Gibberellic acid decreases melanocallis caryaefoliae (hemiptera: aphididae) population density and chlorotic feeding injury to foliage in pecan orchards

Authors: Cottrell, Ted; WOODS, BRUCE - Retired ARS Employee

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2020
Publication Date: 11/5/2020
Citation: Cottrell, T.E., Woods, B.W. 2020. Gibberellic acid decreases melanocallis caryaefoliae (hemiptera: aphididae) population density and chlorotic feeding injury to foliage in pecan orchards. Pest Management Science. 77/1512-1519. https://doi.org/10.1002/ps.6173.
DOI: https://doi.org/10.1002/ps.6173

Interpretive Summary: The black pecan aphid is one of three aphid species attacking foliage of pecan trees. Feeding by the black pecan aphid triggers a physiological change within foliage mimicking natural leaf senescence and if aphid density is high, it can lead to defoliation. Application of gibberellic acid to pecan foliage mitigates black pecan aphid-elicited physiological disturbances. Gibberellic acid applied to orchard canopies was evaluated for efficacy regarding effects on black pecan aphid populations and possible negative side-effects on two natural enemy species and on return bloom of pecan trees. Gibberellic acid significantly reduced density of black pecan aphid nymphs but not adults. Percentage leaf chlorosis caused by the black pecan aphid was significantly reduced by gibberellic acid. Additionally, no negative side-effects of GA3 treatment were detected regarding population density of certain key natural enemy species or on return bloom of pecan trees. Timely foliar application of gibberellic acid to the orchard canopy protects foliage from senescence-like physiological responses triggered by the black pecan aphid. This reduces detrimental leaflet chlorosis, both senescence and abscission processes and horticulturally significant feeding injury. Additionally, the absence of apparent negative side-effects on key natural enemies and return bloom of pecan trees is suggestive of a practical means for efficacious non-insecticidal control of black pecan aphid populations in commercial orchards. This novel protective effect of gibberellic acid against aphid-elicited, senescence-like physiological responses may merit investigation as an IPM tool to manage aphid species eliciting similar senescence-like damage in other horticultural and agronomic crop species.

Technical Abstract: Melanocallis caryaefoliae (Davis) (Hemiptera: Aphididae), is one of three aphid species attacking pecan foliage (Carya illinoinensis [Wangenh.] K. Koch). Feeding by M. caryaefoliae triggers a physiological change within foliage mimicking natural leaf senescence; it can lead to defoliation. Pretreatment of pecan foliage with the phytohormone gibberellic acid (GA3) mitigates M. caryaefoliae-elicited physiological disturbances. GA3 application to orchard canopies was evaluated for efficacy regarding effects on M. caryaefoliae populations and possible negative side-effects on two natural enemy species and on return bloom of pecan trees. All GA3 treatment rate schedules significantly reduced population density of M. caryaefoliae nymphs but not adults or the two yellow aphid species attacking pecan. Percentage leaf chlorosis elicited by M. caryaefoliae was significantly reduced by tested rates of GA3 (i.e., 39.5 to 197.7 g a.i./ha). No negative side-effects of GA3 treatment were detected regarding population density of certain key natural enemy species or on return bloom of pecan trees. Timely exogenous application of GA3 to the orchard canopy protects foliage from senescence-like physiological responses triggered by M. caryaefoliae. This reduces detrimental leaflet chlorosis, both senescence and abscission processes and horticulturally significant feeding injury. Additionally, the absence of apparent negative side-effects on key natural enemies and return bloom of pecan trees is suggestive of a practical means for efficacious non-insecticidal control of M. caryaefoliae populations in commercial orchards. This novel protective effect of GA3 against aphid-elicited, senescence-like physiological responses may merit investigation as an IPM tool to manage aphid species eliciting similar senescence-like damage in other horticultural and agronomic crop species.