ISSUE #440

440 - Identification and Control of Cercospora Leafspot

6-26-03

Cercospora leafspot is a constant threat to sugarbeet crop profitability each July, August and September. Late season Cercospora development in September 2002 definitely lowered sugar content in many fields. Model farm data from the American Crystal Sugar Company grower practices database clearly shows three sprays increase revenue per acre in all factory districts on most fields. Four fungicide applications increase on-farm profit especially in fields south of Highway 2.

2003 Cercospora Management Strategies:

  • Scout fields carefully - especially areas favorable to development.
  • Monitor DIV's diligently.
  • Do not cut rates.
  • Watch application intervals carefully.
  • Don't start with the same fungicide class you finished with in 2002.
  • Never use a Strobilurin for Cercospora control more than once per season if at all possible
  • Never use Topsin more than once per season.
  • Always use Topsin in a tank mix.
  • Don't use a Strobilurin first if Quadris was used for Rhizoctonia after the 4-leaf stage.

Other Points to Consider:

  • Consider pre-harvest intervals and early harvest dates.
  • Date of planting has a significant impact on initial incidence and final disease severity. Plant later, spray later.
  • Consider varietal CLS rating when planning a management program.
  • Strobilurin chemistry fungicides are very prone to resistance development.
  • Don't start too early.
  • Don't quit too soon.
  • Fields adjacent to 2002 fields usually develop Cercospora first.
  • Don't use less than label recommended spray volumes and pressures for air or ground application.

Understand Everything About the Disease and Fungicides Today: Table one, on page two, compares the strengths and weakness of all presently registered fungicides. It's imperative every shareholder know each characteristic. Disregard for resistance management will certainly result in loss of effectiveness of ALL available products in the next two to five years.

Table 1: Fungicide Ratings and Information Sheet

FungicideChemical ClassResistance PotentialType of ActivityCercospora ControlRhizoctonia Control
Headline Strobilurin Very High Translaminar Excellent Fair
Gem Strobilurin Very High Translaminar Good Fair - Good
Quadris Strobilurin Very High Slightly Systemic Fair Excellent
Eminent¹ Triazole High Systemic Excellent NA
Topsin Benzimidazole Very High² Systemic Good³ NA
Tinn Products TPTH Moderate² Contact Good³ NA
Mancozeb EBDC Low Contact Fair - Short Residual NA

¹Section 18 approval granted for Eminent in 2003
²Documented laboratory resistance
³Unless field failure levels of resistance are present

Cost Per Day of Control:

Compare your fungicide use strategies on a cost per day of Cercospora control. The 2003 crop has gotten off to a very good start. Don't let late summer Cercospora decrease the yield potential you have worked so hard to establish.

Table 2: Cercospora Leafspot Fungicide Costs, PHI's and REI's

Fungicide***RateCost ($/A)*Appl Int (days)**Cost $/A/dayREI (hours)PHI (days)
Headline 9.0 oz/A $17.38 14 1.24 12 7
Eminent 13.0 oz/A $18.00 14-21 1.29 (0.86) 24 14
Topsin M + Tin .375 lb/A + 3.75 oz. $15.00 14 1.07 48 21
GEM 6.0 oz/A $19.60 10-14 1.96 (1.40) 12 21
Agritin 5.0 oz/A $10.20 10-14 1.02 (0.73) 48 21
Supertin 5.0 oz/A $10.20 10-14 1.02 (0.73) 48 7
Quadris 9.6 oz/A $21.60 7-14 3.09 (1.54) 4 0
Mancozebs 2.0 lb/A $6.00 7-10 0.86 (0.60) 24 14

* Cost includes approximate fungicide product only, NOT application costs; and does not reflect any discounts.Cost ($/A/day) is calculated by cost per acre divided by the shortest (longest) reapplication interval for each fungicide.

** Application interval is shortened, if tolerance is suspected.

*** Always read and follow label directions.

Expanded Weather Station Daily Infection Value Information:

Get daily infections values closer to home in 2003. The daily infection value data will be available from every Red River Valley NDAWN (North Dakota Agricultural Weather Network) weather station in 2003. This information is available at www.crystalsugar.com. Go to agronomy and then "Pest Alert" to access the NDAWN data. A special thanks to Dr. John Enz and his staff at the NDSU Soil Science Department for making this possible in 2003.