Commodities: Fieldcrops: Peanuts: 2007 Peanut Update

2007 Peanut Disease Update

Bob Kemerait, Tim Brenneman, and Albert Culbreath

For most peanut growers in Georgia, the main focus of the 2006 season was on severe drought and not on disease management issues, with the exception of white mold that became problematic later in the season.

Despite predictions that spotted wilt would be severe in the 2006 season, based upon an assessment of weather conditions during the spring, this important disease was fairly mild for most growers in 2006. We estimate that losses to spotted wilt in 2006 were around 2.5%, which is one of the lowest loss estimates for this disease in years. It is not possible (or necessarily helpful) to predict the severity of spotted wilt in 2007. Growers are simply reminded that the best way to minimize their risk is to adhere as closely as possible to the guidance provided in the 2007 UGA Peanut Disease Risk Index, which is included in the Peanut Update.

White mold became a real problem for many peanut growers across Georgia in 2006. Despite dry conditions, the warm soils favored the development and spread of this disease. Also, many growers began to stretch the interval between fungicide applications due to the lack of rainfall. In delaying fungicide applications, some growers likely allowed the white mold epidemic to develop without proper control measures in place.

Peanut pod rot was an important problem for a number of growers last season, especially those in the eastern part of the state around Emanuel, Jefferson, and Burke Counties. The problem was most prevalent in dryland fields where growers had planted varieties with larger pods, such as AP-3. Despite apparently adequate levels of calcium in the soil, the dry conditions did not allow for sufficient uptake of calcium by the pods in some cases, thus resulting in severe pod rot. Despite the problems with varieties like AP-3, growers should recognize that this variety offers an EXCELLENT disease package, especially for spotted wilt and white mold. Although growers in dryland areas may be hesitant to grow this variety again, it has performed very well under irrigated conditions and with adequate rainfall.

Notes for 2007:

In addition to Vitavax PC and Dynasty PD, growers will now have the option of using Trilex Optimum (metalaxyl + carboxin + trifloxystrobin) or Trilex Star (metalaxyl + carboxin + trifloxystrobin + thiophanate methyl) as seed treatments. In studies conducted by Dr. Tim Brenneman, use of Vitavax PC, Dynasty PD, and Trilex Optimum have all performed very well in improving plant stand over seed that has not been treated with a fungicide. In the past, growers had to make a special request for seed to be treated with Dynasty PD. Now, the seed supplier will make the decision on weather to treat with Dynasty PD, Trilex Optimum, or Vitavax PC. In all probability, the use of Vitavax PC as a seed treatment for peanut will decline rapidly, though the product remains quite effective.

In 2007, growers will have access to a number of generic formulations of tebuconazole (the active ingredient in Folicur). Some of these include Tri$um (Cerexagri-Nisso), Integral (Luxembourg), Tebustar (Albaugh), Muscle and Muscle-Echo co-pack (Sipcam), Orius (MANA), and Tebuzol (UPI). These generic formulations of tebuconazole should be used like Folicur in a fungicide program. Theoretically, all of these tebuconazole formulations should perform like Folicur; however we at the University of Georgia have not tested each one of them in replicated fungicide trials. It is possible that some products are produced better than others and will thus perform better than others in the peanut field.

A new fungicide mix, Provost, from Bayer CropScience should be available to growers in the summer of 2007. Provost is a pre-mix of tebuconazole (Folicur) and prothioconazole (Proline). Provost should be labeled for use by peanut farmers throughout the entire 2007 season and will be used in a 4-block program like Folicur has been. From data collected at the University of Georgia, Provost offers excellent control of leaf spot diseases and control of white mold, Rhizoctonia limb rot, and CBR control that is at least as good as Folicur. The prothioconazole fungicide appears to have very good activity against CBR, especially when used in-furrow as Proline. Proline (prothioconazole alone) will likely be marketed as an in-furrow treatment beginning in 2008. The rate of application of Provost will vary somewhere between 8 and 10.5 fl oz/A depending on the severity of disease in a field.

All though there is growing evidence that leaf spot pathogens are becoming more resistant to tebuconazole, Folicur 3.6F performed well in 2006 in most situations for control of leaf spot and white mold. (NOTE: “more resistant” does NOT mean “completely resistant”.) Despite claims by some, Folicur remains an important fungicide for management of soilborne AND foliar diseases of peanut. HOWEVER, farmers are reminded that if they grow peanuts under conditions that favor leaf spot diseases, e.g. plant a more susceptible variety, have poor crop rotation, or have extended periods of wet weather, then they should consider taking additional steps for disease management. Tank-mixing Folicur (or other tebuconazole products) with a chlorothalonil product, e.g. 0.75 pt/A, or Topsin 4.5F (5 fl oz/A) will help to insure excellent leaf spot control. A co-pack of tebuconazole and chlorothalonil is being marketed by Sipcam as Muscle-Echo. Additional information on tank mixing tebuconazole with another leaf spot material appears later in this section.

