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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #342874
Title: Influence of fungicides on gas exchange of pecan foliage

Author
item Wood, Bruce
item Bock, Clive

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2017
Publication Date: 6/30/2017
Citation: Wood, B.W., Bock, C.H. 2017. Influence of fungicides on gas exchange of pecan foliage. Plant Pathology. 67(2):265-276. https://doi.org/10.1111/ppa.12753.
DOI: https://doi.org/10.1111/ppa.12753

Interpretive Summary: Several fungicide chemistries used for disease control on pecan, but there is little knowledge of side-effects of these chemistries on host physiology, including photosynthesis (Pn). This study quantifies the impact of several fungicides used to control scab on Pn and other gas exchange characteristics of pecan foliage. Multiple field experiments found that certain fungicide chemistries reduce Pn , stomatal conductance (Cs), transpiration rate (Tr) and water use efficiency (Ew; Pn/Tr) whereas others had no effect. Neither triphenyltin hydroxide nor the triazoles tested had a negative impact on gas exchange characteristics. However, dodine, phosphorous acid, ziram and certain strobilurins were capable of suppressing gas exchange, especially Pn, up to several weeks after a single treatment. Suppression of gas exchange by certain fungicides was relatively short term, but was long term or permanent for others. The results suggest that use of fungicides in commercial pecan orchards might result in negative side-effects which need to be taken into consideration in determining how to best utilize these fungicide tools in pecan disease management.

Technical Abstract: There are several fungicide chemistries used for disease control on pecan (Carya illinoinensis), but there is little or no knowledge of subtle short- or long-term side-effects of these chemistries on host physiological processes, including photosynthesis (Pn). This study quantifies the impact of several fungicides used to control scab on Pn and other gas exchange characteristics of pecan foliage and provides much-needed insight to ensure proper usage in commercial pecan operations. Multiple field experiments found that certain fungicide chemistries reduce Pn , stomatal conductance (Cs), transpiration rate (Tr) and water use efficiency (Ew; Pn/Tr) whereas others are benign. For example, neither triphenyltin hydroxide nor the triazoles tested had a negative impact on gas exchange characteristics regardless of when measurements were taken or the number of spray applications. However, dodine, phosphorous acid, ziram and certain strobilurins were capable of suppressing gas exchange, especially Pn, up to several weeks after a single treatment. Suppression of Pn by certain fungicides was relatively short term, but was long term or permanent for other fungicides. In certain cases, leaf Pn was suppressed by as much as 50-80% for at least several weeks after a single exposure. These studies suggest that use of fungicides in commercial pecan orchards might result in negative side-effects which need to be taken into consideration in determining how to best utilize these fungicide tools in pecan disease management.