By Travis Faske, Associate Professor/Extension Plant Pathologist
A recent policy change by the European Union will affect the use of propiconazole and phosphorus acid/phosphite fungicides in peanut. This change is NOT based on fungicide safety concern as these fungicides remain labeled for use in the US, but rather in the sale of peanuts treated with these fungicides to the European Union. Of the fungicides used in Arkansas, these active ingredients are not as common as others so this change will not have a dramatic impact on peanut production or peanut disease management in the state. To continue the sale of American peanuts in Europe peanut, producers should be aware of the fungicides affected by this policy and what alternative fungicides are available to manage peanut diseases.
The European Union policy makers decided the methods used years ago to determine the maximum residue levels (MRL) for propiconazole was inappropriate and are not valid in today’s market. Based on a new procedure to measure propiconazole residue in treated peanuts, the MRL was set to very low. Therefore, in theory, using propiconazole at labeled rates might result in residue level above a very low MRL and result in the rejection of those peanut lots. Until data can be generated to raise the level set for propiconazole, peanut buying points are notifying growers to not apply any products containing this fungicide for the 2016 cropping season. Propiconazole is used to control leaf spot diseases in peanut and is sold as Bumber, Propimax, Tilt, and Topaz. Propiconazole is more commonly used as a premix fungicide in peanut. Some premix combinations include those mixed with chlorothalonil (Tilt/Bravo and Echo/PropiMax) trifloxystrobin (Stratego) and flutolanil (Artisan). Alternatives to Tilt/Bravo include; Bravo (1 pt/A) + Alto (5.5 oz/A), Bravo (1 pt/A) + Emeinent (7.2 fl oz/A) for leaf spot control. The active ingredient in Alto is cyproconazole and for Eminent, tetraconazole, which provide some systemic activity in leaf spot protection. Given that southern blight caused by Sclerotium rolfsii is a major issue in Arkansas a substitute for Artisan may be more important. Producers can continue to use flutolanil as Convoy (1 pt/A) to control southern blight and combine with Bravo (1 pt/A) for effective leaf spot control. Other alternative fungicide for southern blight and leaf spot control, and a list of products that contain propiconazole can be found in the MP 154.
Phosphite/phosphours acid-fungicides are used to manage Pythium pod rot. These fungicides are sold as solo products like K-Phite and Fosphite or mixed with tebuconazole and sold as Viathon. Phosphite fungicides are considered to be very safe and as of result, do not have an MRL set by the EPA. Because of the lack of an MRL, the European Union has set their limit to very low. Until data can be generated to raise the level set for phosphite fungicides, peanut buying points are notifying growers to not use these fungicides for the 2016 cropping season. Alternative fungicides include Ridomil Gold (mefenoxam) or Metastar (metalaxyl) for control of Pythium pod rot. Cultural practices to manage Pythium pod rot consist of selecting fields with good drainage, minimizing the duration of standing water in a furrow irrigated field, and crop rotation to reduce the amount of inoculum for the subsequent crop. Additionally, studies have shown that applying calcium as lime at flowering can reduce the severity of Pythium pod rot in peanut.