ISSUE #555

555 - Cercospora Control and Resistance Management

6-29-11

CERCOSPORA LEAFSPOT INCIDENCE AND SEVERITY INCREASED DRAMATICALLY IN 2010 COMPARED TO RECENT YEARS. THIS WAS particularly apparent in the southern Red River Valley. Early planting, above average temperatures and well above normal relative humidity levels caused many favorable infection periods for disease. Cercospora was found in early July in the Moorhead and Hillsboro districts and by mid to late July in Crookston, East Grand Forks and Drayton districts. Numerous fields reached economic loss levels by mid-August in the Moorhead district. Inoculum levels will be much higher in 2011 than they have been for many years.

Multiple Spray Program Equals More Profit

Three and two spray programs almost always increase revenue over just one or zero spray programs, see graph 1. One, two and three sprays increased revenue by $145, $298, and $373/acre compared to not spraying.

555.1

Strategies for 2011 Cercospora Control

  • Plan your management program based on a late August application of Headline
  • The first fungicide application should be a triazole, (Inspire, Proline or Eminent). NOTE: Eminent is not recommended south of Highway 200 because of reduced Cercospora Leafspot control in this area in 2010.
  • In a three spray program follow the triazole with tin or a tin plus Topsin tank mix, and then apply Headline.

  • Late May and June planted fields may only require two sprays. Use your triazole of choice followed by a Headline application

555.2

Resistance Management Strategies

  • Don't use a class of fungicide more than once per year.
  • Don't use Eminent alone in the southern RRV, use it in a tank mix if at all.
  • Don't use a one spray program.
  • Don't use lower than label rates of any product
  • When using a one spray program in back to back years alternate between Headline and Inspire.

Factors Increasing Risk of High Incidence and Severity of Cercospora

  • Early planting
  • Planting varieties with higher leafspot ratings
  • Shorter rotations
  • Planting adjacent to fields with high inoculum from 2010
  • Starting spray programs too late
  • Using improper application techniques

Remember to Contact your Agriculturist for Assistance