Morningglory interference with triploid watermelon and cucurbit tolerance to fomesafen
Creators: name: Cordonero, Jeanine Auxiliador Arana
Publisher: name: Purdue University Graduate School
Year: 2022
Subjects: Horticultural crop protection (incl. pests, diseases and weeds)

description: Indiana is among the top 10 cucurbit-producing states. Growers identified interference from troublesome weeds such as morningglory spp. (<em>Ipomoea </em>spp.) and a lack of registered herbicides as barriers to production. Thus, experiments were developed to determine (1) the interference of <em>Ipomoea </em>spp. with triploid watermelon, (2) the tolerance of pumpkin to fomesafen herbicide applied preemergence, and (3) the tolerance of plasticulture summer squash and watermelon to fomesafen herbicide applied pre-transplanting. 1) An additive design study was performed in 2020 at the Meigs Horticulture Research Farms (MEIGS) - Lafayette, IN and the Southwest Purdue Agricultural Center (SWPAC) - Vincennes, IN, to evaluate the interference of <em>Ipomoea </em>spp. with watermelon. The presence of <em>Ipomoea</em> spp. densities increasing from 3 to 24 per 27 m<sup>2</sup> increased watermelon yield loss from 58 to 99%, reduced watermelon fruit number 49 to 98%, reduced watermelon fruit weight 17 to 45%, and reduced watermelon aboveground biomass 83 to 94%. The most likely reason for watermelon yield loss was interference with photosynthesis and consequently less dry matter being partitioned into fruit development. Yield loss was attributed to fewer fruit and the reduced weight of each fruit. 2) Dose-response trials were performed in 2020 at SWPAC and in 2021 at SWPAC and the Pinney Purdue Agricultural Center (PPAC) - Wanatah, IN, to evaluate the tolerance of pumpkin to the herbicide fomesafen applied preemergence. Increasing the fomesafen rate from 280 to 1,120 g ha<sup>-1</sup> decreased emergence from 85 to 25% of the non-treated control at SWPAC in 2020, but only from 99 to 74% at both locations in 2021. The severe impact on emergence at SWPAC in 2020 was attributed to the herbicide moving into the crop’s root zone due to excessive rainfall. Fomesafen is highly mobile under water-saturated soil conditions, especially in soils with low organic matter content, high pH, and a high proportion of sand content. Injury included brown and white spots and chlorosis due to the herbicide splashing from the soil surface onto the leaves and included stunting, but injury was transient. As the fomesafen rate increased from 280 to 1,120 g ha<sup>-1</sup>, the predicted marketable orange pumpkin yield (kg per plot) decreased from 95 to 24% of the non-treated control at SWPAC in 2020 and 98 to 74% at PPAC in 2021. The predicted marketable orange pumpkin number decreased from 94 to 21% at SWPAC in 2020 and 98 to 74% at PPAC in 2021. Fomesafen rate did not affect marketable orange pumpkin yield and fruit number at SWPAC in 2021 and did not affect individual marketable orange pumpkin weight at any location-year. Overall, the fomesafen rate of 280 g ha<sup>-1</sup> is safe for use in the pumpkin cultivars 'Bayhorse Gold' and 'Carbonado Gold' within one day after planting, but there is a risk of increased crop injury with increasing rainfall. 3) Dose-response trials were performed in 2020 and 2021 at MEIGS, PPAC, and SWPAC to evaluate the tolerance of summer squash and watermelon to fomesafen applied pre-transplanting. Fomesafen rates increased from 262 to 1,048 g ai ha<sup>-1</sup> in 2020 at both locations, and from 280 to 1,120 g ai ha<sup>-1</sup> in 2021 at MEIGS did not affect summer squash yield. However, in 2021 at PPAC, rates from 280 to 1,120 g ha<sup>-1</sup> delayed harvest and decreased predicted marketable yield from 95 to 61% of the 0 g ha-1 non-treated control. Fomesafen rates increased from 210 to 840 g ai ha<sup>-1 </sup>did not affect marketable watermelon yield and fruit number. Crops’ safety was attributed to rain washing off most of the herbicide from the plastic before transplanting or no excessive rain after transplanting. At PPAC in 2021, summer squash injury was attributed to excessive cumulative rain shortly after transplanting and no rain before transplanting. Overall, the 1x rates used for each trial are safe for use 1 d before planting summer squash and 6 to 7 d before transplanting watermelon. Rainfall before transplanting may be necessary to reduce the risk of the herbicide moving into the crop’s root zone through the punched hole.