Application of plant growth regulators mitigates chlorotic foliar injury by the black pecan aphid (Hemiptera: Aphididae).

BACKGROUND: Black pecan aphid, Melanocallis caryaefoliae (Davis) (Hemiptera: Aphididae), feeding elicits localized chlorotic injury to pecan foliage [Carya illinoinensis (Wangenh.) K Koch] and apparent acceleration of leaf senescence and defoliation. The ability of certain plant growth regulators (PGRs) (forchlorfenuron, gibberellic acid and aviglycine) to prevent M. caryaefoliae from triggering pecan leaf chlorosis and senescence-like processes was evaluated on two dates in both 2006 and 2007. Treatments were applied to orchard foliage and used in laboratory leaf-disc bioassays to assess possible reduction in aphid-elicited chlorosis and concomitant effects on aphid mortality and development. RESULTS: Foliage pretreated with forchlorfenuron + gibberellic acid prior to being challenged with aphids resulted in significantly less aphid-elicited chlorosis than did control or aviglycine-treated leaf discs. No PGR affected aphid mortality; however, development time was increased by forchlorfenuron + gibberellic acid in 2006 and by aviglycine + gibberellic acid on one date in 2007. CONCLUSION: Certain PGRs possess the potential for usage on pecan to protect foliar canopies from M. caryaefoliae via changes in the susceptibility of the host leaf to senescence-like factors being introduced by feeding aphids. This protective effect on host foliage and the associated suppressive effect on development of feeding aphids might also be relevant to pest management programs on other aphid-crop systems in which aphid-elicited chlorosis and senescence-like processes can limit profitability.