Fruit & Nut Research and Information Center
Fruit & Nut Research and Information Center
Fruit & Nut Research and Information Center
University of California
Fruit & Nut Research and Information Center

Walnut Insect, Mite & Nematode Pests

Walnuts in California > Deficiencies & Pests >  Insect, Mite & Nematode Pests

The prevalence of insect, mite and nematode pests varies from orchard to orchard and is influenced by geographic location, weather and orchard management practices. The following are widespread, common pests that can be problems throughout the walnut growing regions in California.

Soil borne parasitic nematodes damage the tree by feeding on the roots. Trees with high populations of nematodes may show stunted growth, low yields and water-uptake related problems. Because nematodes may be present in the soil prior to planting, it is advisable to investigate the previous planting history at each location and test the soil. Three groups of parasitic nematode are common in California; lesion nematode (Pratylenchus vulnus), ring nematode (Mesocriconema xenoplax), and root knot nematode (Meliodogyne) (UC IPM website, 2012). Lesion and ring nematodes cause the greatest damage to walnut production (Westerdahl et al 2003).

The most common and persistent insects that damage nuts are the codling moth (Cydia pomonella) and the walnut husk fly (Rhagoletis completa). A secondary pest is the navel orangeworm (Amyelois transitella). The impact of each of these pests on production varies among walnut cultivars. For example, cultivars that bear fruit mid to late season will be less affected by codling moth damage, although they will be more susceptible to walnut husk fly (Van Steenwyk and Barnett 1998).

Other minor walnut pests vary among regions in California, and include walnut and dusky-veined aphids (Chromaphis juglandicola and Callaphis juglandis), European red mites (Panonychus ulmi), red humped caterpillar (Schizura concinna), walnut scale (Quadraspidiotus juglansregiae), San Jose scale (Quadraspidiotus perniciosus), and frosted scale (Parthenolecanium pruinosum) (Van Steenwyk and Barnett 1998). These pests impact tree health by feeding on the leaves directly or sucking sap from the leaves and wood.

UC Statewide IPM Program: How to Manage Pests: Walnut

Photo Gallery

These photos of some of the major pests are accessed from the UC ANR Repository, are available courtesy of University of California research and extension personnel and programs, including the UC Statewide IPM Program. Photo information, including the photographer, is displayed when the larger image is viewed.

 Deficiencies | Insects, Mite & Nematode Pests | Diseases | Vertebrates

Codling moth larvae infesting walnut. Photo by Kathy Keatley Garvey
Codling moth larvae infesting walnut. Photo by Kathy Keatley Garvey
Crop damaged by codling moth. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Crop damaged by codling moth. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Walnut Husk Fly. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Walnut Husk Fly. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Husk Fly Maggot Damage. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Husk Fly Maggot Damage. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Navel orangeworm leaves copious webbing and frass in nuts it infests. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Navel orangeworm leaves copious webbing and frass in nuts it infests. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Dusky-Veined Aphids. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Dusky-Veined Aphids. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Adult European red mite. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Adult European red mite. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Mature Redhumped Caterpillar Larvae. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Mature Redhumped Caterpillar Larvae. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
San Jose scale and the covering of a mature female with a parasite exit hole. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
San Jose scale and the covering of a mature female with a parasite exit hole. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Walnut twig infested with walnut scale, Diaspidiotus juglans-regiae. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents
Walnut twig infested with walnut scale, Diaspidiotus juglans-regiae. photo by Jack Kelly Clark. UC Statewide IPM Project, © UC Regents

Page Last Updated: June 25, 2013
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