Many growers used Artisan in 2006. Growers are reminded that if they choose to use less than 26 fl oz/A in an application, then they will need to tank-mix 1.0 pt/A of chlorothalonil with the Artisan to insure leaf spot control. Additionally, a new product, Trifecta, is being marketed that includes a co-pack of Artisan and chlorothalonil.

Evito 480SC is a new strobilurin fungicide (in the same class as Headline and Abound) that will be available for peanut growers in 2007. Evito is labeled to be used on peanut at 5.7 fl oz/A and on a similar 2-application timing to Abound (approximately 60 and 90 days after planting) for control of leaf spot and soilborne diseases. There is limited data from the University of Georgia on this product. Growers who wish to use Evito in 2007 are advised to do so cautiously (e.g. on limited acreage) until we have a better understanding of its performance in the field.

“Prescription fungicide programs” are defined as strategies designed to maximize yields and maintain disease control in a field using the appropriate number and type of fungicide applications based upon the risk to disease in the field. The goal of prescription fungicide programs is too use the right amount of fungicide for the level of disease expected in a field and to modify the fungicide use as the risk of disease increases or decreases as the season progresses.

Fields where the risk to disease is high, for example where fields have shorted crop rotation, are planted to less resistant varieties, and weather favors disease development should receive at least seven fungicide applications during the season, and perhaps more.

Fields where the risk to disease is reduced to a low or moderate level, for example where fields have longer rotations and are planted to more resistant varieties, typically do not need the same fungicide program as a higher risk field in order to maximize yields. Research data from many on-farm and small plot studies conducted at the University of Georgia have demonstrated that growers who manage their crop so as to reduce the risk to leaf spot, white mold, and Rhizoctonia limb rot can also reduce the number of fungicide applications and increase the value of their crop by cutting production costs. In low risk fields, it is quite possible to reduce the number of fungicide applications from seven to four, so long as the grower is willing to watch the field to insure that disease does not begin to develop unnoticed.

Growers interested in developing prescription programs should first assess the risk in their field(s) using the UGA Peanut Disease Risk Index and then contact their local county agent for guidance on a suitable fungicide program.

Crop Rotation

The practice of good crop rotation has always been at the foundation of optimum disease management in peanut, affecting not only nematodes and soilborne diseases, e.g. white mold, Rhizoctonia limb rot, and Cylindrocladium black rot, but leaf spot diseases as well. For this reason, Extension specialists at the University of Georgia stress the importance of avoiding planting peanuts in the same field more often than once every three years and rotating with a grass crop, e.g. bahiagrass or corn, if at all possible.

Growers planted peanut on approximately 750,000 acres in 2005. An important consideration for such an increase is that it is likely to reduce the time between consecutive peanut crops in many fields. This trend will increase the inoculum for nematodes and fungal diseases, making future disease control more difficult.

Since the recent change in the Peanut Farm Program, peanut farming in Georgia has expanded into “non-traditional” production areas in the southeastern portion of the state. Growers in this area frequently ask “Can I grow peanuts on my land in back-to-back seasons as I have not grown them here before?” The simple answer is, of course, you can plant peanuts on your land whenever you want to. However, even growers who are planting peanuts on “new peanut ground” should be discouraged from back-to-back peanuts if possible. Reasons for this include:

Many peanut growers around the state would love to have access to “new peanut ground” as populations of pathogens attacking the crop should be initially low. Therefore, it does not make much sense to lose this competitive edge in pursuit of the short-term goal of growing two or three crops of peanuts in succession.

Many new peanut growers are producing peanuts on land that has been cropped to cotton in recent years. Although cotton is not affected by the peanut root-knot nematode, early or late leaf spot, or Cylindrocladium black rot (CBR), and is only slightly affected by white mold, it is susceptible to diseases caused by Rhizoctonia solani. It is likely that despite previous cropping in a field, there will be significant populations of R. solani and perhaps smaller populations of Sclerotium rolfsii (white mold) in the field when peanuts are first planted. (This was observed in a test plot in Lanier County in 2004.) Without effective crop rotation, these populations may increase quickly.

In 2005, we observed an outbreak of CBR in a field in southeast Georgia planted for two consecutive years to peanut. Earlier cops of soybean had introduced this disease to the field and back-to-back years of peanut had intensified the problem.

One of the greatest benefits of crop rotation is that it increases the effectiveness of disease management programs. Effective crop rotation takes some of the “pressure off” of a fungicide program to minimize the impact of disease. Any fungicide program will be more effective where good crop rotation is practiced. In some situations, fields that are well rotated will require fewer, or at least less expensive, fungicide applications by the grower.

Recommendations from the University of Georgia for crop rotation and peanut production include the following:

Avoid planting peanut in the same field more than once out of every three years. Longer rotations, for example once every four years, are even better.

