Minimizing Peanut Disease

Developed by The University of Georgia, College of Agricultural and Environmental Sciences; The University of Florida, Institute of Food and Agricultural Sciences; Auburn University, College of Agriculture

Many factors combine to influence the risk of losses to Tomato Spotted Wilt Virus. 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 Peanut Disease Risk Index, known as Peanut Rx, was developed as a tool to evaluate risk associated with individual peanut production situations.

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


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Risk levels are relative. If this index predicts a low level of risk, you could 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. However, a low index value does not imply that a field is immune from TSWV losses and losses due to TSWV vary from year to year.

For each of the following factors that can influence the incidence of TSWV or fungal disease, identify the option that 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 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.

 

pg 18 crop rotation

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.

pg 18 tillage

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.

pg 18 field history

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.

pg 19 variety selection

1 Adequate 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 is available. 2 High oleic variety. 3 Varieties 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. 5 Tifguard has excellent resistance to the peanut root-knot nematode.

pg 19 irrigation

Irrigation has a greater effect on Rhizoctonia limb rot than on white mold or CBR.

 

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.

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.

 

pg 19 row pattern

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 parentheses are for varieties with a risk to spotted wilt of more than 25 points.

 

 

 

pg 19 plant population

1 For varieties with a risk to TSWV of more than 25 points. 2 For varieties with a risk to TSWV of less than 25 points.

pg 19 at-plant insecticide

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.

pg 20 -1

 

 

pg 20 - 2

 

 

 

 

pg 20 - 3Planting ‘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.

pg 20 - 4