Challenges and Objectives
The primary factor slowing adoption of methyl bromide alternatives are state regulations related to the Nursery Stock Nematode Certification program. In order to be certified as nematode-free (and, thus, salable) nurseries must either use an approved treatment or undertake a comprehensive soil and root sampling program. The current threshold for parasitic nematodes in California nurseries is “detection”. Thus, if a certified treatment is not used and parasitic nematodes are detected in a nursery block at the end of the growing cycle, the planting stock is non-salable which can result in complete economic loss of a crop valued at $30,000 to $80,000 per acre. Click here for current federal and state regulatory requirements.Research efforts have identified several fumigant treatments that effectively control nematodes and pathogens in some cropping situations but the only MB alternative currently approved for meeting California’s nursery certification requirements is 1,3-dichloropropene (1,3-D) [eg. Telone II and Telone C35]. However, these products are only approved for use in nurseries with coarse-textured soils because the maximum rate allowed in California (332 lb/A) is not sufficient to provide adequate pest control in fine-textured soils. Although 1,3-D-based products are not allowed in all soil types, a significant portion of the perennial crop nursery industry could transition to these products and still meet nematode certification requirements. Widespread adoption of 1,3-D in California’s perennial crop nursery industry is limited by several factors including grower comfort and confidence in a production system based on methyl bromide. Effective fumigation with 1,3-D requires a much greater attention to proper soil preparation and moisture management to ensure adequate distribution of the fumigant both laterally and horizontally in the soil profile. Second, township caps and large buffer zone requirements have been established due to human exposure concerns (bystanders, field workers, neighbors) which also limit 1,3-D fumigation in some areas. Third, preplant fumigation and hand labor are the primary weed control practices in many nurseries; thus, adoption of 1,3-D in the nursery industry also is limited due to concerns about less effective weed control compared to MB. Finally, air quality concerns in California will likely result in greater regulation on pesticides classified as volatile organic compounds (VOC), which may further reduce the ability of fumigant dependant agricultural sectors to convert from MB to 1,3-D for preplant fumigation.