The best crops to rotate with peanut are grass crops, such as corn, sorghum, and bahiagrass. These crops will help to reduce the severity of diseases caused by Rhizoctonia solani, as well as CBR, white mold, and leaf spot diseases. Although corn and sorghum are alternate hosts for the peanut root-knot nematode, they are less affected than peanut is. Therefore, planting corn and sorghum should help to reduce populations of peanut root-knot nematode, though perhaps not as fast as when a non-host such as cotton is planted. Bahiagrass is susceptible to the lesion nematode, which can reduce the pod brightness important for the green peanut market.

Cotton is a very good rotation crop with peanut and should help to reduce the severity of white mold, leaf spot diseases, and CBR on future crops. Cotton is not a host for the peanut root-knot nematode, so this will be a beneficial effect as well. Cotton is a host for Rhizoctonia solani, so diseases caused by this pathogen will remain a concern in peanut-cotton rotations, especially in conservation tillage where crop debris remains on the surface.

Soybeans, other leguminous crops, and many vegetable crops are not preferred for rotation with peanut. Although such rotations are likely to reduce the severity of leaf spot diseases, they may not reduce the severity of white mold, Rhizoctonia limb rot, the peanut root-knot nematode, or, in the case of soybean, CBR.

2007 Peanut Disease Risk Index

The University of Georgia’s Peanut Disease Risk Index has been updated for 2007 and is included in this publication. Modifications to the spotted wilt portion were minimal and primarily related to information on varieties and on planting date. Adjustments to the fungal disease portion also focused on the information provided for many of the peanut varieties planted in Georgia.

DISEASE MANAGEMENT IN 2007

Tomato Spotted Wilt. Although tomato spotted wilt was less severe in 2006 than in the past few years, growers must remain vigilant in the management of spotted wilt and should use the Peanut Disease Risk Index as a guide for minimizing risk. Growers may also want to plant some of their acreage to some of the newer varieties that have resistance to spotted wilt that is greater than that of Georgia Green.

Every year growers are reminded that the goal of the Index is to minimize their risk point total for a specific field. The University of Georgia does not dictate when a grower must plant peanuts, for example in the middle of May. The purpose of the index is to allow growers to determine how to minimize their point totals given their own needs. For example, if a grower needs to plant in late April, he or she can still achieve a satisfactory point total by making adjustments to other parts of the index, such as selection of a more resistant variety.

Fungal Diseases. Good crop rotation remains the cornerstone of a good disease management program. We recommend that a grower plant peanuts in a field only once every three years, and once every four years is even better. Grass crops, such as bahiagrass and corn, are the best rotation crops with peanuts because they do not share the same diseases or pathogens. (Note: Bahiagrass is a host for the lesion nematode, which does affect peanuts, especially green peanut growers.)

Early and Late Leaf Spot Diseases. Both early and late leaf spot are commonly observed across Georgia’s peanut production region, though both diseases were affected by the dry weather conditions that occurred during the 2006 season. Growers can be sure that both leaf spot diseases will be potential threats in 2007.

Leaf spot control with tebuconazole. For the most part, use of tebuconazole provided acceptable control of leaf spot in 2006. Although tebuconazole was not as effective as other fungicides in the control of leaf spot in a number of fungicide trials, the differences were not large enough to be easily noticed by the grower. Folicur (and other tebuconazole fungicides) remains a very important component of our fungicide arsenal. Because the control of leaf spot is critical for optimal peanut production, growers who use Folicur or other tebuconazole products should consider the following guidelines.

Growers should wait 12-24 hours after applying Folicur before beginning to irrigate the field. Irrigation or rainfall within 12 hours of application will very likely reduce the effectiveness of leaf spot control.
If a significant rain event occurs within 12 hours of application of Folicur, the grower should consider retreating the field with a fungicide for leaf spot control ONLY (e.g. chlorothalonil) as soon as possible, hopefully within a couple of days. The grower should resume fungicide applications for control of soilborne diseases approximately 14 days after the last Folicur application.

Where conditions are unfavorable for development of leaf spot, e.g. good crop rotation and rainfall or irrigation is not excessive, growers should feel confident in using Folicur as they have in the past. It remains an excellent fungicide for management of soilborne diseases and has proven efficacy against foliar diseases. However, growers who use tebuconazole without a tank-mix partner should pay particular attention to disease control in their fields to insure that leaf spot does not develop.
If a grower finds conditions are favorable for leaf spot epidemics, e.g. excessive rainfall and/or poor crop rotation, then he should consider tank-mixing a reduced rate of a second fungicide for leaf spot control with 7.2 fl oz of tebuconazole. From studies in 2004, 2005, and 2006 good tank-mix partners with tebuconazole include chlorothalonil (0.75 pt/A or 0.7 lb/A) and Topsin 4.5F (5 fl oz/A with two of the tebuconazole applications). We do not recommend tank mixing a reduced rate of Stratego (propiconazole + trifloxystrobin) with tebuconazole as there have been questions on the effect of further reducing the rate of the strobilurin fungicide in this tank-mix. Tank-mixing Folicur with Prevam may also help to reduce the severity of leaf spot over Folicur alone.
Many growers have adopted the use of Headline in their fungicide program. Headline provides excellent control of leaf spot diseases and peanut rust and is also a strong component of a soilborne program. Using Headline in a Folicur/tebuconazole program should help to maintain satisfactory control of leaf spot in situations where this disease is likely to be severe.

