Greenhouse and laboratory experiments were conducted to study activity, rainfastness, absorption, and translocation of glyphosate with and without a nonionic organosilicone surfactant in purple nutsedge. Purple nutsedge responded differently to glyphosate depending on growth stage. Glyphosate at 2.24 kg ai/ha in 17-d-old and at 4.48 kg/ha in 10-wk-old plants controlled purple nutsedge at least 96%. Regrowth of plants and tuber resprouting were greatly reduced in these treatments. Organosilicone surfactant did not increase efficacy of glyphosate. A simulated rainfall of 2.5 cm (7.5 cm/h intensity) at 1 and 24 h after glyphosate application reduced efficacy by one-half and one-third, respectively, compared with no simulated rainfall. A rain-free period of 72 h prevented loss of glyphosate activity. Absorption of 14C-glyphosate increased from 2.8% at 1 h after application to 21.4% at 168 h after application and translocation increased from 0.43% at 1 h after application to 5.18% at 168 h after application. Organosilicone surfactant did not affect absorption and translocation of glyphosate in purple nutsedge.

Absorption, translocation, and metabolism of rimsulfuron were studied in three solanaceous weeds. Eastern black nightshade is sensitive (> 95% injury), hairy nightshade is moderately sensitive (50 to 99% injury), and black nightshade is tolerant to rimsulfuron postemergence (POST). Seedlings at the four- to six-leaf stage were treated with foliar-applied 14C-labeled rimsulfuron for 3, 6, 24, and 48 h after treatment. Absorption of rimsulfuron by all weeds increased with time. Black and eastern black nightshade absorbed comparable amounts of radioactivity at each exposure time. Hairy nightshade absorbed less radiolabeled herbicide than the other two nightshades at any treatment time. Hairy nightshade absorbed 54% of the applied radioactivity at 48 h, compared to 74% absorbed by the other weeds. Translocation of rimsulfuron out of the treated leaf was rapid in all species. Black and eastern black nightshade translocated 50 to 70% of the absorbed radioactivity out of the treated leaf with 40 to 50% moving to the upper foliage. In hairy nightshade, about 40% of the absorbed radioactivity translocated out of the treated leaf with equal amounts moving to the upper and lower foliage. Metabolism of 14C-rimsulfuron was rapid in the three nightshades with approximately 54% remaining as rimsulfuron at 3 h after treatment. The levels of the detected metabolites of rimsulfuron were similar in the three nightshade weeds. Differential early uptake and translocation may account for the differential sensitivity of these nightshade species to rimsulfuron.

The absorption, translocation, and metabolism of the ethyl ester of chlorimuron and nicosulfuron in resistant (R) and susceptible (S) smooth pigweed (Amaranthus hybridus) were investigated. R and S smooth pigweed seedlings (5 to 10 cm tall) were treated with foliar-applied 14C-labeled chlorimuron and nicosulfuron and harvested at 3, 6, 24, and 72 h after application. Chlorimuron absorption increased with time in both populations of smooth pigweed and was higher in the R accession only at 6 h after application. Nicosulfuron absorption did not increase with time in the R accession, and after 6 h, there were no differences between the R and S accessions. Absorbed chlorimuron and nicosulfuron were translocated to shoots and leaves above and below the treated leaf, but not into the roots in both accessions. Translocation of chlorimuron and nicosulfuron out of the treated leaf was also similar in the two accessions. Metabolism of 14C-chlorimuron occurred more rapidly in the R accession with approximately 68% remaining as chlorimuron at 3 h after application. At the same time period, 81% of the absorbed radioactivity remained as chlorimuron in the S accession. Metabolism of 14C-chlorimuron at 24 and 72 h after application was greater in the S than the R accession of smooth pigweed. Metabolism of 14C-nicosulfuron was similar in the two accessions and did not increase with time. Rapid herbicide metabolism may explain the twofold level of crossresistance of the R accession of smooth pigweed to chlorimuron at the whole plant level.

Greenhouse and growth chamber experiments were conducted to study glyphosate efficacy, rainfastness, absorption, and translocation in redvine. Glyphosate at 0, 0.56, 1.12, 2.24, and 4.48 kg ai/ha was applied to redvine plants raised from rootstocks at the five- to seven-leaf stage (about 25 cm tall). Redvine control ranged from 55% at 0.56 kg/ha glyphosate to 98% at 4.48 kg/ha. Glyphosate at rates above 1.12 kg/ha, greatly reduced regrowth from rootstocks of treated plants. A simulated rainfall of 2.5 cm (7.5 cm/h intensity) within 24 h of glyphosate application reduced efficacy by 23% compared with no simulated rainfall. Absorption of 14C-glyphosate in redvine increased from 1.8 to 21.9%, and translocation increased from 0.1 to 8.1% from 6 to 192 h after application, respectively. Translocation was both acropetal and basipetal, and by 96 h of exposure, the 14C radioactivity was widely distributed throughout the plant. Absorption and translocation was greatly affected by posttreatment temperature. Absorption and translocation were highest (34.9 and 10.6%, respectively) in plants maintained at 35/30 C (14/10 h, day/night), followed by 15/10 C (21.2 and 4.9%, respectively), and was lowest (7.8 and 1.6%, respectively) in plants maintained at 25/20 C. Results suggest that longer periods of leaf exposure to the herbicide and high temperatures could increase glyphosate absorption, translocation to redvine rootstocks, and subsequent control. These data also suggest that effective control of redvine in the field will require glyphosate rates higher than those recommended for use in glyphosate-resistant crops.

The effects of pelargonic acid and rainfall on glyphosate activity, absorption, and translocation in trumpetcreeper were investigated. Four- to six-leaf–stage plants raised from rootstocks were treated with glyphosate at 0, 0.42, 0.84, 1.68, and 3.36 kg ae/ha. Glyphosate at 1.68 kg/ha and higher controlled trumpetcreeper >98% and completely inhibited regrowth from rootstocks of treated plants. A simulated rainfall of 2.5 cm water applied at 6 h after glyphosate application (HAA) reduced efficacy by one-fifth compared with no rainfall. Absorption of 14C-glyphosate in trumpetcreeper increased from 2.3 to 20.2%, whereas translocation increased from 0.4 to 10.5% from 6 to 192 HAA. At 192 HAA, 9.7% of the recovered 14C-label remained in the treated leaf, 0.6% moved above the treated leaf, and 9.0% moved to fibrous roots and rootstock. The addition of pelargonic acid to glyphosate did not improve glyphosate absorption or translocation or synergize activity in trumpetcreeper compared with glyphosate alone. These results suggest that a 24-h rain-free period and 4 d without disturbance from tillage could maximize glyphosate absorption and translocation in trumpetcreeper.