2018 ASHS Annual Conference

Mulching prepared beds with polyethylene sheets for several weeks before planting can create a ‘stale seedbed,’ reducing weed pressure in a subsequent crop. When clear plastic is used, this practice is called solarization; when black plastic is used, it is known as tarping. Though solarization and tarping have been studied and employed for pest control in warmer regions since the late 1970s, their application to weed management in the Northeast USA is new. We conducted three site-years of field experiments near Orono, ME comparing the efficacy of solarization and tarping for stale seedbed establishment. Solarization and tarping applied for 7 weeks in April-May of 2016 both created excellent stale seedbeds: two weeks after plastic removal, there was zero weed emergence in treatment plots, but significant weed emergence in check plots. Subsequent experimental site-years compared solarization and tarping applied for 2 weeks, 4 weeks, and 6 weeks during the summers of 2016 and 2017. Results were inconsistent between years: across treatment durations, 85% fewer weeds emerged following solarization as compared with tarping during the 2016 season, but in 2017, 94% more weeds emerged following solarization as compared with tarping. Factors that may have contributed to this discrepancy between years include soil moisture conditions and weed species. Notably, Portulaca oleracea (purslane) was abundant in the 2017 field site, comprising 45% of total weeds emergence in check plots, but a disproportionate 84% of weeds emerging in solarization treatments. This heat-tolerant species was not observed in our 2016 field site. In both years, solarization resulted in higher soil temperatures than did tarping. Solarization efficacy increased with treatment duration, but tarping efficacy was not consistently related to treatment duration. Soil biological activity was measured in 2016 only, and was not affected by treatment while mulch was in place. However, two weeks after plastic removal, soil biological activity was suppressed 18% following tarping and 43% following solarization in comparison with the check, suggesting that these practices can impact soil microbial communities. Overall, our results suggest that the relative efficacy of solarization and tarping for weed control in the Northeast USA may be context dependent.