaf disease that greatly affects pulse crops. Symptoms in field pea have been slow to appear this year because of cool temperatures, but with the heat in mid-July, the disease pressure will be building. To stay ahead of this disease, producers should be scouting their fields. Healthy plants can be infected by ascospores from rain splash and wind. When scouting, look for small brown to purplish irregular flecks appearing on leaves, stems, tendrils and pods. Bravo and two new fungicides, Headline and Lance, are available for control.

Ascochyta will cause yield and quality loss because of reduced seed set and shriveling. Often the effects of the disease at harvest are overlooked in the decision to apply a fungicide. Standability is reduced as the lesions grow together causing lodging or even girdling in the stem, making harvest difficult.

A new tool for producers is available on Alberta Agriculture's web site to help make the decision to spray; it is the Ascochyta Scoring System developed by Ken Lopetinsky, pulse research agronomist, Alberta Agriculture, and Sheryl Strydhorst, PhD candidate in pulse agronomy, University of Alberta. This web program bases fungicide application on the crop canopy, leaf wetness, percentage of plants showing symptoms and the weekly weather forecast.

"Early detection for all leaf diseases is always your best prevention," says Bergstrom. "Timely scouting is key to making informed decisions for controlling these diseases."