2019 ASHS Annual Conference

Strawberry remains a primary crop in coastal California with annual value > $2bln. At the end of fall-planted strawberry season plant collapse due to soil-borne wilt pathogen Fusarium oxysporum f. sp. fragariae and unrestricted growth of yellow nutsedge (Cyperus esculentus) are increasingly common. End-season fumigation of existing beds with metam products can reduce pathogen and weed survivorship and carryover into next production season. At Oxnard, CA we conducted two trials in 68-inch beds with end-season injections via two drip lines per bed in 2015 (213 lbs/acre of metam sodium) and in 2018 (174 lbs/acre of metam potassium). Nutsedge tubers and Fusarium chlamydospores (survival structures) in sand bags or pathogen infested strawberry crowns were placed at two depths and at two locations in beds. In both years 80-100% of nutsedge tubers germinated in untreated soil. Fumigants reduced shoot production from tubers under drip lines to 0-5% in both years, but between drip lines only to 35% (2015) and 53% (2018). Shoot production was similar at 6 and 12-inch depths. Fumigants provided nearly compete (>95%) control of Fusarium chlamydospores compared to untreated soil. As with nutsedge, pathogen mortality was consistently lower in soil between drip lines compared to locations under drip lines that supplied fumigants. Viable Fusarium recovery from infested crowns was 50-90% in fumigated soil and generally not different from untreated soil. Fusarium-infested crowns and roots are known to harbor pathogens from fumigants and that was the case in these trials. However, end-season fumigation with metam products was very effective in reducing soil-borne inoculum and nutsedge tubers at costs 40-60% lower compared to standard chloropicrin fumigation.