Greenhouse and laboratory studies were conducted to examine the effects of site of plant exposure to glyphosate spray on efficacy, absorption, and translocation in pitted morningglory. Absorption of ¹⁴C-glyphosate in four-leaf pitted morningglory gradually increased with time from 19% at 1 h after treatment (HAT) to 44% at 192 HAT. The amount of ¹⁴C translocated with time ranged from 0.4% at 1 HAT to 25% at 192 HAT. Vining 1-m tall plants were controlled 75 to 100% when the top-, middle-, bottom one-third, or entire plant was treated with 1.38 or 2.76 kg ha⁻¹ glyphosate, with control affected more by glyphosate rate than plant section exposed to glyphosate spray. Absorption of ¹⁴C-glyphosate at 96 HAT was similar whether it was applied to the top-, middle-, bottom one-third, or entire plant of 1‐m tall pitted morningglory. The amount of ¹⁴C translocated out of the treated area (5 to 6%) did not differ whether it was applied to top-, middle-, or bottom one-third plant section. Results indicate that absorption and translocation of ¹⁴C-glyphosate in pitted morningglory was rapid and increased with time. Treating any one-third section of pitted morningglory plants was as effective as entire plant exposure, and control with glyphosate is more affected by rate than the degree of plant exposure to glyphosate.

Nomenclature: Glyphosate; pitted moringglory, Ipomoea lacunosa L. IPOLA.