Many peanut growers have reached, or are rapidly approaching, the start of their peanut fungicide program.
Our early summer weather has been marked by warm temperatures coupled with scattered storms. These conditions are generally favorable for the development and spread of leaf spot, white mold, Rhizoctonia limb rot, and other diseases.
The current forecast is for an active hurricane season which could bring torrential rainfall and storms that would spread disease and affect growers’ abilities to effectively manage diseases.
The good news for growers today is that we have an abundance of effective fungicides that can be used to manage diseases in their peanut crop. We have never had a more effective arsenal to manage the many fungal diseases that affect the peanut crop.
Today, a difficulty for growers is how best to select a fungicide program that is both effective in the management of disease and cost effective.
Bob Kemerait, University of Georgia Extension pathologist, in the remainder of this article, has dissected an effective fungicide program into its basic components.
(1.) All peanut fungicide programs must successfully control foliar diseases, e.g. early leaf spot and late leaf spot, and soil borne diseases including Aspergillus crown rot (especially at the seedling stage), white mold and Rhizoctonia limb rot. Some growers may also need to control Cylindrocladium black rot (CBR) but I have yet to note CBR in Coffee County.
(2.) Triazole fungicides include tebuconazole, Tilt (propiconazole), Provost (tebuconazole plud prothioconazole), Proline (prothioconazole), Eminent (tetraconazole) and Quash (metconazole). Strobilurin fungicides include Abound (azoxystrobin), Headline (pyraclostrobin), and Evito (fluoxastrobin). Triazole/chlorothalonil combinations include Tilt/Bravo, Echo/PropiMax and Echo Eminent. Triazole/strobilurin combinations include Stratego and Absolute. Unique classes include chlorothalonil, Elast, thiophanate methyl (Topsin M) and flutolanil (Convoy).
(3.) Growers should consider initiating a fungicide program for control of leaf spot at approximately 30 days after planting (DAP). Growers may want to begin their program earlier if weather has been especially wet or if they have a poor rotation (peanuts behind peanuts).
Growers can delay a fungicide program if, using the 2010 Peanut Rx, their field is at reduced risk to leaf spot diseases or if they plan to use higher rates of Headline (9 fluid ounces per acre) or Tilt/Bravo (2.25 pints per acre).
(4.) There are a number of fungicides available for the control of leaf spot. These include:
(a.) Bravo WeatherStik, Echo, and other formulations of chlorothalonil. These are protectant fungicides and must be applied before disease becomes established in a field. Though chlorothalonil has been around for nearly 40 years, it still provides good disease control when used appropriately. Chlorothalonil, 1.5 pints per acre, is often used in fungicide applications at 30 and 44 days after planting. It is also frequently tank-mixed with a fungicide like tebuconazole (e.g. Folicur 3.6F, Tebuzol 3.6F, etc.) to enhance leaf spot control. Resistance management: Chlorothalonil can be used in any fungicide program and is an excellent partner for fungicide resistance management.
(b.) Elast. Elast (dodine) is another protectant fungicide used in peanut fungicide programs to manage leaf spot. Elast is best used earlier in the growing season where it competes well with chlorothalonil. Growers should avoid using Elast later in the growing season. Elast is applied at 15 fluid ounces per acre when used alone or at 12.7 fluid ounces per acre when tank-mixed with a fungicide such as tebuconazole.
As a protectant, Elast must be applied prior to onset of infection. Resistance management: Elast is a unique chemistry in our arsenal and can be used in programs with all other peanut fungicides without concern for resistance. When used only early in the season, is at low risk for development of fungicide resistance.
(c.) Tilt/Bravo. Tilt/Bravo is a pre-mix of propiconazole and chlorothalonil which combines a systemic fungicide and a protectant fungicide for management of leaf spot. The Tilt/Bravo pre-mix is typically applied at a rate of 1.5 pints per acre when used in applications 30 and 44 days after planting or 2.25 pints per acre when applied at 40 days after planting. When sold as a co-pack (as is the similar product Echo/PropiMax) Tilt/Bravo is applied at 2 fluid ounces per acre propiconazole and 1 pint per acre chlorothalonil.
Tilt/Bravo is best applied preventatively. However, the addition of Tilt does offer limited curative activity. Resistance management: Neither Tilt/Bravo nor Echo/PropiMax should be used in the same program with other triazole fungicides (to include tebuconazole, Quash, or Provost) or Artisan (flutolanil plus propiconazole) unless these fungicides are tank-mixed with a protectant fungicide like chlorothalonil.
(d.) Stratego. Stratego is a pre-mix of propiconazole and trifloxystrobin and is thus a member of both the triazole and strobilurin classes of fungicides. Stratego, applied at 7 fluid ounces per acre typically at 30 and 40 days after planting, offers a combination of systemic and protective activity.
Like Tilt/Bravo, Stratego offers limited curative activity but is most effective when applied preventatively. Resistance management: Because it is a pre-mix of a triazole and a strobilurin fungicide, we encourage growers to avoid using Stratego with other triazole or strobilurin fungicides.
(e.) Absolute. Absolute is a combination of tebuconazole and trifloxystrobin. Because there is confirmed resistance to tebuconazole in Georgia from leaf spot pathogens, it is difficult to find an appropriate fit for a product that is a combination of tebuconazole and trifloxystrobin. Absolute should be used with caution and not in programs that contain other triazole or strobilurin fungicides.
