On-farm evaluations of non-fumigant nematicides on cucurbits

Abstract Non-fumigant nematicides were evaluated on cucurbits in two commercial farms in 2017 (Cucumis sativus and Cucumis melo) and three commercial farms in 2019 (Cucumis sativus, Cucurbita pepo and Citrullus lanatus). In 2017, non-fumigant nematicides (fluopyram, oxamyl, fluensulphone, and Majestene) were applied as stand-alone rescue treatments in a cucumber and cantaloupe field heavily infested respectively with Meloidogyne javanica and M. hapla. In 2019, non-fumigant nematicides (fluopyram, oxamyl, and Majestene) were applied both as stand-alone treatments, and as mixtures, in (i) a cucumber field (same as 2017) having a high population of M. javanica, (ii) a squash field previously planted with strawberry and having a high population of M. hapla, and (iii) a watermelon field, previously known to have a high population of sting nematode (Belonolaimus longicaudatus). In 2017, an additional tomato greenhouse study was conducted using the soil from both fields. Both fields in 2017 were re-planted following the rescue nematicide applications, and in the cantaloupe field the new crop established well enough to allow for commercial harvesting. All nematicide treatments in the 2017 cantaloupe field, except for oxamyl, were able to significantly reduce M. hapla root infection after 70 days. Oxamyl did reduce M. javanica root infection in the 2017 cucumber field after 30 days, but the re-planted crop did very poorly, and the field was abandoned after less than one month. In the greenhouse tomato trial, similar trends were observed with better efficacy of the nematicides against M. hapla as compared to M. javanica. In 2019, stand-alone applications of oxamyl and Majestene, and especially the fluopyram + Majestene cocktail significantly reduced the end-season soil population of M. javanica in the cucumber field. No significant effect of any of the products or cocktails was noted on B. longicaudatus in the watermelon field. In the squash field, oxamyl by itself tended to increase soil population of M. hapla, but the mixed application of fluopyram + oxamyl showed some suppression of M. hapla. In both 2017 and 2019 field trials, plant vigor and yield were not significantly affected by the application of any of the nematicides or cocktails. While the nematicides provided better suppression of M. hapla as compared to M. javanica in 2017, the opposite was noted in 2019. This was probably related to the more severe nematode pressure in 2017, especially in the M. javanica field. M. hapla populations tended to decrease during the spring season as soil temperatures increased, while the more tropical B. longicaudatus and especially M. javanica populations increased during the season. Results from this study indicate that although all three nematicides offer an opportunity for cucurbit growers in Florida to help manage nematodes during the cropping season, their efficacy in terms of reducing soil population density or root gall severity, will be dependent on the time of the year, the type of cucurbit that is grown, and the species of nematode present. Some evidence was shown of improved efficacy when nematicide cocktails were applied, but more research is needed to investigate this.