Finally, tebuconazole and Folicur 3.6F remain important and effective weapons in the peanut growers’ arsenal of fungicides. Prudent growers will carefully consider the conditions at time of Folicur applications to determine what, if any, additional steps should be taken to insure satisfactory control.

Management Points for Leaf Spot

Practice good crop rotation.
Destroy any volunteer peanuts that may grow in a field and bury/remove old peanut hay that can serve as a source of spores for leaf spot diseases.
Do not delay the start of a leaf spot fungicide program.

When using chlorothalonil (e.g. Bravo Ultrex, Bravo WeatherStik, Echo, Equus, or other generics), Tilt/Bravo, Echo-PropiMax, Stratego, or Headline (at 6 fl oz/A), and you have adequate crop rotation, your first leaf spot spray will typically be applied somewhere between 30 and 35 days after planting.
In fields where risk to leaf spot has been calculated as low-to-moderate, we have maintained good control of leaf spot when using a single application of Tilt/Bravo 40 days after planting
Growers who use the AU-pnut forecasting system, automated at www.AWIS.com, can more effectively time their first application based upon environmental conditions.
If you are planting peanuts after peanuts, you will likely need to begin your leaf spot program earlier than 30 days after planting because of the increased risk of disease.
If you are using Headline (at 9 fl oz/A) for your first leaf spot spray, it is appropriate to combine your first two fungicide applications for leaf spot control (for example at 30 and 44 days after planting) into a single application of 9 oz of Headline at 38-40 days after planting.

Traditionally, fungicides are applied on a 14-day calendar schedule beginning after the first application. This 14-day interval may be modified for reasons such as those below:

The interval should be shorter than every 14-days if conditions:

Rainfall has been abundant and conditions are favorable for leaf spot.
You are using the AU-PNUT leaf spot advisory and it calls for an early application.
Peanuts follow peanuts in a field and leaf spot is expected to be severe.
Rainfall came on quickly after your last leaf spot spray and you are concerned that some of the fungicide may have been washed off the plants in the field too quickly.
You are planting a variety that has poor resistance to leaf spot diseases.
Peanut rust appears in your field prior to the end of the season.

It may be possible to extend the spray interval beyond 14-days if:

Conditions have been dry and unfavorable for leaf spot, especially if you use the AU-PNUT advisory for spray guidance.
You are using a variety with increased resistance to leaf spot, such as C99-R, Tifrunner, or GA-01R. For example, if pressure from soilborne diseases is not severe, the spray interval for C99-R could be every 21 days while it is possible to treat DP-1 only three times during the season. The real concern for these varieties is not leaf spot control, but control of Rhizoctonia limb rot. (Additional information can be obtained from your local Extension Agent).
You use the Peanut Disease Risk Index and find that the predicted risk of fungal disease in a field is low to moderate and rainfall has not been excessive since your last spray (additional information can be obtained from your local Extension Agent).
Since many fungicide applications are used to manage leaf spot diseases and soilborne diseases, one must consider the effect that an extended spray schedule would have on both types of disease (foliar and soilborne) BEFORE shifting from a 14-day schedule.

The “funky leaf spot”, whose cause is still unknown, typically affects peanut plants very early in the season and can look very much like early leaf spot. It may also cause considerable defoliation of early season foliage. Because this disease typically disappears by the middle of the season, it has not been found to be of real concern.
Current fungicides DO NOT control funky leaf spot; so do not be unduly alarmed by the appearance of leaf spots on your peanuts early in the season. Stay on a good fungicide program and have confidence that this program will control the important early and late leaf spot diseases.
Finding some leaf spot in a field at the end of the season is usually not a problem. As long the diseases are controlled throughout the season, limited defoliation (up to about 30-40%) is not likely to affect your yield. The appearance of leaf spot at the end of the season typically does not mean that your program was ineffective or a failure.
Some growers in Florida are mixing chlorothalonil with Topsin-M or Topsin 4.5F or copper fungicides such as Kocide for their final leaf spot sprays to increase peg strength prior to harvest. What do we recommend in Georgia?

Combinations of chlorothalonil and Topsin-M currently provide excellent control of leaf spot.
Combinations of chlorothalonil and copper are also effective in the control of leaf spot.
Data collected at Clemson University demonstrates that peg strength is not increased with use of Topsin-M, Topsin 4.5F, or copper (e.g. Kocide).

Failures in leaf spot management in a peanut field are often linked to:

Unacceptable delays in starting your program.
Improper calibration of equipment (not enough material was applied).
Unacceptable delays between applications, such as when weather conditions keep the grower out of the field.
Rain events immediately after a fungicide application have washed the fungicide away too quickly.

Use of Chlorothalonil.

