Methyl bromide alternatives for Phytophthora capsici on Michigan's cucurbit crops

Michigan growers are important suppliers of cucurbits for the fresh market. The state's growers used methyl bromide to manage the soilborne pathogen Phytophthora capsici and had extended use of the fumigant via critical use exemptions. P. capsici is widespread, persistent in production fields, and resistant to the fungicide mefenoxam. Alternative fumigants are difficult to use in Michigan as spring soils can be too cold and wet for effective fumigation and subsequent aeration. Data were collected regarding control of P. capsici on cucurbit crops using alternative fumigants or fungicides. Fumigation studies were conducted at commercial production sites, comparing methyl bromide alternatives iodomethane/chloropicrin (Midas), metam sodium (Vapam), metam potassium (K-Pam), chloropicrin (100% Chlor-O-Pic), and 1,3-dichloropropene/chloropicrin (Telone C-35) with methyl bromide. Drip irrigation applications of sodium azide (SEP 100) and the biofumigant, furfural (MultiGuard), were also tested. Data suggested that MultiGuard does not provide significant control of P. capsici as either a pre- or post-planting treatment. Applications of SEP 100 caused severe stunting and death to vegetable crops. K-Pam, Chlor-O-Pic, K-Pam + Chlor-O-Pic, methyl bromide/chloropicrin limited disease when used in a raised bed, plastic mulch system. Telone C-35 and Midas provided inconsistent control. Fungicide studies were conducted on non-fumigated sites infested with P. capsici using products applied to the soil via drip or as foliar sprays. Applications of soil fungicides typically reduced disease while foliar sprays were tested for control of fruit rot. The fungicides oxathiapiprolin (Orondis), fluopicolide (Presidio), and mandipropamid (Revus) are used by growers along with cultural strategies to grow cucurbits with reduced risk of disease.