Weed Pressure, Yield, and Adhesion of Soil-biodegradable Mulches with Pie Pumpkin (Cucurbita pepo)

A soil-biodegradable mulch (BDM) is designed to be tilled into the soil at the end of the growing season, and is a successful alternative to polyethylene (PE) mulch if it suppresses weeds and improves soil temperature and moisture, crop yield, and fruit quality. This study compared one clear plastic BDM (COX), two black plastic BDMs (BOX and BFO), and two paper BDMs (WGP and AMX) to clear and black plastic PE mulch (CPE and BPE, respectively) for weed control, yield, and mulch adhesion of ‘Cinnamon Girl’ pie pumpkin (Cucurbita pepo) in a Mediterranean climate where increased soil temperature from mulch is desirable. BDMs in this study are advertised as soil-biodegradable, and we tested functionality but not biodegradability. Mulch deterioration during the growing season was measured as percent soil exposure (PSE), and remained low at the end of the growing season for all BDM and PE treatments both years (5% on average) except COX (68%). Weed number and biomass were low early, mid, and late season for all treatments except COX in 2018 and COX and CPE in 2019. Soil temperature with PE mulches (20.7 °C on average) was similar or slightly higher than with plastic BDMs (19.8 °C on average), which was higher than with paper BDMs (18.9 °C on average). Total fruit number and yield were similar for PE mulches (19.3 and 24.5 kg, respectively) and black plastic BDMs (17.3 and 21.2 kg, respectively), which were higher than COX and paper BDMs (15.7 and 19.8 kg, respectively). Mulch adhesion occurred on fruit in all BDM treatments, with more mulch adhesion in BFO in 2018 and WGP in 2019 than in other BDM treatments each year. The number of wipes is a proxy for the impact on harvest labor and can influence overall on-farm profitability. The number of wipes to remove adhered mulch (1.2 wipes on average) was similar for fruit harvested at four times of day (0800, 1000, 1200, and 1400 hr), but more wipes were needed to remove adhered mulch when fruit were stored up to 4 hours postharvest (5.4 wipes). Number of wipes to remove adhered mulch was negatively correlated to the amount of moisture on the fruit surface (R² = 0.31). Overall, these findings demonstrate that all black plastic and paper BDMs remained intact throughout the growing season and controlled weeds as well as black PE mulch, while clear BDM had higher weed pressure because it degraded during the growing season. Pumpkin yield was similar for black plastic BDMs and PE mulches and lower for clear and paper BDMs. However, all BDMs in this study adhered to the fruit surface and their removal became more difficult as the fruit surface dried.