Peanut Disease Update

The risk of developing foliar diseases such as Early leaf spot increased in these two last weeks in Oklahoma, with the decrease in air temperatures (below 90° F) and relative humidity. It’s time for the growers to scout the fields and make decisions regarding the application of foliar fungicides. The first symptoms of Early leaf spot were observed on 07/19/2024 in the peanut research plots in Fort Cobb, Oklahoma. Although, at a low frequency, leaf spots could be observed in the upper and lower canopy of the peanut crop.

 

A decision support system (DSS) known as Leaf Spot Advisor is available for peanut growers and stakeholders to provide recommendations regarding the best moment for fungicide applications. The advisory calculates the number of hours that are conducive for the development of the disease. Spraying is recommended when 36 “leaf spot hours” have accumulated from either 30 days after planting or 10 days from the last fungicide application. The Leaf Spot Advisory system is currently running on the Mesonet webpage. To access the advisory on the Mesonet website, please follow the below:

 

1. Open the Mesonet webpage
   
   
   
   
2. Click on the Agriculture tab on the upper part of the page
   
   
   
   
   
3. After that, click on Crops on the lower left part of the page
   
   
   
   
   
4. Click on the peanut icon
   
   
   
   
   
5. Select the Leaf Spot Advisor
   
   
   
   
   
6. After that, you will have access to the features available in the Leaf Spot Advisor. Notice a PDF document on the left lower corner of the page explaining how to use the advisor.
   
   
   
   
   
7. For example, I selected the Mesonet site at Fort Cobb. The Product is the Spray Decision Advisor. My peanut field was planted on 05/14/2024, and the first fungicide application was on 07/09/2024. Click on Get Data.
   
   
   
   
8. According to the advisory, the decision is NOT to SPRAY. However, the next fungicide application will be needed soon, since 34 “leaf spot hours” already accumulated in the last 10 days from the first application of fungicides, and 36 “leaf spot hours” are necessary to recommend the next fungicide application
   

 

 

A) Peanut plants showing symptoms of Early leaf spot (Passalora arachidicola).

 

 

B) Early leaf spot causes brown to black lesions in the peanut leaves, that start circular as pinpoint-size dots and present a distinct yellow border or halo.