Chlorothalonil is the active ingredient in Bravo products, Echo products, and a number of generics. It is quite effective in the management of leaf spot diseases. Key points:

All chlorothalonil products for peanut appear to be effective. Differences between one brand and another are related to the “stickers” and other substances that are added to the active ingredient to increase effectiveness.
There is no difference in efficacy between a flowable and dry-flowable formulation of chlorothalonil.
Two likely benefits from chlorothalonil products when compared to other products for leaf spot control are:

Price.
Use for fungicide resistance management.

The typical rate for a 720-F formulation is 1.5 pt/A; for a 90-DF formulation is 1.4 lb/A.
Chlorothalonil products are not systemic and must be applied to the leaf surface prior to infection by the fungus.
Generally, chlorothalonil products have been on the foliage long enough prior to a rain event IF they have had time to dry completely.
If you feel that your chlorothalonil application may not have had enough time to dry before rain, consider timing your next fungicide application a little earlier to compensate for any reduction in efficacy.
When conditions have been very favorable for leaf spot (a lot of rain), it is generally true that research plots treated with chlorothalonil will have more leaf spot at the end of the season than plots treated with a systemic fungicide for leaf spot control. This increase in leaf spot rarely results in a reduction in yield.
Tank mixing Topsin M with chlorothalonil provides a good option for growers who are looking for a “rescue treatment” when leaf spot is developing too quickly in their field.

Tilt/Bravo, Echo-PropiMax, and Stratego:

Propiconazole + chlorothalonil is marketed as two products, Tilt/Bravo and Echo-PropiMax.

The rate of this combination is 2.0 fl oz of propiconazole and 1.0 pt of chlorothalonil/A.
Tilt/Bravo is now marketed as a pre-mix which when applied at 1.5 pt/A, offers the same level of product as described above.
Tilt and PropiMax are systemic, which means that they can be absorbed into the leaf tissue offering some limited curative activity for recent infections.
Fungicide resistance management: improper use of Tilt/Bravo or EchoPropiMax with Folicur or Stratego may increase the risk of resistance to the sterol-inhibitor class of fungicides.

Propiconazole + trifloxystrobin is marketed as Stratego.

Stratego is also a systemic fungicide with limited curative activity.
For leaf spot control, Stratego is applied at a rate of 7.0 fl oz/A.
Fungicide resistance management: improper use of Stratego with Folicur, Tilt/Bravo, Echo-PropiMax, Abound or Headline will increase the risk of resistance to the sterol-inhibitor and strobilurin classes of fungicides.

Where do we see the best fit for these products?

Even though these fungicides have a systemic component, they should be applied BEFORE infection occurs in order to obtain maximum benefit.
When conditions for leaf spot are favorable, use of Tilt/Bravo, Echo-PropiMax, or Stratego often provides for better leaf spot control than with chlorothalonil alone.
If growers plan to use one of these fungicides, they are often used early in the season to help insure a good start to leaf spot management.
If conditions have been favorable for leaf spot (abundant rainfall), a grower has been delayed in spraying for leaf spot, or leaf spot is beginning to appear in the field, use of Tilt/Bravo, Echo-PropiMax, or Stratego may provide benefits beyond chlorothalonil.

Topsin-M (thiophanate methyl) is a fungicide in the benzimidazole class.

Topsin-M can be a very effective part of a leaf spot management program.
Growers who use a 4-block tebuconazole program can increase the control of leaf spot by tank-mixing 5.0 fl oz/A Topsin-M with 7.2 fl oz of tebuconazole in alternating applications (either 1 & 3 or 2 & 4).
Growers who are looking for an effective fungicide treatment, should leaf spot become a problem in a field, can make an application of Topsin-M (5.0-10.0 fl oz/A) tank-mixed with 1.5 pt/A chlorothalonil. This can be followed up with a second application of the same tank-mix or with an application of Tilt/Bravo.
Growers should make no more than two tank-mix applications of Topsin-M pert season in order to avoid fungicide resistance problems.

Pyraclostrobin is sold as Headline.

Headline has been the most effective fungicide labeled on peanut for management of leaf spot.
Headline has the best curative activity of any fungicide for control of leaf spot.
Fungicide resistance management: improper use of Headline with Abound, Evito, or Stratego will increase the risk of resistance to the strobilurin class of fungicides. In most cases, Headline should not be used in a fungicide program that contains Abound, Evito, or Stratego.
For leaf spot control, Headline is typically used as follows:

Two applications at 6.0 fl oz/A at approximately 30 and 44 days after planting. We generally do not spend much time with this pattern, as the one below is a much better option for the grower.
Combine two traditional leaf spot fungicide applications into a single application at 9.0 fl oz/A approximately 38-40 days after planting.
Note: Because of its power to control leaf spot, some growers have used Headline as a “salvage” treatment late in the season when leaf spot appears out-of-control in a field. Remember:

It would have been better to use the Headline earlier to try and avoid the problem entirely.
Headline may slow the epidemic of disease, but it will not cure the problem. You will still have leaf spot; perhaps not as much as you would have had if you had not treated with Headline.
Using a selective fungicide, such as Headline, when disease is present and severe will increase the risk for the development of fungicide resistance.

