Warm-Season Cover Crops for Pecan Orchards: Horticultural and Entomological Implications

Publisher Website
Google Scholar
Abstract
In an experimental grove of pecan (Carya illinoinensis [Wangenheim] K. Koch [Juglandaceae]), we surveyed potential “insectary crops” that might provide aphidophagous insects and other entomophaga with alternate foods, and thereby enhance biological pest control. Thirteen prospective warm-season cover crops were evaluated for associated aphids and entomophagous insects; an additional 11 crops or mixtures were considered in unreplicated plots. Seven crops developed adequate stands in the replicated study: sericea lespedeza (Lespedeza cuneate [Dumont] G. Don, cultivar ‘Lowtan’, Fabaceae), American jointvetch (Aeschynomene americana L., Fabaceae), sesbania (Sesbania exaltata [Rafinesque-Schmaltz] Cory, Fabaceae), cowpea (Vigna unguiculata ssp. unguiculata [L.] Walpers, no named cultivar, but termed “combine” or “reseeding” cowpea, Fabaceae), alyceclover (Alysicarpus vaginalis[L.] De Candolle, Fabaceae), a sorghum X Sudan grass hybrid (Sorghum bicolor [L.] Moench cultivar ‘Kow Kandy’, Poaceae), and buckwheat (Fagopyrum esculentum Moench, Polygonaceae). Together with late-seeded sunflower (Helianthus annuus L., cultivar ‘Triumph 565’), these were assessed weekly for crop- plant density, vegetational cover, and height; vegetational cover by weeds; and densities of insects. All crops except sorghum showed substantial declines in density through time, due to drought, pathogens, nematodes, shade, or a combination of these factors. Sesbania and buckwheat were the only crops that exhibited substantial declines in vegetational cover, whereas alyceclover showed a substantive increase. Sorghum attained the greatest mean height, followed by sesbania, alyceclover, sunflower, American jointvetch, cowpea, buckwheat, and lespedeza. American jointvetch, cowpea, sesbania, and hairy indigo all supported cowpea aphid (Aphis craccivora Koch), whereas sorghum hosted corn leaf aphid (Rhopalosiphum maidis [Fitch]) and greenbug (Schizaphis graminum [Rondani]). Aphidophaga observed included syrphid flies (e.g., Allograpta obliqua [Say], Ocyptamus fuscipennis [Say], Ocyptamus costatus [Say], Pseudodoros clavatus [Fabricius], Toxomerus boscii Macquart, and Toxomerus marginatus [Say]), and coccinellid beetles (e.g., convergent lady beetle [Hippodamia convergens Guerin-Meneville], seven-spotted lady beetle [Coccinella septempunctata {L.}, Cycloneda undet. sp. prob, sanguinea sanguinea [L.], and Olla v-nigrum [Mulsant], as well as various Scymninae). Entomophagous wasps observed included various Scoliidae, Sphecidae, Eumenidae, and Vespidae. Sesbania appeared the best source of cowpea aphid, and reservoir for pooled aphidophaga, including coccinellid beetles and syrphid flies. It also harbored relatively-low densities of red imported fire ant, which is believed to interfere with aphidophagous insects. Flowering buckwheat was attractive both to syrphid flies and predatory wasps. Showy partridge pea (Cassia fasciculata Michaux) and hairy indigo (Indigofera hirsuta L.), though not included in the weekly sampling, appeared promising. The former provided extrafloral nectar to various entomophagous wasps, whereas the latter hosted cowpea aphid which in turn attracted various aphidophaga after pecan leaves had fallen. We are conducting additional survey studies; also, critical experiments are underway in commercial pecan groves, to determine effects of understory cover crops on pest and beneficial insects.