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2013 PESTICIDE GUIDE
Insect Management
  • Aphids A Problem in 2012
  • Insecticide Chart
  • Insecticide ID Guide
Disease Management
  • Minimizing Peanut Disease
  • Peanut RX
Weed Management
  • Weed Response to
    Herbicides Used In
    Peanuts - PPI / PRE / AC
  • Weed Response to
    Herbicides Used In
    Peanuts -Postemergence
  • Weed ID Guide
Editors Note
Market Watch
Tank Contamination
News Products
News Briefs
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Disease Management:
Peanut Rx

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  Disease Management
 

Minimizing Peanut Disease
Peanut RX

   

Many factors combine to influence the risk of losses to TSWV. Some factors are more important than others, but no single factor can be used as a reliable TSWV control measure. Research data and on-farm observations indicate that when combinations of factors are considered, an individual field’s risk of losses due to TSWV can be estimated.

There is no way to predict with total accuracy how much TSWV will occur in a given situation or how the disease will affect yield, but by identifying high-risk situations, growers can avoid those production practices that are conducive to major yield losses.

The University of Georgia Tomato Spotted Wilt Risk Index for Peanuts was developed as a tool for evaluation of risk associated with individual peanut production situations.

When high-risk situations are identified, growers should consider making modifications to their production plan (i.e. variety, planting date, seeding rate, etc.) to reduce their level of risk. Using preventative measures to reduce risk of TSWV losses is the only way to control the disease.

Risk levels are relative. If this index predicts a low level of risk, we would expect that field to be less likely to suffer major losses due to TSWV than a field that is rated with a higher level of risk. A low index value does not imply that a field is immune from TSWV losses. Losses due to TSWV vary from year to year.

Measuring Risk To Fungal Diseases

The index presented here is designed to help growers approximate the magnitude of the risk that they face from foliar and soilborne diseases in the coming season. More importantly, it should serve as an educational tool that allows the grower to predict the benefits of different management practices he makes in hopes of producing a better crop.

The risks associated with leaf spot, white mold and Rhizoctonia limb rot diseases are to be determined independently in the index system.

When weather conditions are favorable for fungal diseases, especially when rainfall is abundant, even fields at initial “low risk” to fungal diseases may become “high risk.” PG


For each of the following factors that can influence the incidence of TSWV or fungal disease, identify which option best describes the situation for an individual field. An option must be selected for each risk factor, unless the information is “unknown.” A score of “0” for any variable does not imply “no risk,” but that this practice does not increase the risk of disease as compared to the alternative. Add the index numbers associated with each choice to obtain an overall risk index value. Compare that number to the risk scale provided and identify the projected level of risk.

Crop rotation with non-legume crop

Years Between
Peanut Crop
Spotted Wilt
Points
Leaf Spot
Points
Soilborne Disease
Points
*All crops other than peanut are acceptable to reduce leaf spot. Cotton and grass crops will reduce the severity of white mold. Rhizoctonia limb rot can still be a significant problem, especially with cotton, under longer rotations and favorable conditions (heavy vine growth and irrigation/rainfall). Rotation with soybeans does not reduce the risk to CBR or root-knot nematodes and has minimal impact on risk to white mold or Rhizoctonia limb rot. Rotation with grass crops will decrease the potential risk of limb rot; tobacco and vegetables will not.
      White mold Limb rot
0 NA 25 25 20
1 NA 15 20 15
2 NA 10 10 10
3 or more NA 5 5 5

Tillage

Tillage Spotted Wilt
Points
Leaf Spot
Points
Soilborne Disease
Points
*For fungal diseases, this does not apply for reduced tillage situations where peanut is following peanut in a rotation sequence. Limb rot can exist on some types of crop debris and use the organic matter as a bridge to the next peanut crop. Funky or irregular leaf spot tends to be more severe in conservation tillage than in conventional, though this malady is not typically associated with yield losses.
      White mold Limb rot
conventional 15 10 0 0
reduced* 5 0 5 5

Field history

Previous disease problems in the field?* Spotted Wilt
Points
Leaf Spot
Points
Soilborne Disease
Points
*YES would be appropriate in fields where leaf spot and/or soilborne diseases were a problem in the field despite use of a good fungicide program.
      White mold Limb rot
NO NA 0 0 0
YES NA 10 15 10

Variety selection

Variety1 Spotted Wilt
Points
Leaf Spot
Points
Soilborne Disease
Points

*Data for these new varieties is limited, and risk ratings will undergo changes as needed in the future.

1Adequate research data is not available for all varieties with regards to all diseases. Additional varieties will be included as data to support
the assignment of an index value are available.

2High oleic variety.

3Varieties Georgia-02C, Georgia Greener and Bailey have increased resistance to Cylindrocladium black rot (CBR) than do other varieties commonly planted in Georgia.

4 The malady referred to as “funky” or “irregular” leaf spot tends to be more severe in Georgia-02C than in other varieties. Although this condition can look like early leaf spot (Cercospora arachidicola), the cause of “funky” leaf spot is unknown. Disease losses are not typically associated with funky leaf spot.

5Tifguard has excellent resistance to the peanut root-knot nematode.