13. Although Folicur and Abound are typically thought of for control of soilborne diseases, they must also control leaf spot diseases as well. Problems associated with Folicur and leaf spot are usually traced back to rain or irrigation soon after application. To maximize leaf spot and white mold/limb rot control with Folicur, it is best that the crop dry for 24 hours before irrigation. Where rainfall is abundant, some growers will add a half-rate of chlorothalonil or Topsin to Folicur for added leaf spot protection.

Soilborne Diseases

White Mold and Rhizoctonia Limb Rot Diseases: White mold and Rhizoctonia limb rot are likely to occur in nearly every peanut field in Georgia. Losses caused by these diseases can be severe and they are much more difficult to control than leaf spot diseases. Prior to 1994 when Folicur was first labeled, growers did not have any truly effective fungicides to control theses diseases. Since 1994, growers now have six different fungicides from three different classes that can effectively control both white mold and Rhizoctonia limb rot. Still, white mold and limb rot remain troublesome to growers. Two of the reasons for difficulty in control are 1) it can be tough to tell when you need to begin spraying, and 2) it is not easy to get the fungicide to its target where it can affect the pathogen.

Management points for white mold and Rhizoctonia limb rot.

Practice good crop rotation.

Corn, grass crops, and bahiagrass are good rotation partners reducing effect of white mold and Rhizoctonia limb rot.
Cotton will reduce the risk of white mold but will have less benefit on Rhizoctonia limb rot.

Choose resistant varieties when available.

Some new varieties, such as C99-R, AP3, Georgia-02C, Georgia-03L and Georgia-01R, have increased resistance to white mold over Georgia Green.
Georgia Green appears to have better resistance to Rhizoctonia limb rot than many other varieties.

Use fungicides.

NOTE: No fungicide program will give the grower complete control of soilborne diseases in a field. We estimate that, at best, a good soilborne fungicide program will give 60-70% control under ideal conditions.
Initiating fungicide applications is often imprecise and is based upon experience.
The timing of fungicides for controlling white mold and limb rot must be early enough to protect the crop when the disease first appears. However, growers should avoid applying soilborne fungicides too early so that they will be available when needed later in the season.
Initial appearance of soilborne diseases is related to the soil temperature, the growth of the crop, and rainfall/irrigation.
In Georgia, we generally start spraying for soilborne diseases approximately 60 days after planting. At this time in the season, the growth of the crop and the environmental conditions are suitable for disease to occur. Because white mold and Rhizoctonia limb rot can occur earlier than this, the grower should watch his fields carefully to determine when the diseases appear.
Example: In 2003, rainfall was abundant and we predicted that severe white mold would occur early in the season. However, white mold did not appear until later in the season and was much of a late-season problem. The most probable reason for this was temperature. Although the moisture was suitable for white mold (and limb rot), the cooler-than-normal summer temperatures delayed the onset of white mold. In 2006, white mold was severe across much of the production region of Georgia despite dry conditions. Again, the warm soil temperatures resulted in outbreaks of white mold, though the drought reduced the severity of Rhizoctonia limb rot.
Fungicides are applied to the foliage, but must reach the crown and limbs of the plant in order to be effective against soilborne diseases.

The fungicides can be moved by rainfall and irrigation. If rainfall or irrigation occurs too quickly after application, the fungicide may not provide enough protection for leaf spot.
If the rainfall or irrigation is delayed, absorption of the fungicide into the foliage may reduce the amount available to fight soilborne disease.
In a dryland situation, lack of rainfall, and thus movement down the plant, will reduce the effectiveness of a soilborne fungicide. Still, the fungicide was probably not wasted; some of the product likely reached the desired target with the spray mix.

Management with tebuconazole.

Tebuconazole is marketed as Folicur, Tebuzol, Orius, Tri$um, Integral, Muscle, Tebustar, etc.
Tebuconazole is effective against white mold and Rhizoctonia limb rot.
Tebuconazole remains effective against early and late leaf spot; however the fungicide is not as effective as it once was.
It is recommended that tebuconazole remain on the leaf surface for 24 hours after application to insure enough is absorbed for leaf spot control.
If tebuconazole is washed from the leaves too quickly, leaf spot control may suffer, though the grower may get maximum control of white mold and limb rot.
In extremely wet weather, or when the threat from leaf spot diseases is elevated, growers may choose to mix 0.75 pt of chlorothalonil or 5 fl oz Topsin with 7.2 fl oz of tebuconazole to insure leaf spot control. However, the addition of chlorothalonil may impede the movement of Folicur from the foliage. Note: Topsin is added to two alternating applications of tebuconazole in a 4-block program.
Tank-mixing Folicur with the product Prevam has, in some trials, helped to reduce the severity of leaf spot over Folicur applied alone.
Tebuconazole is applied at a rate of 7.2 fl oz/A, beginning approximately 60 days after planting.
In the most traditional program, tebuconazole is applied in a four-block program, on a 14-day interval.
Fewer than four applications of tebuconazole may be sufficient in some low disease situations; however this will be an off-label program.
Improper use of tebuconazole with Stratego, Tilt/Bravo, or Echo-PropiMax could increase the risk of fungal resistance to the sterol-inhibitor fungicides.

