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Peanut Diseases/Fungicide Programs

Overview

A good fungicide program is one of the most important management practices involved in peanut production. In the southeast wet and humid conditions lead to many fungal diseases such as early / late leafspot and white mold (also known as stem rot). Fungicides for leaf spot diseases are often initiated around 30 days after planting, while fungicides that protect against soil borne diseases such as white mold are initiated around 60 days after planting. The length of time a fungicide can prevent plants from becoming infected by new fungal diseases is dependent on the fungicide and environmental conditions. Most fungal diseases are more problematic during wet conditions. Therefore, during high rainfall periods increased frequency of fungicide sprays may be required to protect the crop. During dry periods the interval of time between fungicide applications may be prolonged. Fungicides should be sprayed prior to the onset of disease! It is important for applicators to have good coverage of fungicide over crop. A spray volume of at least 10 gallons an acre is usually required.

Seedling Diseases

One of the best ways to manage seedling diseases is to plant into warm and moist soils. These conditions support germination, growth, and early season vigor helping to resist seedling diseases such as Aspergillus crown rot (in furrow fungicides such as Abound or Proline and seed treatments also help) and nematode damage. Planting into cooler and wetter soils slows the germination process giving seedling diseases more time to infect and kill seedlings.

Peanut rust

Peanut rust is a rare but explosive peanut foliar disease. Symptoms include orange pastules or dots appearing on the lower leaf surface. The pathogen is not believed to overwinter in north Florida and is likely blown in from Caribbean / south Florida. If rust is identified contact UF IFAS Columbia County extension and consider shortening spray intervals. Many of our fungicides sprayed for leaf spot and white mold have activity against rust such as chlorothalonil and tebuconazole products as well as brand names elatus / fontelus. Due to the sporadic nature of peanut rust, most fungicides have not been well tested in Florida on the disease.

Tomato Spotted Wilt Virus

Although not a fungal disease, tomato spotted wilt virus was problematic in 2019. Even though, it was a bigger problem in the pandhandle than the Suwannee Valley region. Infection of tomato spotted wilt virus is primarily caused by thrips. With the exception of thimet (phorate) insecticides aimed at reducing thrip populations have not been effective at suppressing tomato spotted wilt virus. It is unclear how thimet suppresses tomato spotted wilt virus. It may cause a defense response in the plant to occur which allows the plant to better resist the virus. Application of thimet in furrow at planting and avoiding the use of classic herbicide can help combat tomato spotted wilt virus. Later planted peanuts (mid may) are at less risk of thrip damage and tomato spotted wilt virus.

Additional information:

Use of velum total may help control nematodes in problematic fields and protect against leafspot diseases. If velum total is applied in furrow at planting leafspot fungicide programs may not need to begin until 45 days after planting rather than 30 days. Syngenta’s new leaf spot fungicide Miravis may allow for growers to switch from a 7 to 5 spray program. Miravis should be sprayed early to mid-season. It will not be helpful as a final spray if your field already has leaf spot!

Peanut Rx (see link below) is a great tool for evaluating your fungicide program based on your peanut variety, management practices, and field history. Use of the tool can help growers evaluate their risk of tomato spotted wilt virus, leaf spot diseases, and soil borne diseases.

Peanut Rx Calculator:

https://peanuts.caes.uga.edu/extension/peanut-rx.html

See information below on different fungicide programs from a trial conducted at UF IFAS North Florida Research and Education Center – Suwannee Valley in 2019!

Credit: Dr. Nicholas Dufault, UF Plant Pathology Department and Keith Wynn, UF IFAS Hamilton County Extension.

 

 

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