457 Control Cercospora To Protect Crop Potential
Cercospora Leafspot control is the last key crop management practice to accomplish prior to harvest. Effective Cercospora control maximizes 2004 crop yields and quality. Cercospora-free beets also store and process better. The three key facets of Cercospora control are: Using the RIGHT fungicide at the RIGHT rate and applying them with the RIGHT timing. Doing these three things RIGHT will result in cost-effective disease control.
Factors Influencing Cercospora Management
- Planting Date - don't start spraying all fields at the same time
- Variety CLS Rating - very resistant varieties may require one less spray
- Onset of Disease - scout fields to know when disease is first present
- Rotation Length - long rotations often have lower disease severity
- Spray Volume - all fungicides perform better applied at labeled spray volumes Headline, GEM, Tins, and Mancozebs especially need higher spray volumes
Table 1: NDSU Water Volume Trial, 2003, Breckenridge, MN*
|Treatments||Recoverable Sucrose/A||CLS Rating KWS Scale|
|20 gpa + fungicides
|15 gpa + fungicides
|10 gpa + fungicides
|7 gpa + fungicides
* Courtesy Dr. Mohamed Khan - Extension Sugarbeet Specialist - NDSU
Choosing the RIGHT Products
- Always alternate between fungicide classes
- If Quadris is used for Rhizoctonia, don't use Headline or GEM as your first application. See Table 2 for detailed information on all registered fungicides
Choose The RIGHT Rate
- Apply all fungicides according to labeled rate requirements.
- Use of full label rates is highly recommended.
- Don't extend interval between fungicide applications beyond label requirements if disease is present.
Apply Fungicides at the RIGHT Time
- Start fungicide applications at the onset of disease in your fields or your piler district
- Eminent is the only fungicide with significant "reach back" activity and it's only 3-4 days
- Maintain disease control through most of September - European research has documented 4%-8% yield increases, maintaining a healthier vigorous canopy until harvest. U of MN research by Dr. Larry Smith has also observed yield benefits from full season disease control
Table 2: Cercospora Leafspot Fungicide Rates, Re-entry and Pre-harvest Intervals
|Fungicide||Rate||Application Interval (days)||Re-entry Interval (hours)||Pre-harvest Interval (days)|
|Topsin M + TPTH
||.375 lb/A + 3.75 oz.
Cercosopora Resistance Management
Each year American Crystal Sugar Company agriculturists collect nearly 800 samples of beet leaves with Cercospora from grower fields. NDSU plant pathologists Dr. Gudmestad and Dr. Secor analyze these for the presence of resistance to Eminent, Tins, Topsin, and Headline. Analysis for GEM will be initiated in 2004.
"Analysis of 2003 field samples has documented the presence of resistance buildup for Eminent and Headline fungicides."
All shareholders must carefully follow accepted resistance management strategies if we are to continue to successfully control Cercospora. Minnesota and North Dakota growers failed to follow these strategies in the early 1980s. As a result Benlate, Mertect, and Topsin were rendered totally ineffective for Cercospora control in just a few years. Yield losses of up to 50 percent were experienced.
Key Resistance Management Strategies
- Timely first spraying
- Don't reduce fungicide rates
- Rotate fungicide classes
- Don't stretch application intervals too far
- Use Eminent once per season where NDSU data indicates risk for resistance is increasing
- Use only one strobilurin product (GEM or Headline) per season if at all possible
- Consider starting 2004 with a different product than the last one applied in 2003
- Tank mixing fungicides is very effective
Cercospora Advisory Available
The NDSU NDAWN Cercospora Leafspot Advisory System has been improved for 2004. Go to www.crystalsugar.com, then agronomy, then Pest Alert to access this daily information.
Contact your agriculturist
for maps showing section-by-section incidence and severity of resistance to each fungicide from 2003 NDSU data in your growing area.
Watch For Rhizomania In July and August
Will strange bright yellow spots show up in your fields in 2004? Many fields in the Red River Valley have had fairly severe rhizomania in the past. Affected fields could have reduced tonnage and sugar content. Roots infected with rhizomania don't store or process well either.
Rhizomania Identification and Symptoms - Leaves
- Patches in fields
- Poor growth
- Bright, almost fluorescent yellow leaf growth
- Narrow long leaves
- Longer than normal and erect petioles
- Photo #1
- Often shows up in poorly drained spots first
I.D. and Symptoms - Roots
- Stunted tap roots
- Masses of hairy sideroots or a "bearded" appearance on the tip of the beet
- Root growth constricted a few inches below the soil - "wineglass" shape
- Yellow to dark brown discoloration of root tip vascular bundles
- Photo #2
- Wet, warm to hot conditions increase disease severity and incidence
Rhizomania Control Measures
- No seed treatments are available
- Sanitation of field equipment
- Planting early minimizes impact
- Improved field drainage reduces severity
- Longer crop rotations may help
- Soil fumigation - but it's cost prohibitive
- Resistant variety use
- Tare soil management
If you suspect you might have rhizomania in a field, contact your agriculturist for assistance making a positive identification. Once rhizomania is found, it's very important to monitor disease severity changes in the field. Incidence of the disease is most common south of Highway 2 at this time.
Informational Brochures Available
American Crystal has two excellent information resources to help growers understand and identify the disease. Contact your agriculturist for a copy.
- Quick I.D. Reference Card
- Rhizomania in the Red River Valley Brochure
Using Satellite Imagery Now Easier
New updates to the SATSHOT satellite imagery webserver through the American Crystal website are now available. Growers can now access any field of theirs through the system. The speed of accessing imagery from the web has also increased dramatically allowing the grower to spend less time accessing the imagery. Multiple imagery dates are available for each of the last 10 growing seasons. New searching and navigation tools on the website make it quicker to find your field and access the satellite image file. Also, new grower log-in features allow the agriculturist to also access the same field the grower downloads.
Also being released are new LandScout software tools provided by Agri ImaGIS Technologies to build variable rate application (VRA) maps for the sugarbeet top imagery program. The grower can now build his own VRA map in minutes to be utilized in many different brands of application equipment. Desktop LandScout versions for analyzing the imagery and PDA Pocket LandScout software for variable rate fertilization in your GPS-equipped implements are also available. For more software information, contact John Illich at Agri ImaGIS Technologies - 701-235-5767 ext 223 or firstname.lastname@example.org.
Variable Rate Fertilization Increases Profit
Every share-holder needs to consider if zone soil sampling and variable rate N application may be of benefit for each field. American Crystal data shows increased on-farm profit of about $45/acre using this practice. Make plans now with your consultant, fertilizer dealer, or agronomist to see what benefits could be realized in 2005.