|Koger Iii, Clifford|
Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2004
Publication Date: 5/1/2005
Citation: Koger III, C.H., Reddy, K.N. 2005. Glyphosate efficacy, absorption, and translocation in pitted morningglory (ipomoea lacunosa). Weed Science 53:277-283. Interpretive Summary: Glyphosate efficacy on pitted morningglory is often variable and inadequate when applied at rates typically used by producers. Little information as to why this vining weed species is so difficult to control with glyphosate is available. Thus, greenhouse and laboratory studies were conducted at the Southern Weed Science Research Unit, Stoneville, MS to examine the effects of portion of plant treated with glyphosate control, absorption, and translocation in pitted morningglory. Absorption and movement of glyphosate was rapid and increased with time. Control was often similar when any portion of the plant or the entire plant were treated with glyphosate. These results show that pitted morningglory tolerance to glyphosate increases with increasing plant size, regardless of level of glyphosate spray coverage.
Technical Abstract: 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 18.8% at 1 h after application (HAA) to 44.4% at 192 HAA. The amount of 14C translocated with time ranged from 0.4% at 1 HAA to 25.3% at 192 HAA. 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 HAA 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 (5.1 to 6.1%) 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 of pitted morningglory plant portion to glyphosate was as effective as entire plant exposure, and control with glyphosate is more affected by rate than the degree of plant exposure to glyphosate.