The effect of nonionic surfactant, crop oil concentrate, organosilicone surfactant, methylated seed oil, and a blend of organosilicone surfactant and methylated seed oil on absorption of 14C-clethodim was evaluated in barnyardgrass (Echinochloa crus-galli). Absorption of 14C-label was greatest during the first 40 min after application when 14C-clethodim was applied with methylated seed oil or a blend of methylated seed oil and organosilicone surfactant. These adjuvants increased the rate of absorption more than crop oil concentrate, organosilicone surfactant, or nonionic surfactant. Crop oil concentrate was more effective than organosilicone or nonionic surfactant in increasing absorption, with nonionic surfactant being more effective than organosilicone surfactant. These results generally agreed with the order of increasing efficacy of clethodim on barnyardgrass as affected by adjuvants in field experiments. Another study was conducted to determine the effect of bromoxynil on absorption and translocation of 14C-clethodim in yellow foxtail (Setaria glauca). Bromoxynil reduced absorption of 14C–clethodim 4, 8, and 24 h after application and also reduced the amount of 14C-label translocated from the treated leaf. These data suggest that antagonism of clethodim control of yellow foxtail by bromoxynil observed in previous research can be attributed partially to decreased absorption and translocation of clethodim.

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.

Antagonism of quizalofop-P efficacy on annual grasses by bromoxynil has been noted in both the field and greenhouse. Laboratory experiments were conducted on yellow foxtail (Setaria glauca) to determine the effect of mixing bromoxynil with the ethyl ester of quizalofop-P on absorption, translocation, and metabolism of 14C-quizalofop-P Applying bromoxynil in mixture with quizalofop-P reduced 14C-label absorption from 63 to 51%, 73 to 52%, 77 to 68%, and 90 to 80% at 4, 8, 24, and 96 h after treatment, respectively. Translocation of 14C-label from the treated leaf into the shoot above or shoot below was unaffected by bromoxynil. However, translocation into the roots was reduced from 0.9 to 0.4% and 1.0 to 0.5% at 4 and 8 h after treatment, respectively, but differences were not noted at 0.5, 1, 24, and 96 h after treatment. Bromoxynil increased deesterification of quizalofop-P-ethyl into quizalofop-P acid from 45 to 60% in the shoot above the treated leaf. However, bromoxynil did not affect metabolism of quizalofop-P in the treated leaf or shoot below the treated leaf. These results suggest that antagonism of quizalofop-P activity by bromoxynil is primarily due to decreased absorption of quizalofop-P, whereas effects on translocation and metabolism were minor.

Field studies have shown that rimsulfuron can move laterally with mower tires and injure neighboring cool-season grasses, indicating that persistent chemical can dislodge from turfgrass foliage. Laboratory studies were conducted to evaluate persistence and stability of 14C rimsulfuron on perennial ryegrass and annual bluegrass foliage. Rimsulfuron was absorbed by annual bluegrass and perennial ryegrass equivalently, and persisted equally on foliage of each species. When extracted with a water rinse, 57% of applied rimsulfuron was recovered after 10 min, and 42% of applied rimsulfuron was recovered after 96 h. Rimsulfuron was stable 4 d after application based on comparison of rinse water chromatograms to stock solution chromatograms. These data indicate that appreciable rimsulfuron persists on turf foliage for 4 d. Thus, limiting traffic on treated areas for several hours to allow drying is not a viable method to prevent lateral relocation of rimsulfuron, and subsequent injury to cool-season turfgrasses.

Field experiments were conducted to compare large crabgrass control by clethodim or sethoxydim applied alone and with selected fungicides registered for use in peanut. Fluazinam, propiconazole plus trifloxystrobin, or tebuconazole did not affect efficacy of clethodim or sethoxydim. Azoxystrobin, boscalid, chlorothalonil, and pyraclostrobin reduced efficacy of clethodim and sethoxydim in some experiments. Increasing the herbicide rate increased large crabgrass control regardless of the addition of chlorothalonil. In laboratory experiments, 14C absorption was less when 14C-clethodim or 14C-sethoxydim was applied with chlorothalonil. Pyraclostrobin and tebuconazole did not affect absorption of 14C-clethodim or 14C-sethoxydim.