      White mold
AT-2152 30 30 30
Georgia Green 30 20 25
Florida Fancy2 25 20 20
Georgia-09B2 20 25 25
FloRun 1072 20 25 20
Georgia Greener3 10 20 20
Georgia-02C2,3,4 15 20 10
Georgia-06G 10 20 20
Florida-072 10 20 15
Georgia-07W 10 20 15
Tifguard5 10 15 15
Bailey*3 10 15 10
Georganic 05 10 10

Irrigation

Does the field receive irrigation? Spotted Wilt
Points
Leaf Spot
Points
Soilborne Disease
Points
*Irrigation has a greater effect on Rhizoctonia limb rot than on white mold or CBR.
      White mold Limb rot
NO NA 0 0 0
YES NA 10 5* 10

Planting date

Peanuts are planted: Spotted Wilt
Points
Leaf Spot
Points
Soilborne Disease
Points
Planting may be delayed due to inclement weather. Earlier plantings have a small increased risk for white mold. Later plantings may have greater limb rot at season end because of cooler soils.
      White mold Limb rot
NO NA 0 0 0
Prior to May 1 30 0 10 0
May 1 to May 10 15 0 5 0
May 11-31 5 5 0 0
June 1 - June 10 10 10 0 5
After June 10 15 10 0 5

Row pattern

Peanuts are planted in: Spotted Wilt
Points
Leaf Spot
Points
Soilborne Disease
Points
Only plant in conditions conducive to rapid, uniform emergence, otherwise the result may be poor stands or delayed, staggered emergence, both of which contribute to increased spotted wilt. A twin row is considered to be one row for purposes of determining number of plants per foot of row. Closer-planted peanuts tend to have an increased risk to white mold. Point values in parantheses are for varieties with a risk to spotted wilt of more than 25 points.
      White mold Limb rot
Single rows 15 0 5 0
Twin rows 5 0 0 0

Plant population (final stand, not seeding rate)

Plant Stand Spotted Wilt
Points
Leaf Spot
Points
Soilborne Disease
Points
 
      White mold Limb rot
Less than 3 plants per foot 25 NA 0 NA
3 to 4 plants per foot (3) 10 (15) NA 0 (0) NA
More than 4 plants per foot 5 NA 5 NA

At-Plant insecticide

Insecticide Used Spotted Wilt
Points
Leaf Spot
Points
Soilborne Disease
Points
*An insecticide’s influence on the incidence of TSWV is only one factor among many to consider when making an insecticide selection. In a given field, nematode problems may overshadow spotted wilt concerns and decisions should be made accordingly.
      White mold Limb rot
None 15 NA NA NA
Other than Thimet 20G or Phorate 20G 15 NA NA NA
Thimet 20G, Phorate 20G 5 NA NA NA

Classic herbicide

Classic Herbicide Usage Spotted Wilt
Points
Leaf Spot
Points
Soilborne Disease
Points
 
      White mold Limb rot
Classic Applied 5 NA NA NA
No Classic Applied 0 NA NA NA

Calculate your risk

  Spotted Wilt Points Leaf Spot Points White Mold Points Limb Rot Points
Peanut Variety        
Planting Date        
Plant Populations        
At-Plant Insecticide        
Row Pattern        
Tillage        
Classic Herbicide        
Crop Rotation        
Field History        
Irrigation        
Your Total Index Value        

Interpreting Your Risk Total
Point total range for tomato spotted wilt = 35-155.
Point total range for leaf spot = 10-100.
Point total range for white mold = 10-95.
Point total range for Rhizoctonia limb rot = 15-75.

Risk

  Spotted Wilt Points Leaf Spot Points Soilborne Disease Points
High Risk Greater than or equal to 115 65-100 55-80 To be determined
High Risk for fungal diseases: Growers should always use full fungicide input program in a high-risk situation.
Medium Risk 70-110 40-60 30-50 To be determined
Medium Risk for fungal diseases: Growers can expect better performance from standard fungicide programs. Reduced fungicide programs in research studies have been successfully implemented when conditions are not favorable for disease spread.
Low Risk less than or equal to 65 10-35 10-25 To be determined
Low Risk for fungal diseases: These fields are likely to have the least impact from fungal disease. Growers have made the management decisions that offer maximum benefit in reducing the potential for severe disease; these fields are strong candidates for modified disease management programs that require a reduced number of fungicide applications.



Planting ‘Windows’ to Attain Low Risk for Spotted Wilt
If planting date were the only factor affecting spotted wilt severity, growers would have no flexibility in when they planted. Fortunately, other factors are involved and by choosing other low-risk options, growers can expand their planting date window. Remember, the goal is to have a total risk index value of 65 or less, regardless of which combination of production practices works best for you. The following table demonstrates how the planting date window expands as other risk factors go down. For example, where a grower achieves a good stand, uses strip tillage and twin rows, and Thimet, but does not use Classic, he may plant a “10” or “15” point variety at ANY time in the season and still be at “Low” risk for spotted wilt.

  Points assigned to the peanut variety of interest
  20 15 10
Production practices and final stand Planting date options to achieve a “low risk” for spotted wilt using above varieties
Poor stand, conventional tillage, single rows,
Temik, Classic is used
None None None
Average stand, twin rows, conventional tillage, May 11-25 May 11-June 5 May 1 - June
Good stand, strip tillage, twin rows, Thimet,
no use of Classic
After May 1 ANY ANY


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