The methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} mixed with soil at 1, 2, and 3 ppmw reduced the growth of Bromus species in the greenhouse as follows: downy brome (Bromus tectorum L. ♯ BROTE) more than Japanese brome (Bromus japonicus Thunb. ex Murr. ♯ BROJA) more than cheat (Bromus secalinus L. ♯ BROSE). The decrease in herbicide effect (decay) over time was described better using a second-order equation than a first-order equation. Plant response-herbicide dose relationships were described best with a cubic polynomial equation.

Both 14C-clopyralid (3,6-dichloropicolinic acid) and 14C-chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzensulfonamide} were readily absorbed by Canada thistle [Cirsium arvense (L.) Scop. ♯ CIRAR] leaves, with 99 and 75%, respectively, of the applied doses absorbed 144 h after application. Absorbed 14C-clopyralid was rapidly exported from the treated leaves, whereas 14C-chlorsulfuron was translocated much more slowly. After 144 h, 29% of the applied 14C-clopyralid and 5% of the applied 14C-chlorsulfuron were recovered in the roots and developing root buds of Canada thistle plants. Smaller amounts of the two herbicides were absorbed and translocated in perennial sowthistle (Sonchus arvensis L. ♯ SONAR) than in Canada thistle. More 14C-clopyralid than 14C-chlorsulfuron was absorbed and translocated out of treated leaves of perennial sowthistle, but equal amounts, 3 to 4% of the applied doses, were recovered in the roots and root buds 144 h after application. Foliar applications of clopyralid, followed by removal of the treated shoot 24, 72, or 144 h after application, markedly reduced shoot regrowth in both Canada thistle and perennial sowthistle. Similar treatment with chlorsulfuron did not prevent shoot regrowth in either species.

Field experiments were conducted in 1982 and 1983 at Stoneville, MS, to determine the susceptibility of 17 biotypes of bermudagrass [Cynodon dactylon (L.) Pers. ♯ CYNDA] to seven postemergence herbicides. Control, averaged over all biotypes 13 weeks after treatment, varied from 96% using haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} at 0.56 kg/ha to 16% using fenoxaprop {(±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid} at 0.28 kg/ha. Control among biotypes ranged from 89 to 96% using haloxyfop at 0.56 kg/ha and from 4 to 89% using dalapon (2,2-dichloropropanoic acid) at 11.2 kg/ha.

Corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.] were grown for 5 yr in rotation without tillage (no-till), with fall and spring tillage (disk), and with conventional tillage (plow). Weed distribution and weed yields were measured in the final year of the experiment. Grass weed yield, primarily due to green foxtail [Setaria viridis (L.) P. Beauv. ♯ SETVI], was significantly higher in the no-till system. Broadleaf weed distribution and yield were similar in all tillage systems.

Field studies were conducted for 4 yr with HOE-39866 [ammonium-(3-amino-3-carboxypropyl)-methylphosphinate] and for 2 yr with SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate) to compare foliar activities with those of paraquat (1,1’-dimethyl-4,4’-bipyridinium ion) and glyphosate [N-(phosphonomethyl)glycine] in no-till corn (Zea mays L. ‘Pioneer 3320’ in 1981 and ‘Pioneer 3184’ in 1982 and 1983). Rates evaluated were 0.6 to 1.7 kg ai/ha for all herbicides except paraquat which was included at 0.3 and 0.6 kg ai/ha. Control of rye (Secale cereale L.) was excellent at all rates with SC-0224, paraquat, and glyphosate, but HOE-39866 was effective only when combined with residual herbicides. All four herbicides provided good initial control of horseweed [Conyza canadensis (L.) Cronq., ♯ ERICA], but recovery following paraquat application was extensive. Combinations of HOE-39866, SC-0224, and glyphosate at 0.6 kg/ha with atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] at 1.1 to 1.7 kg ai/ha + metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 1.7 kg ai/ha produced antagonistic responses against rye and sometimes horseweed. In 1983, the combination of SC-0224 + residual herbicides provided significantly better control of rye and horseweed 8 days after treatment than the combination of glyphosate + residual herbicides.

In field studies, a preemergence application of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] followed by an early postemergence application of dicamba (3,6-dichloro-o-anisic acid) gave good season-long control of smooth pigweed (Amaranthus hybridus L. ♯ AMACH) in conventional and no-till corn (Zea mays L. ‘Pioneer 3184’ and ‘Pioneer 3382’). In soybeans [Glycine max (L.) Merr. ‘Williams' and ‘Essex’], best control of smooth pigweed was achieved with an early postemergence application of sethoxydim {2-[1-(ethyoxy-imino)butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-1-one} plus acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}. Tillage played a role in the degree of smooth pigweed control. Best control of smooth pigweed in corn was obtained when the ground was moldboard plowed and disced, and least control was obtained when corn was no-till planted in the previous year's corn stalks or in a rye (Secale cereale L.) cover crop.

Bermudagrass [Cynodon dactylon (L.) Pers. ♯ CYNDA ‘Vamont’, ‘Midiron’, and Cynodon dactylon X Cynodon transvaalensis Burlt-Davy ♯ CYNTR ‘Tifway’] cultivars were tolerant to oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1, 3,4-oxadiazolin-5-one] applied at rates up to 4.5 kg ai/ha during sprig establishment. The rate of shoot growth from sprigs after oxadiazon treatment was excellent and provided adequate ground cover within 3 months. Oxadiazon applications adversely affected root development of the Midiron cultivar as measured by the force required to uproot the sod. Root development of Vamont and Tifway after oxadiazon application was equal to that of untreated bermudagrass. Oxadiazon plus bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] was inhibitory to both root and shoot growth of all cultivars. Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] applications at 3 and 5 weeks after sprigging caused severe root injury to Vamont and Midiron bermudagrass.