(f.) Echo/Eminent. Echo/Eminent is a new co-pack from Sipcam Agro that contains chlorothalonil (1 pint per acre) and tetraconazole (7.2 fluid ounces per acre). (Note — until this product is further tested, use rates may vary.) Echo/Eminent offers both protective and systemic modes of action and is typically applied at 30 and 44 days after planting.
In recent trials at UGA, this product has performed well. Resistance management: Echo/Eminent should not be used in the same program with other triazole fungicides (to include tebuconazole, Quash, or Provost) or Artisan (flutolanil plus propiconazole) unless these fungicides are tank-mixed with a protectant fungicide like chlorothalonil.
(g.) Headline. Headline (pyraclostrobin) is an excellent fungicide for management of leaf spot. Headline is applied at 6 fluid ounces per acre when used at 30 and 44 days after planting or at 9 fluid ounces per acrewhen applied as a single application at 40 days after planting.
Headline offers excellent protective control and some of our best curative control; though as with all fungicides, it is best used before disease is established in the field. Resistance management: Headline should not be used in the same programs with Abound, Evito, Stratego, or Absolute.
(h.) Topsin M. Topsin M is thiophanate methyl, a fungicide in the benzimidazole class. Though resistance exists to benzimidazole fungicides, which includes Topsin M, this fungicide can be effectively tank mixed (5 fluid ounces per acre) twice with a fungicide like tebuconazole.
Topsin M can also be used quite effectively as a final application at 10 fluid ounces per acre at the end of the season. Used appropriately, Topsin M can offer very good leaf spot control. We have not been able to determine any relationship between increased “peg strength” and use of Topsin M.
(5.) Initiation of a soilborne fungicide for the management of white mold and Rhizoctonia limb rot usually occurs approximately 60 days after planting. In some years, especially when soil temperatures are unusually high earlier in the season, growers may want to begin their soilborne program earlier.
High temperatures, especially when coupled with frequent rains, are a proven recipe for significant outbreaks of white mold. Fungicides applied for the control of soil borne diseases must also control leaf spot or must be tank-mixed with a fungicide that does control leaf spot (e.g. Convoy plus chlorothalonil).
(6.) Fungicides used to manage soilborne diseases include the following:
(a.) Tebuconazole, most famously known as Folicur 3.6F, is now sold under a number of names. Tebuconazole is typically applied in a four-block program beginning 60 days after planting at a rate of 7.2 fluid ounces per acre. Tebuconazole is typically tank-mixed with another fungicide, e.g. chlorothalonil at 1 pint per acre or Topsin M at 5 fluid ounces per acre, to improve control of leaf spot. Resistance management: Tebuconazole should not be used with other triazole fungicides.
(b.) Provost is a combination of tebuconazole and prothioconazole and offers excellent control of leaf spot diseases and white mold. It is also our most effective foliar-applied fungicide for management of CBR. Provost is applied in a four-block program beginning 60 days after planting at a rate of 8 to 10.7 fluid ounces per acre. The 8 fluid ounces rate is effective for “normal” threat from white mold and limb rot.
The 10.7 fluid ounce per acre rate is effective where white mold is more severe and where CBR is present. Resistance management: Provost should not be used in the same program with other triazole fungicides.
(c.) Quash is a new fungicide from Valent. Quash is metconazole and is applied in a four-block program beginning 60 days after planting at a rate ranging from 2.5 to 4 fluid ounces per acre. Though we continue to learn more about Quash, it appears that the 2.5 fluid ounces rate is appropriate where threat from white mold is not severe; where the threat is severe the rate should be increased to 4 fluid ounces per acre.
Where growers have experienced difficulty controlling leaf spot with tebuconazole, they should mix chlorothalonil, 1 pint per acre, with the Quash.
Resistance management: Quash should not be used in the same program with other triazole fungicides.
(d.) Abound (azoxystrobin) offers excellent control of Rhizoctonia limb rot and good control of white mold. Abound is typically applied at 60 and 90 days after planting at a rate of 18.5 fluid ounces per acre. Resistance management: Abound should not be used in the same program with Headline, Stratego, Evito or Absolute.
(e.) Evito (fluoxastrobin) is another strobilurin fungicide and is also applied at 60 and 90 days after planting at a rate of 5.7 fluid ounces per acre. Evito is not “generic Abound” and should not be used in the same program with Abound, Headline, Stratego or Absolute.
(f.) Headline (pyraclostrobin) can be used for the management of soilborne diseases when applied at a rate of 12 fluid ounces per acre, typically at 74 days after planting as a component of a traditional four-block program that would include a fungicide such as tebuconazole. Resistance management: Headline should not be used in the same program with Abound, Evito, Stratego or Absolute.
(g.) Artisan is a tank-mix of flutolanil and propiconazole. Artisan is excellent in the management of white mold. Artisan can either be applied at 60 and 90 days after planting at a rate of 26 to 32 fluid ounces per acre (in which case additional leaf spot control is generally not needed) or in a four-block program at a rate of 13 to 16 fluid ounces per acre (in which case a protectant fungicide like chlorothalonil, 1 pint per acre, should be mixed with each application). Resistance management: Artisan should not be used in the same program with other triazole fungicides unless all are mixed with a protectant fungicide like chlorothalonil.
(h.) Convoy is also an excellent product for the management of white mold. Convoy is not a pre-mix with propiconazole; Convoy must always be tan-mixed with a full rate of a leaf spot partner such as chlorothalonil at 1.5 pints per acre. Resistance management: Convoy can be used in a program with all other peanut fungicides.