Dose-response of plasticulture summer squash and triploid watermelon to fomesafen applied pre-transplanting

Abstract Dose-response trials to determine the tolerance of summer squash and watermelon to fomesafen pre-transplant (over-the-top of black polyethylene mulch and respective row middles) were performed between 2020 and 2021 at three Indiana locations: the Meigs Horticulture Research Farm (MEIGS), the Pinney Purdue Agricultural Center (PPAC), and the Southwest Purdue Agricultural Center (SWPAC). Summer squash trials were performed at MEIGS and PPAC and watermelon trials were performed at MEIGS and SWPAC. The experiments for both summer squash and watermelon had a split-plot arrangement in which the main plot was herbicide rate, and the subplot was cultivar. Summer squash injury included necrotic leaf margin, chlorosis, brown and white spots, and stunting. Fomesafen rates from 262 to 1,048 g ai ha-1 in 2020 at both locations and from 280 to 1,120 g ai ha-1 in 2021 at MEIGS did not affect summer squash yield. However, in 2021 at PPAC, rates from 280 to 1,120 g ha-1 delayed summer squash harvest and decreased marketable yield from 95 to 61% of the non-treated control. Watermelon injury included bronzing and stunting. Fomesafen rates from 210 to 840 g ai ha-1 did not affect marketable watermelon yield and fruit number. Crop safety was attributed to rain washing off most of the herbicide from the polyethylene mulch before transplanting or to little to no rain after transplanting. Inury was only observed when there was no rain before transplanting followed by excessive rain shortly after transplanting. Overall, the 1x rates used for each trial were safe for use 1 d before transplanting summer squash and 6 to 7 d before transplanting watermelon.