Management with Provost (tebuconazole + prothioconazole)

Provost should be available to peanut growers in 2007 from Bayer CropScience.
Bayer CropScience will likely recommend that Provost be used in a 4-block program like Folicur.
Because Provost is a combination of two fungicides within the same chemical class (triazoles/DMI fungicides), it is EXTREMELY important that growers practice good fungicide resistance management principals with this product in order to maintain its efficacy over an extended period of time.
From University data, Provost has provided excellent control of leaf spot diseases and control of white mold, Rhizoctonia limb rot, and CBR that is at least as good as that of Folicur.

Management with azoxystrobin.

Azoxystrobin is marketed as Abound and is typically applied at 60 and 90 days after planting at 18.5 fl oz/A.
A lower rate (12.0 fl oz/A) is allowed by label in dryland situations; however it must be used with caution, as it will not have the “power” of the full rate. We typically do not recommend this rate unless each Abound application is alternated with applications of Folicur at 7.2 fl oz/.
Abound is effective against leaf spot diseases, white mold, and is excellent for management of Rhizoctonia limb rot.
For maximum efficacy against white mold and limb rot, the field should receive irrigation or rainfall within 72 hours after application.
Fungicide resistance management: To avoid problems with fungicide resistance, Abound should not be used in the same program with Evito, Absolute, Stratego or Headline.

Management with fluoxastrobin.

Fluoxastrobin is marketed as Evito 480SC.
Evito is in the same chemical class (strobilurins) as are Headline, Abound, Stratego, and Absolute and should not be used in the same fungicide programs as these products.
Recommended use for Evito is two applications of product (5.7 fl oz/A) timed approximately 60 and 90 days after planting.
We have limited research data on this product and growers should use it cautiously until its full potential is determined.
Evito is NOT “generic Abound”, despite some popular myth.

Management with flutolanil.

Flutolanil is an excellent fungicide for the management of white mold and is also effective against Rhizoctonia limb rot. It is not effective against leaf spot diseases.
Flutolanil is marketed as Moncut and Artisan.

Moncut 70 DF must be mixed with another fungicide for the control of leaf spot. Moncut 70 DF is typically applied at 1.07 lb/A, in the middle of the rate range.
Artisan is a combination of flutolanil and propiconazole. Therefore, it will control leaf spot, white mold, and limb rot. Artisan can be applied at a rate or 26 or 32 fl oz/A.
Moncut and Artisan are typically applied at 60 and 90 days after planting, though Artisan and Moncut can also be applied in a 4-block program.
When using Artisan in a 4-block program, it is applied at rates between 13 and 16 fl oz/A and tank-mixed with an additional leaf spot material, e.g. 1.0 pt chlorothalonil/A.
When using Moncut 70DF fungicide in a 4-block program, it is typically applied as 0.5 lb/A tank mixed with a FULL rate of some leaf spot material.
As a final note, the flutolanil products Artisan and Moncut performed exceptionally well in 2003 and 2006 large plot field trials where white mold was severe.

Management with pyraclostrobin.

Pyraclostrobin is sold as Headline (as discussed in the leaf spot section).
Headline is effective in a soilborne disease management program when applied at the 12 fl oz/A rate.
Headline is not used as a “stand-alone” soilborne fungicide, but rather is used in combination with tebuconazole, or perhaps Artisan or Moncut.
Headline is not used with Evito, Absolute, Stratego or Abound for fungicide resistance management concerns.
Use of Headline at 12.0 fl oz will provide adequate control of white mold and limb rot when used as a part of a soilborne program and will provide exceptional leaf spot control.
An ideal use of Headline would be 9 fl oz/A at 40 days after planting, 7.2 fl oz/A Folicur at 60 days after planting, and 12.0 fl oz/A Headline at 74 days after planting.

Management with mixed programs. Some peanut growers in Georgia are experimenting with fungicide programs that mix different fungicides for the control of soilborne diseases and the results can be outstanding. The goal in mixing fungicides is to capture the best control available through the use of multiple chemistries. While some of these programs, like the alternate use of Folicur and Abound, for a total of four soilborne fungicide applications, appear to be quite effective, the grower must accept all responsibility if his program is off-label.
Managing White Mold with Lorsban 15G. Prior to Folicur, the insecticide Lorsban 15G was one of the only chemicals that growers had to manage white mold. As Folicur and then Abound were labeled, growers turned away from Lorsban for control of white mold. However, results from field trials in 2003 demonstrate that application of Lorsban 15 G (13.6 lb/A) in conjunction with fungicides may provide control of white mold beyond that of the fungicides alone. It appears that Lorsban 15G may still have a place in white mold control.

