Disease Updates and Links to Photos

— Written By

The photos Barbara has are excellent!

From Barbara Shew
Most growers should have applied the first leaf spot spray in early-mid July (R3). A second spray has not been recommended in most locations due to high temperatures, low rainfall, and until recently, low humidity. Application of foliar fungicides, especially chlorothalonil (Bravo and other brands), during hot dry spells can greatly increase the risk of spider mite problems. Using the advisory will help to minimize excess sprays during dry weather.

Over the weekend, many locations received rain and/or had periods of high humidity. Conditions at your location *may* become more favorable for leaf spot and a second spray advised for some locations within the next week or so.

Typically, mid-July to mid-August is the critical period for stem rot control. Growers should consider using a leaf spot fungicide that will also control southern stem rot for the next spray. These include Abound, Headline, and Provost. Convoy and tebuconazole are effective against stem rot but must be mixed with a fungicide that controls leaf spots. Until we see a general break in the heat and drought, I do not recommend that you apply chlorothalonil alone or in mixture with another fungicide. If you are using Convoy or tebuconazole, 6-9 oz of Headline would be a good alternative to chlorothalonil.
However, you should not make more than two applications of a group 11 fungicide (Headline, Abound, or Evito) per season. See the North Carolina Agricultural Chemicals Manual http://ipm.ncsu.edu/agchem/agchem.html or 2011 Peanut Information
http://ipm.ncsu.edu/Production_Guides/Peanuts/main.pdf for rates and additional details.

The hot, dry weather also has not favored Sclerotinia blight, but outbreaks may occur in irrigated fields or locations that receive ran. Rain (or irrigation) is an important risk factor for Sclerotinia blight. Keep in mind that your risk of Sclerotinia blight may be higher than advised at the nearest weather station if you irrigate or have had a local rainstorm. Fields with a history of Sclerotinia blight should be scouted carefully starting in early July. Make the first Sclerotinia fungicide application according to advisory or sooner if disease is observed.

Photos and detailed descriptions of peanut diseases can be found at http://www.peanut.ncsu.edu/ Disease advisories are posted daily at http://ncsupeanut.blogspot.com/

Article first appeared as North Carolina Peanut Note (PNNC-2011-025)