The Importance of Fumigation to the Perennial Crop Nursery Industry in California
There are several primary factors driving fumigation in California nursery production systems. First, soil fumigation is important from an agronomic standpoint by providing control or suppression of a broad spectrum of soil-borne pests including weeds, plant parasitic nematodes and various soil pathogens. Control of these pests ensures a vigorous start to the seedlings or dormant-planted propagative materials and can greatly reduce the cost of weed control in a crop that has relatively few post-plant chemicals available for the control of soilborne pests and weeds. An effective soil fumigation treatment can eliminate or greatly reduce many soil borne pests for the duration of the 14 to 26 month nursery cycle.
Second, and more importantly, regulatory requirements greatly influence fumigation decisions in perennial crop nursery systems. Nursery producers must meet state regulations requiring that planting stock sold outside the county of origin be ‘commercially clean with respect to economically important nematodes’ (Nursery Inspection Procedures Manual (NIPM) ). These regulations have been enacted to ensure that soil-borne pests and pathogens are not spread from infested field nurseries and that establishment and vigor of new fruiting fields is not compromised. While garden roses are not usually planted into commercial settings and are not required by the state of California to meet these regulations, other states and countries accept the California certification program as sufficient to meet their phytosanitary requirements, thus making certification critical to interstate and international marketing of garden rose nursery stock.
Nursery producers can meet these phytosanitary requirements by either fumigating the field using an approved treatment or by conducting a detailed inspection of soil samples and planting stock at the end of the production cycle. If a nursery producer elects to use sampling procedures rather than fumigation to meet the regulations and prohibited nematodes are found in soil or plant samples, further sampling is conducted to delineate the extent of the problem. Nursery stock from the affected area cannot be sold for commercial farm planting and usually is destroyed.
Goals of preplant fumigation in perennial crop nursery systems
Reduce populations of plant parasitic nematodes below detection limits in the root zone of the nursery crop (3-5 feet)
Reduces the risk of spreading economically important nematodes from infested nurseries throughout the state and other production regions
Required by California Department of Agriculture’s Nursery Stock Certification Program
Reduce populations of root pathogens that can limit the establishment and growth of newly planted nursery stock and reduce final product quality or salability.
Reduce in season weed control costs by killing weed seed, seedlings, and vegetative propagules of many weed species before planting the nursery stock
Preplant soil fumigation, thus, reduces the economic risk of a non-saleable nursery crop, and is used most tree and garden rose nurseries in California. Grape vine nursery stock also must meet phytosanitary requirements to be certified in California. However, in contrast to tree and rose growers, some grape nursery producers elect to use the inspection procedures rather than fumigation. A spring planting, relatively shorter nursery production cycle, and market preference for smaller nursery stock allows results in reduced risk for prohibited pests especially if the nursery stock is grown in field not previously planted to grape vineyards or nursery. Grape nursery operations with sandy soils or in long-term nursery areas often use preplant fumigation practices comparable to tree and rose nurseries to reduce the economic and market risks of not meeting phytosanitary regulations.