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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #391029

Research Project: Healthy, Sustainable Pecan Nut Production

Location: Fruit and Tree Nut Research

Title: Rates and formulations of phoshite fungicides for pecan scab

item BRENNEMAN, TIMOTHY - University Of Georgia
item Bock, Clive
item JOHNSON, WALKER - University Of Georgia

Submitted to: Pecan Grower
Publication Type: Trade Journal
Publication Acceptance Date: 12/6/2021
Publication Date: 2/1/2022
Citation: Brenneman, T.B., Bock, C.H., Johnson, W. 2022. Rates and formulations of phoshite fungicides for pecan scab. Pecan Grower. Vol 34:22-28.

Interpretive Summary:

Technical Abstract: Phosphites are used at high rates compared to other fungicides, but are generally economical to use. They are very safe to humans, both applicators and consumers, but they can cause crop injury under some conditions. They are highly systemic which allows them to move both up and down in the tissue of treated plants. They also act in part by stimulating the host defenses, but are protectant. Kphite is labeled at a high rate of 8 pints/acre while Phostrol is 5 pints/acre. We used 2, 4, 6 and 8 pints/acre) applied with a hand sprayer using 100 GPA spray volume equivalents on individual terminals. The test was repeated for three years (2019 – 2021) on 8 different trees of both Desirable and Wichita, with 9-10 sprays per year. Miravis Top at 13.7 oz/acre and a non-treated control were included as checks. Incidence and severity of both leaf and nut scab were evaluated, and phytotoxicity was rated as the % of visible injury on the treated leaves. On leaves control tended to be better on Desirable than on Wichita, and there was clearly more of a rate response of the phosphites on Wichita than on Desirable. Higher rates giving better control of leaf scab on Wichita, but the three lower rates of both phosphites gave similar control on Desirable. There was a clear rate response of nut scab control from phosphites on both cultivars, with little differentiation between the 4 and 6 pintt rates of phosphite. The low rate of 2 pint/acre was less effective on both cultivars, especially compared to the 8 pintt rate. Miravis Top provided the best control of nut scab. Degree of injury was related to the rate of phosphite used. It is emphasized that phosphites do not normally cause injury when applied via air-blast sprayer, especially with fewer applications used in an integrated program with other fungicides. The data indicate that higher rates of phosphite are particularly beneficial on more scab susceptible cultivars.