Virginia Peanuts: Making Decisions for the 1st Leaf Spot Spray

    Peanut leaf spot.

    Right now most peanut growers are deciding when to apply the first leaf spot fungicide and which fungicide to use. The recommendation the past few years has been to start spraying peanut fungicides at R3 (beginning pod) but no later than July 10th.

    I recommend using a chlorothalonil product (Bravo, Echo, Equus and others) at the 1.5 pt/A rate. I also recommend using Alto at 5.5 fl oz/A + 1.0 pint/A of chlorothalonil as an alternative. Tebuconazole (Folicur) is often tank-mixed with chlorothalonil at 7.2 fl oz/A but I wouldn’t expect a lot of leaf spot activity with tebuconazole as resistance to that fungicide by the leaf spot pathogens is widespread.

    Tebuconazole may still provide some activity against southern stem rot (A.K.A. “white mold”). Subsequent fungicide applications for leaf spot can be made according to the last effective spray date (LESD) using the Virginia Leaf Spot Advisory on the Peanut-Cotton Infonet here or using a 14-day calendar-based approach.

    In some fields growers may see early spotting that could be from herbicide injury or irregular or “funky” leaf spot. Irregular leaf spot can look an awful lot like early leaf spot but generally occurs earlier in peanut development regardless whether environmental conditions are favorable or not for early leaf spot.

    According to the Virginia Leaf Spot Advisory the risk of developing leaf spot has been low to moderate across all location thus far, but with current rain conditions that may change. No known cause has been attributed for irregular leaf spot and it has not been shown to cause economic losses.

    My main concern is that irregular leaf spot may cause growers to react to what they think is the beginning of an early leaf spot epidemic and spray needlessly or use more expensive products to control leaf spot. With irregular leaf spot, brown spots may be surrounded by yellow halos or large yellowed areas, defoliation may or may not occur, and spores are never present on spots.

    Anytime you suspect irregular or actual fungal leaf spot you can bring or have samples sent to the Plant Diagnostic Clinic at the Tidewater AREC for identification. If you have question or concerns please don’t hesitate to contact me.

    David Langston, Plant Pathologist, Virginia Tech Tidewater AREC 6321 Holland Rd., Suffolk, VA 23437 cell phone (757) 870-8498 office phone (757) 807-6536 e-mail dblangston@vt.edu




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