Root-knot nematode management for pepper and squash rotations using plasticulture systems with fumigants and non-fumigant nematicides

Multi-cropping of vegetables on the same plastic mulch builds up the population of root-knot nematodes (RKN; Meloidogyne spp.), which can severely reduce crop growth and yield. Vegetable growers in the southeastern US usually fumigate soil while laying the plastic mulch in the spring. They then apply non-fumigant nematicides via drip irrigation systems for subsequent crops grown on the mulch. With the advent of new and emerging nematicides, this research was aimed to investigate the best chemical control practice for M. incognita in a pepper and squash plasticulture system. Field trials were conducted in the spring (pepper) and summer (squash) of 2019 and 2020. The spring treatments were soil fumigants of 1,3-dichloropropene, allyl isothiocyanate, and 1,3-dichloropropene plus chloropicrin (Pic60), a RKN-resistant cultivar (Carolina Wonder), and an untreated check. Summer treatments were the non-fumigant nematicides fluopyram, fluensulfone, fluazaindolizine, oxamyl, and Burkholderia spp. strain A396. All spring treatments, except allyl isothiocyanate, reduced (P < 0.05) root galling compared to the untreated check at pepper harvest. At the end of the season, the population density of M. incognita in the soil was only lower (P < 0.05) for the RKN-resistant cultivar treatment than that of the untreated check. Though the RKN-resistant cultivar treatment had the lowest (P < 0.05) soil RKN population and significantly reduced root galling, it had the lowest pepper fruit yield. In contrast, pepper associated with Pic60 treatment had the highest fruit yield. For the summer trial, squash plots treated with fluensulfone had the lowest root gall index and oxamyl had the highest (P < 0.05); however, no difference was observed between fluensulfone and oxamyl with other treatments. In 2019, plots treated with Burkholderia spp. and fluensulfone had higher fruit yield (P < 0.05) than fluazaindolizine; however, squash yield was similar among the treatments in 2020. This study suggests that Pic60 (a mix of nematicide and fungicide active ingredients) is likely an ideal fumigant to apply when laying the plastic mulch because of its broad-spectrum effect, and any of the nonfumigant nematicides may be used in RKN control on squash.