ISSUE #472

472 - Resistance Management Maximizes Long-Term Profit


Cercospora leafspot management programs must focus on BOTH disease control and fungicide resistance management in 2005. Growers must develop management plans to effectively achieve these objectives this year. Failure to do so will result in 1) serious increases in fungicide resistance, 2) loss of effectiveness of fungicides, 3) increased cost of cercospora control, 4) lower yield and quality, and 5) lower on-farm profits.

Failure to properly manage fungicide resistance and cercospora control in 2005 will have costly consequences for many years to come. NO NEW FUNGICIDES ARE BEING CONSIDERED FOR APPROVAL BY EPA AT THIS TIME.

Field Samples Collected in 2004 Indicate

  1. Resistance to Topsin remains very high, about 75% of samples are resistant.
  2. Tin resistance is the lowest it has been in over 10 years.
  3. Eminent resistance has dramatically increased. Ten percent of the fields sampled showed high resistance and another 26% showed partial resistance.
  4. Resistance to Strobilurin fungicides if Eminent is mismanaged will increase rapidly.

2005 Cercospora Management Recommendations

  1. Pay careful attention to resistance data. Each agriculturist has resistance maps of the Red River Valley area.
  2. Rotate fungicides throughout the season.
  3. Give priority to resistance management whenever compatible with disease control.
  4. Tin fungicides should be a very integral part of cercospora control at about ½ the cost of other products.
  5. If at all possible use only one Strobilurin (GEM or Headline) per year.
  6. If more than one Strobilurin must be used, then only use one Headline and one GEM and keep them as far apart in the spray program as possible.
  7. Never use Topsin alone and never more than once per year.
  8. Use enough water volume to maximize disease control with ground sprayers. The minimum use should be 10 gpa, with at least 15 gpa preferred and no need to exceed 20 gpa.
  9. Spray air systems can do an excellent job of cercospora control. Follow label recommendations with spray air equipment.
  10. Cercospora inoculum is as low as it has been since at least 1998.
    • The amount of inoculum present will determine how quickly disease onset occurs.
    • First fungicide applications may be delayed depending on disease onset and Daily Infection Value data. Fields must be monitored if spraying is to be delayed.
    • Later spray initiation removes the need to stretch spray intervals and increases the chance for a late fungicide application which will promote best late season benefits.
    • Couple low inoculum levels with date of planting, variety resistance rating, fungicide resistance data and local disease history to develop an effective 2005 control strategy.

For more information see your Agriculturist, the 2005 Pocket Production Guide and the 2004 Sugarbeet Research and Extension Reports.

Access the NDAWN website for current information on weather conditions favorable for disease development.


Special Eminent Recommendations for 2005

  1. Never use Eminent more than once in 2005 in any field.
  2. Never use Eminent as the only spray on a field in 2005.
  3. Never stretch Eminent spray intervals beyond 14 days.
  4. Consider not using Eminent in any field adjacent to or near a field known to have high Eminent resistance in 2004.
  5. In areas with Eminent resistance consider substituting a Tin, Tin + Topsin or a Strobilurin for Eminent.
  6. Use Eminent only if a 3 or 4 spray program is needed due to early disease onset.
  7. Use Eminent first (possibly second in a 4 spray program) if it must be used so subsequent sprays can control any resistant isolates that might be present.

Layby Herbicide

Don't forget Layby herbicide use on late or replanted fields with low plant populations. 

* Usually only 1 to 5 fields showed resistance in any given township.