Weed and Disease Control In California-Grown Floricultural Crops without Methyl Bromide Soil Fumigation.

The efficacy of reduced rates of fumigant pesticides to control a multi-pest complex under two different types of plastic mulch (low density polyethylene film, LDPE, and virtually impermeable film, VIF) was evaluated in commercial floricultural systems in coastal California relative to the commercial standard MB/Pic soil fumigation at 350 lb/acre and an untreated control. Drip treatments tested were chloropicrin (Pic; 150 lb/acre), InLine (62% 1, 3-D, 35% Pic; 200 lb/acre), Pic60 EC (60% Pic, 35% 1, 3-D; 150 lb/acre), Midas (33% iodomethane, 66% Pic; 150 lb/acre), and MB/Pic (67%/33%; 150 lb/acre). One half of each treatment received a sequential metam potassium (26 gal/acre) application at 5 to 7 days past the first fumigant application. Shank treatments included Pic60 (150 lb/acre, VIF), Telone C35 (200 lb/acre, VIF), Paladin/Pic (83% dimethyl disulfate, 17% Pic; 600 lbs/acre), and Midas (50/50; 150 lb/acre, VIF). Floricultural crops were planted 3 weeks after fumigation, and conventional production practices and pest management were followed. Densities of soil-borne pathogens in soil and bulb samples, propagules of previous crop, native weed populations, and plant growth and health parameters were evaluated at regular intervals during the season. Flower stems and bulbs were harvested, graded, and counted according to size (lengths and circumference, respectively) for quality evaluation. Relative to MB/Pic at 350 lb/acre, reduced rates of MB/Pic and alternative fumigants showed similar or better control of previous crop propagules, native weed spp. and soil-borne pathogens, especially if fumigants were applied under VIF. The sequential application of metam potassium to drip-applied fumigants further increased control of key pathogens significantly. In general, drip applied fumigants showed better control of soil-borne pathogens than shank applied MB/Pic. Flower stem and bulb yield and quality data will be presented.