Walnut farmers in California address air quality issues using contemporary technologies that reduce pesticides, minimize dust and smoke, and reduce airborne particulate matter less than 10 microns (PM 10).
- Reduced Pesticide Use: Walnuts now rank lowest in pesticide use among major nut crops grown in California. California Department of Pesticide Regulation 2012 records for pesticide use show walnuts using 35% less pesticide than almonds and 16% less than pistachios.
- Pheromone Mating Disruption (PMD) for Codling Moth: Puffers (Fig 1) and other pheromone dispensing devices emit the sexually attractive female codling moth pheromone (codling moth is the major worm pest of walnut) disrupting mating. Organophosphate and other broad spectrum insecticides traditionally used for this pest have been dramatically reduced or eliminated in walnut culture due to this PMD technology. Biological control has been coincidently enhanced with pesticide reduction.
Fig 1. Mechanical pheromone emitting devices (“puffers”) for codling moth mating disruption.
- Disease Resistant Rootstocks : The California Walnut Board funded rootstock evaluation program has developed superior paradox walnut rootstocks that not only promote excellent productivity but are resistant to fungal diseases such as Phytophthora and parasitic nematode pests (CVs RX-1, VX-211). Resistant rootstocks have potential for reducing topical pesticide applications and pre-plant soil fumigations, thus “volatile organic compounds” (VOCs) that impair air quality.
- Walnut Blight Management: Walnut blight (see Fig. 2), a major foliar and fruit bacterial disease of walnut, has traditionally required multiple copper/Mancozeb bactericidal sprays in spring for control. California Walnut board funded IPM research has provided growers with an effective program of two early sprays that reduce subsequent spray numbers required for control.
Fig. 2. Walnuts infected with walnut blight
- Alternatives to Fumigation: Available soil fumigants are limited as they reduce air quality. California Walnut Board IPM funded research has demonstrated pre-plant use of grass cover crops can replace need for expensive fumigation in many situations by reducing plant parasitic nematode populations to sub-economic levels.
- Ethephon (Ethrel) to Advance Harvest: Navel orange worm is a major pest of walnuts, commonly infesting nuts after hull split and before harvest; infestation is directly proportional to intervals between hull split and harvest. Harvest delays often require broad spectrum pesticide intervention for protection from this pest. Topical applications of the growth regulator ethephon (Ethrel) at nut maturity were shown within the California Walnut Board’s research program to advance harvest as much as two weeks thus avoiding exposure to this pest and negating need for pesticide application and coincident air contamination. Ethephon is now widely used within the California walnut industry.
- Biological Control of Walnut Aphid: Complete biological control of walnut aphid, previously a major pest of walnut, has been effective with introduction of Trioxys pallidus, a tiny wasp parasite. Biological control is a key component of IPM; this has essentially eliminated walnut aphid pesticide applications, thus air and environmental contamination, unless disrupted with broad spectrum insecticides.