In 1982 and 1983, effects of soybean row spacing and irrigation on weed resurgence following postemergence herbicide applications were evaluated. Also, ‘Forrest’ and ‘Ransom’ cultivar effects and early and late planting date influences on weed resurgence were evaluated in 1982 and 1983, respectively. In both years, as row spacing increased, weed resurgence increased. Photosynthetically active radiation measurements indicated the amount of weed resurgence coincided closely with the differing amounts of light penetrating to the soil surface. Irrigation, planting date, and cultivars showed no significant effect on weed resurgence. In 1982, a significant cultivar by row spacing interaction was obtained. In 1983, the late planting date showed a trend for less weed resurgence under irrigated conditions, although the difference was not significant. Soybean canopy measurements indicated development was greater under irrigation.
Canopy height‐to‐row spacing ratio as a simple and practical onsite index to determine the time for terminating
Ipomoea coccinea
control in the Japanese soybean‐growing systems