Cylindrocladium Black Rot (CBR): CBR is a very challenging disease to control and of increasing importance to growers across the state. Crop rotation away from peanut and soybean is an important management tool. Also, it is important that growers not introduce infested soil from fields where CBR occurs to fields where it is not yet present. This can be done best by cleaning equipment and vehicles before traveling between fields. In recent years, it has been proven that CBR can be transmitted via seed, though at a very low rate. Growers should try to obtain seed produced in fields free of CBR. They should also recognize that much of the seed for Virginia varieties is produced in the Virginia-Carolina region where CBR is of even greater importance than it is in Georgia.

Management points for CBR

Crop rotation away from peanut and soybean. Unfortunately, once CBR is established in a field, it is very difficult to eliminate. Not only can the fungal pathogen survive for long periods of time in the soil, but it can also infect common weeds such as beggarweed and coffee weed.
Folicur and Abound are labeled for the “suppression” of CBR. This means that these fungicides may reduce the symptoms of disease and possibly increase yields above other fungicides. Growers who are battling CBR may choose to use Provost, Folicur, Abound, or Headline for CBR suppression, though results are variable and sometimes disappointing.
Varieties with some level of resistance were not available to growers until recently. In the past couple of years, two varieties, GA-02C and Carver, have been released and appear to have at lest some level of resistance to CBR. Growers who have fields where CBR is found may want to consider planting these varieties.
It has been found that CBR is more severe in fields where the peanut root-knot nematode also occurs. Therefore, growers who manage nematodes with either Telone II or Temik 15G may find some suppression of CBR as well.
Fumigation with metam sodium (e.g. Vapam) at 10 gal/A directly beneath the row 10 days prior to planting is currently our best management strategy for the control of CBR. Results can be quite dramatic and can allow growers to plant peanuts in fields where it would otherwise be nearly impossible to grow a crop.

Managing Seedling Diseases: Seedling diseases were typically not a concern for peanut growers in Georgia prior to the arrival of the tomato spotted wilt virus. Even if some plants were lost in a stand, the neighboring peanut plants were often able to compensate for the loss by growing into the vacated space. However, it is clear that spotted wilt can be devastating when fields have poor stands. For this reason, getting a good stand has become critical for growers. Below are some management techniques to reduce seedling diseases (primarily caused by Rhizoctonia solani and Aspergillus niger).

Rotate peanuts with grass crops to reduce the populations of Rhizoctonia solani.
Plant the peanut crop when soil temperatures are warm enough to produce rapid, vigorous germination and growth. This can help protect the plants from disease. Excessive moisture at planting will also increase the risk of seedling diseases.
Use quality seed that has a good germination rating and will grow vigorously.
Choose varieties that are known to germinate and emerge uniformly and with vigor.
Use only seed treated with a commercial fungicide seed treatment. The seed treatments that are put on commercial seed prior to purchase are outstanding and provide protection for the seed and seedling. Seed treatments include:

Vitavax PC
Dynasty PD (azoxystrobin + mefenoxam + fludioxonil)
Trilex Optimum (trifloxystrobin + metalaxyl + carboxin)
Trilex Star (trifloxystrobin + metalaxyl + carboxin + thiophanate methyl)

Use an in-furrow fungicide where the risk of seedling disease is great or where the grower wants increased insurance of a good stand.

Abound at 6.0 fl oz/A in the furrow at planting can provide increased control of seedling diseases, including Aspergillus crown rot.
Terraclor (64 fl oz/A) also provides additional control of seedling diseases when applied in-furrow.
Growers who are most likely to yield benefits from these in-furrow fungicides are those that have poor crop rotation and a history of seedling disease in the field.

Managing root-knot nematodes: Peanut root-knot nematodes are a severe problem in some fields in Georgia, especially in the sandy soils in the southwest corner of the state. Growers initially become aware of the problem when they note stunted plants across patches in their field. At harvest, many of the pods and pegs from these fields are galled and of poor quality. Based upon conversations with growers, it is likely that many fields across the state have problems with root-knot nematodes, but growers may fail to attribute the cause to nematodes. Below are some management options.

Use crop rotation to avoid building large populations of nematodes in a field. Cotton is an excellent rotation crop with peanut to reduce levels of nematodes.
Treat the field with Temik 15G. From our trials, Temik at 10-lb/A in-furrow followed by 10 lb/A at pegging provides good control. It appears that the 10-lb/A application at pegging-time is critical. Note: growers must not apply Temik to the crop any later than 90 days before harvest.
Telone II at a broadcast rate of 6 gal/A or an in-furrow rate of 4 gal/A can provide control of the root-knot nematodes as well on peanuts. The Telone must be applied 7-14 days before planting to avoid damaging the crop. Applications of Temik 15g at 10 lb/A at pegging may still be advisable, even when Telone II was used at planting.

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