Evaluation of Botanical Oil Formulations for Management of Powdery Mildew and Mites

Experiments were conducted to evaluate the effects of newly created soybean oil formulations on powdery mildew (Erysiphe pulphra ), photosynthesis, phytotoxicity, and broad mites (Polyphagotarsonemus latus (Banks)) on dogwood ( Cornus florida (L.) 'Cloud Nine') trees, and to evaluate the amounts of formulations that are deposited and washed off of peach (Prunus persica, (L.)) leaves, dormant oak (Quercus phellos, (L.) ), and viburnum ( Viburnum x juddii) twigs after simulated rainfall. Oil treatments were applied using a back pack mist blower sprayed pre- and post- inoculation of powdery mildew to evaluate powdery mildew, photosynthesis, and phytotoxicity. Oil treatments were also applied to the dogwood trees after infestation of broad mites. Powdery mildew and phytotoxicity were rating using an eight and five-point rating scale, respectively. Photosynthesis was measured using an ADC-3 model portable infrared gas analyzer. Trees and shrubs were arranged in randomized complete block designs around a 2.7 (9 ft) high spray nozzle in order to evaluate the effects different soybean oil formulations had on oil deposited on leaves and dormant twigs and amounts washed off by simulated rainfall. The amounts of oil present on the leaves and twigs after spraying and simulated rainfall were determined by chloroform extraction. In both pre- and post-inoculation evaluations of oil formulations, less powdery mildew was present on the oil treated leaves than the water treated leaves. Sprays of oil formulations caused some yellowing on the foliage whether sprayed pre- or post-inoculation. None of the oil formulations significantly controlled broad mites. Oil formulations differed in the amount of oil residue left on the leaves and dormant twigs before and after different simulated rainfall amounts.