Evaluation of Pic-clor 60 [choloropicrin pre-mixed with 1,3 dicholoropropene] and soil-applied fungicides for the Fusarium wilt management in watermelon

Watermelon (Citrullus lanatus var. lanatus) yield losses due to Fusarium wilt can be considerable and have been increasing in the United States, mainly due to the emergence of the new races of Fusarium oxysporum f. sp. niveum (FON). One of the potential management strategies to reduce Fusarium wilt is the use of fumigants and soil-applied fungicides. Field experiments were conducted in 2018 and 2020 to evaluate fumigant Pic-clor 60 (choloropicrin pre-mixed with 1,3 dicholoropropene) with post-plant soil-applied fungicides (prothioconazole and pydiflumetofen) for their effectiveness against Fusarium wilt. The field was fumigated 21 days before transplanting, and three applications of either fungicide were made at 14-day intervals via a drip irrigation system starting a day after transplanting. In 2018, based on the disease ratings at harvest maturity, all treatments significantly reduced final disease incidence compared to the non-treated control, and the highest reduction was observed when the fumigant was applied at 336.26 kg/ha along with either fungicides. The application of fumigant, together with either fungicides, had significantly higher reduction in disease incidence compared to the stand-alone application (fumigant or fungicides). Also, Pic-clor 60 at 336.26 kg/ha provided a higher reduction in disease incidence than Pic-clor 60 at 280.21 kg/ha. In 2020, results showed a similar trend to 2018, where Pic-clor 60 at 336.26 kg/ha in combination with either prothioconazole or pydiflumetofen had significantly lower final disease incidence. The reduction in disease incidence in Pic-clor 60 at 336.26 kg/ha was higher compared to a lower application rate of 280.21 kg/ha, either when applied alone or in combination with either fungicides. The results presented here are the first to demonstrate that the fumigant Pic-clor 60 along with soil-applied fungicides, pydiflumetofen or prothioconazole may provide an effective management option for Fusarium wilt of watermelon.