- Cover crop establishment in late-season crops, like sweet corn, may be difficult due to the relatively short operational window following crop harvest. In regions like western Oregon, where fall-precipitation can occur when the crop is still in the field, cover crops may not be able to be planted, due to risks of soil compaction or issues excess crop biomass incorporation, and delaying cover crop planting past September 15th reduces the chances of cover crop establishment. Drill interseeding (or relay planting) cover crops can increase seed to soil contact, improve seed germination, and cover crop success. Manipulating sweet corn canopy may increase the amount of photosynthetically active radiation (PAR) that penetrates through the canopy, increasing the chances of successful cover crop establishment following interseeding. Research over two years using cvs. ‘Captain’ and ‘Coho’ found no significant differences in NO3-N reduction between interseeded cover crops and check plots. Interseeded cover crop dry matter (DM) biomass production and N uptake varied between cover crops (43-268 kg•ha-1 and 1.2-7.5 kg N•ha-1, respectively) during the season. In 2017, interseeded cover crops reduced yield by an average of 19% compared to the check, while in 2018, yield was only reduced by an average of 3.4%; however, the effect was highly variable and not significant for either years. In both years, using OSU recommended fertility practices kept soil NO3-N low at harvest, which confounded the evaluation of interseeded cover crop NO3-N scavenging potential. The response of interseeded cover crop mix of Avena sativa (‘Cayuse’ spring oat) and Vicia sativa (common vetch) to canopy manipulation was investigated in 2017 and 2018 using three sweet corn varieties (‘Spring Treat’, ‘Bodacious’, and ‘Coho’), planted in either a north-south (NS) or east-west (EW) orientation. Each variety was either topped above the ear leaf or not at mid-season. Topping sweet corn at the R1 growth stage reduced leaf area index (LAI), but did not consistently affect cover crop biomass at harvest across the two years of the study. Crop row orientation did not appear to affect interseeded cover crop growth and biomass at harvest. Cover crop response was variable between years, and results in 2018 did not agree with 2017. Sweet corn variety was shown to influence the growth of interseeded cover crops more than row orientation or topping. Cover crop biomass production increased in the following order: ‘Coho’ < ‘Bodacious’ < ‘Spring Treat’. The suppressive effect of sweet corn variety on cover crop persisted following harvest; however, rapid cover crop growth in spring negated any effect of row orientation, sweet corn variety, or topping. Observations across two years suggest that altering grower production practices may not be necessary when incorporating interseeded cover crops into sweet corn.