Black pecan aphid (Hemiptera: Aphididae) management on pecan when gibberellic acid is applied concurrently with broad-spectrum insecticides

Authors: Cottrell, Ted

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2022
Publication Date: 3/4/2022
Citation: Cottrell, T.E. 2022. Black pecan aphid (Hemiptera: Aphididae) management on pecan when gibberellic acid is applied concurrently with broad-spectrum insecticides. Journal of Economic Entomology. 115(2):611-617. https://doi.org/10.1093/jee/toac009.
DOI: https://doi.org/10.1093/jee/toac009

Interpretive Summary: Pecan foliage is attacked by three aphid species: black pecan aphid, blackmargined aphid and yellow pecan aphid. Black pecan aphid feeding results in chlorotic zones surrounding the feeding site. Feeding by the blackmargined aphid and yellow pecan aphid does not. Application of gibberellic acid (GA3) to pecan foliage results in fewer black pecan aphid nymphs and less chlorotic injury. GA3 has potential to manage black pecan aphid later in the season when broad spectrum insecticides are used to control direct pests of pecan nuts but inadvertently induce aphid outbreaks. In this study, broad spectrum insecticides were used with GA3 or aphid insecticides in orchard trials during 2016 and 2017. Populations of aphids and natural enemies along with chlorotic feeding injury were assessed. When used concurrently with GA3 or aphid insecticides, broad spectrum insecticides did not flare black pecan aphid populations. However, the combined population of blackmargined aphids and yellow pecan aphids was higher in treatments with GA3 than with an aphid insecticide or the in the control treatment during one of two years. More often than not, GA3 and the aphid insecticide resulted in less chlorotic injury than observed in the control. Surprisingly, natural enemies were not significantly affected by broad spectrum insecticides applied concurrently with GA3. These results show that GA3 can be used to protect foliage from localized leaf chlorosis caused by the black pecan aphid.

Technical Abstract: Pecan foliage (Carya illinoinensis [Wangenh.] K. Koch) is attacked by three aphid species: black pecan aphid, Melanocallis caryaefoliae (Davis), blackmargined aphid, Monellia caryella (Fitch), and yellow pecan aphid, Monelliopsis pecanis Bissell, (Hemiptera: Aphididae). Black pecan aphid feeding causes a localized physiological change in foliage resulting in chlorotic zones surrounding the feeding site. Feeding by the blackmargined aphid and yellow pecan aphid does not. Application of gibberellic acid (GA3) to pecan foliage mitigates this physiological disturbance leading to fewer black pecan aphid nymphs and less chlorotic injury. GA3 has potential to manage black pecan aphid later in the season when broad spectrum insecticides are used to control direct pests of pecan nuts but inadvertently induce aphid outbreaks. In this study, broad spectrum insecticides were used with GA3 or aphicides in orchard trials during 2016 and 2017. Populations of aphids and natural enemies along with chlorotic feeding injury were assessed. When used concurrently with GA3 or aphicides, broad spectrum insecticides did not flare black pecan aphid populations. However, the combined population of blackmargined aphids and yellow pecan aphids was higher in treatments with GA3 than with an aphicide or the in the control treatment during one of two years. More often than not, GA3 and the aphicide resulted in significantly less chlorotic injury than observed in the control. Surprisingly, natural enemies were not significantly affected by broad spectrum insecticides applied concurrently with GA3. These results show that GA3 can be used to protect foliage from localized leaf chlorosis elicited by the black pecan aphid.