Canopy hedge pruning in pecan production differentially affects groups of arthropod pests and associated natural enemies

Authors: TOLEDO, PEDRO - University Of Georgia; PHILLIPS, KATE - University Of Georgia; SCHMIDT, JASON - University Of Georgia; Bock, Clive; Wong, Colin; HUDSON, WILL - University Of Georgia; Shapiro Ilan, David; WELLS, LENNY - University Of Georgia; Acebes-Doria, Angelita

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2023
Publication Date: 11/11/2023
Citation: Toledo, P., Phillips, K., Schmidt, J., Bock, C.H., Wong, C.R., Hudson, W., Shapiro Ilan, D.I., Wells, L., Acebes-Doria, A.L. 2023. Canopy hedge pruning in pecan production differentially affects groups of arthropod pests and associated natural enemies. Crop Protection. 176. Article 106521. https://doi.org/10.1016/j.cropro.2023.106521.
DOI: https://doi.org/10.1016/j.cropro.2023.106521

Interpretive Summary: Pruning techniques in tree nut agroecosystems is crucial to achieving higher productivity and maintaining tree health. However, the implications of modifying canopy architecture on arthropod pest management are less explored. This two-year study investigated the implications of hedge-pruning pecan trees for critical arthropod pests and natural enemies by assessing: 1) the abundance and distribution (upper versus lower canopy) of leaf-dwelling aphids and mites; 2) presence of visually detectable injuries caused by black pecan aphids and Phylloxera spp, and 3) abundance of canopy-dwelling aphid parasitoids and parasitized hosts, 4) abundance of western predatory mites as well as 5) the presence and prevalence of entomopathogens that dwell in the pecan understory. Hedge-pruning decreased Phylloxera infestations but increased pest pressure from scorch mites and the yellow aphids. Differences in black pecan aphid populations did not differ between hedged and non-hedged trees in the first year, but damage was reduced in hedged trees. In the second year, hedging increased black aphid abundance but damage was not affected. Predatory mites were less abundant in hedged trees in the first year, but more mites were found in hedged trees in the second year, likely responding to prey location. Parasitoids and soil-borne entomopathogen activities were not affected by hedging. Overall, the effects of hedging were not consistent across pests and enemies. However, it is important to consider tree architecture and its implications into pest management strategies for perennial tree crops and other agroecosystems.

Technical Abstract: Controlling canopy growth and size through pruning techniques in perennial agroecosystems is often crucial to maximizing productivity. However, the implications of modifying canopy architecture for arthropod management are often overlooked. We studied the effects of hedge pruning on pests and natural enemies on mature pecan trees by assessing the abundance of: 1) leaf-dwelling aphids and mites, 2) visually detectable injuries caused by black pecan aphids [Melanocallis caryaefoliae (Davis)] and Phylloxera spp., 3) aphid parasitoids and parasitized hosts (aphid mummies), and 4) predatory mites. Additionally, we assessed the prevalence of entomopathogens that dwell on the orchard floor, under the trees. Hedge pruning decreased Phylloxera infestation but increased pressure from scorch mites and the yellow aphid complex. Black pecan aphid abundance responded inconsistently, but their damage was consistently reduced in hedged canopies. Predatory mites were only affected by hedging in the second year when higher populations were observed. Although parasitoid wasp abundance was not affected by hedging, more parasitized aphids (mummies) were observed in trees that did not receive pruning in the first year. Also, higher activity of entomopathogens was observed in soil cores collected under hedged trees in the first year but lower in the second. Taken together, the effects of hedge pruning pecan canopies were case-specific, and cannot be generalized across pests or natural enemies. Nevertheless, structural and environmental variation across seasons and within hedge pruning systems clearly have implications for crop protection in pecans and other perennial systems.