Virginia buttonweed control in warm-season turfgrass species requires high application rates and/or repeated applications of herbicides (or both) with an auxin-type mode of action. These treatments often lead to unacceptable turfgrass injury. Diflufenzopyr functions as a synergist with auxin-type herbicides, and it has been suggested that it may do the same when combined with pyridine herbicides such as fluroxypyr. The objective of this field and laboratory research was to determine whether Virginia buttonweed control could be improved with admixtures of fluroxypyr and diflufenzopyr without unacceptable turf injury. Treatments consisted of fluroxypyr applied alone at 140 and 280 g ae/ha, diflufenzopyr alone at 70 and 140 g/ha, and all possible two-way admixtures. Treatments were applied to a hybrid bluegrass ‘Thermal blue’ infested with Virginia buttonweed. Sod of centipedegrass ‘common’, hybrid bermudagrass ‘Tifway’, hybrid zoysiagrass ‘Emerald’, and St. Augustinegrass ‘Raleigh’, which had been previously established in pots, were treated simultaneously and returned to a greenhouse. Fluroxypyr plus diflufenzopyr at 280 and 70 g/ha, respectively, controlled Virginia buttonweed nearly 40% more than fluroxypyr alone. Turfgrass injury was species-dependent, and was generally either equivalent to or less than that obtained with fluroxypyr alone. Radiotracer studies established that, depending upon the turfgrass species, fluroxypyr absorption was either not influenced or reduced by the addition of diflufenzopyr. Neither root nor foliar absorption of fluroxypyr by Virginia buttonweed was influenced by diflufenzopyr. Translocation of foliar-absorbed fluroxypyr was reduced, but translocation of root-absorbed fluroxypyr was increased by diflufenzopyr. The diflufenzopyr-induced synergism may indicate that a significant portion of the applied fluroxypyr was absorbed by roots or by other subsoil tissues, or both.

Selective placement studies were conducted under greenhouse conditions to determine the relative importance of root vs. foliar absorption of postemergence-applied quinclorac by torpedograss. Foliar + soil and soil-only applications were more effective than foliar-only in reducing torpedograss foliage at 4 wk after treatment (WAT). However, foliar-only and foliar + soil were more effective than soil-only in suppressing regrowth at 10 WAT. Quinclorac foliar absorption by torpedograss and subsequent translocation, as determined with radiotracer techniques, was minimal. After 72 h, only 26% of the applied quinclorac had been absorbed, and 13.7% of the amount applied remained within the treated leaf. Only 0.3% of applied was recovered in the roots, and none was detected in the developing rhizomes. Quinclorac was readily root absorbed and translocated. After 6 h, a 26.7 μg/plant dose of quinclorac had been absorbed, and 54% of this quantity remained in the roots; the remaining 46% having been translocated throughout the plant. The youngest leaf and the immature rhizomes accumulated 5 and 9% of the amount absorbed, respectively. Quinclorac was not readily soil sorbed as determined by soil solution experiments. Quinclorac was displaced nearly concomitant with the wetting front in soil chromatography. Soil solution concentration and soil mobility were greater at pH 6.7 than at 5.7. Results establish that consistent control of torpedograss with quinclorac is dependent on soil entry and root absorption. Unfortunately, the propensity of quinclorac to be water displaced could negatively affect this control.

Research was conducted to evaluate root uptake, translocation, and metabolism of 14C-sulfentrazone alone or in a mixture with clomazone in solution in flue-cured tobacco transplants. Uptake and translocation of sulfentrazone was rapid and was not affected by the addition of clomazone. Fifty-nine and 65% of the 14C absorbed by the plant was translocated to the leaves within 24 h with sulfentrazone alone and in the clomazone plus sulfentrazone mixture, respectively. Differences in plant metabolism were observed between sulfentrazone alone and sulfentrazone plus clomazone. After 3 h, 66% of the 14C recovered from the leaves was metabolized when sulfentrazone was applied alone, compared to 91% when sulfentrazone was applied with clomazone. The difference could indicate that metabolism of sulfentrazone by tobacco transplants was enhanced by the presence of clomazone.

We examined the effect of a postemergence application of fluazifop-P on root uptake, translocation, and metabolism of 14C-terbacil in ‘Kent’ strawberry. Fluazifop-P had no effect on uptake of 14C-terbacil from a nutrient solution over 48 h, nor did it affect the proportional distribution of 14C-label in the plants. The 14C-label was readily translocated to the foliage where it tended to accumulate in vascular tissue. Fluazifop-P reduced the overall conversion of 14C-terbacil to metabolites by about 50%. Thin layer chromatography of methanol extracts of leaflets, petioles, crowns, and roots separated the 6-hydroxymethyl derivative, and several unidentified metabolites, including a major water-soluble metabolite at the origin. At least 50% of the latter could be converted to the 6-hydroxymethyl metabolite by β-glucosidase, but other metabolites could be separated in other solvent systems. The levels of metabolites were generally two- to threefold higher in plants treated with terbacil alone than in those pretreated with fluazifop-P. Therefore, we conclude that the interaction observed between these herbicides in the field results from fluazifop-P inhibiting detoxification of terbacil by strawberry.

Epicuticular wax is a major barrier to the movement of foliar-applied herbicides into plant leaves. Many researchers have evaluated the penetration of herbicides in plants using similar methods. However, the methods used to remove unabsorbed herbicide from the leaf surface have been inconsistent among scientists. Laboratory experiments were conducted to evaluate the effectiveness of various compounds as a leaf wash for removing unabsorbed 14C-labeled herbicides from shattercane and velvetleaf leaves. Product B and Product C provided poor results as a leaf wash compared with water, chloroform, methanol, and Product A. Product A increased the amount of 14C-bentazon removed from velvetleaf by 26% compared with the amount removed by chloroform, methanol, or water. Removal of 14C-nicosulfuron was not different between chloroform, Product A, methanol, or water. Although water was the best treatment for the two salts of 14C-glyphosate, Product A was as good or better than chloroform and methanol.