Absorption and translocation of 14C-dicamba (3,6-dichloro-o-anisic acid) in seven salt formulations were determined 60 h after application to leaves of soybean [Glycine max (L.) Merr. ‘Williams’] grown in nutrient solution. The dimethylamine (DMA) formulation was consistently absorbed and retained in the plant in amounts equal to or greater (46% of recovered 14C) than other formulations (which averaged 19% of recovered 14C) when applied without surfactant. Absorption and subsequent retention of the DMA formulation in the plant was least affected of all formulations by the addition of a surfactant. With a surfactant, absorption of the DMA, monoethanolamine (MEA), and inorganic salt formulations was similar (>75% of recovered 14C). Addition of seven surfactants to the K-salt of dicamba increased both the amount of 14C absorbed by 35 to 56% and the amount recovered in the plant. All surfactants except one enhanced absorption of the K-salt of dicamba to a similar degree. Dicamba exhibited predominantly symplastic translocation with the majority of 14C being recovered in the new second trifoliolate leaves and nutrient solution. As much as 66% of the radioactivity absorbed through the leaves was exuded by roots into the nutrient solution 60 h after leaf treatment.

In a location with cypress spurge (Euphorbia cyparissias L. ♯ EPHCY) and naturally occurring Uromyces scutellatus (Pers.) Lév. s.str., the percent of shoots deformed by this systemic rust increased from 6% in 1981 to 48% in 1982, followed by a decrease in both deformed and normal shoots in 1983 and 1984. After inoculation in 1981 of two cypress spurge crowns at a location near Zürich by teliospores of Uromyces alpestris Tranzsch., more than 80% deformed shoots were obtained in 1983 and 1984. Inoculations of cypress spurge root segments by U. scutellatus s.str. or U. alpestris in experimental plots in 1982 gave 50 to 100% infected plants, and in most cases more than 50% deformed shoots in 1984. The collection of U. alpestris studied (E-52) could be a promising candidate for mycocontrol of cypress spurge because of its pathogenicity and specificity.

Roller-applied picloram (4-amino-3,5,6-trichloropicolinic acid) at a concentration of 30 to 60 g ae/L gave similar control to leafy spurge (Euphorbia esula L. ♯ EPHES) as spray-applied picloram at 1.1 to 2.2 kg ae/ha. Leafy spurge control was most effective when the roller applicator was adjusted to treat a maximum amount of stem tissue with a 60 g/L picloram solution. Control was not improved by including a petroleum oil or surfactant additive. Fall applications of roller-applied picloram tended to provide better control than spring applications. When used on dense leafy spurge stands, the roller applicator applied only 40% as much picloram as spray treatments of 2.2 kg/ha. However, picloram residues in soil following roller application were similar to those from picloram at 0.3 to 1.1 kg/ha applied as a spray.

Honey mesquite [Prosopis glandulosa (Torr.) ♯ PRCJG] was treated with several herbicides and herbicide combinations primarily on the Texas Post Oak Savannah over a 4-yr period. Sprays of glyphosate [N-(phosphonomethyl)glycine], picloram (4-amino-3,5,6-trichloropicolinic acid), 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} generally caused a high degree of canopy reduction in the fall of the year the spraying was done. However, sprays of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) and picloram were the most effective herbicides for killing honey mesquite 1 yr after application. At 1.1 kg ai/ha, clopyralid killed 70 to 95% and picloram killed 20 to 65% of plants 3 yr or older. Picloram plus 2,4,5-T was intermediate in effectiveness. Sprays of 2,4,5-T and triclopyr killed some plants. Picloram and tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} pellets killed few if any honey mesquite. Hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] boluses killed no more than 37% of the honey mesquite at rates up to 4.5 kg ai/ha. Herbicides sometimes killed more honey mesquite with sprouts 2 or 3 yr old than at 1 yr old.

The acetanilide herbicides alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide], the ethyl ester of diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl)glycine], or H-26910, the isopropyl ester of N-(chloroacetyl)-N-(2-methyl-6-ethylphenyl)glycine, failed to inhibit yellow nutsedge (Cyperus esculentus L. ♯ CYPES) tuber sprouting in petri dishes. At 3.5 and 0.35 μM, all herbicides inhibited growth of newly emerging shoots. There was no significant difference in activity among alachlor, metolachlor, diethatyl ethyl, and R-26910 on yellow nutsedge sprouts grown in petri dishes. In soil, metolachlor and alachlor were equally effective for yellow nutsedge control. Both were more effective than H-26910 at high levels of soil organic matter. Diethatyl ethyl was least effective at all levels of soil organic matter. For all herbicides evaluated, activity decreased with increased levels of organic matter in the soil. For acetanilide herbicides to be effective on yellow nutsedge, they needed to be in the soil zone, above or at the level of the tuber.

Fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} controlled annual grasses in cucumbers (Cucumis sativus L. ‘Calypso’ and ‘Poinsett’), cantaloupe (Cucumis melo L. ‘Edisto 47’), zucchini squash (Cucurbita pepo L. ‘Elite’), and sweet potato (Ipomoea batatas L. ‘Jewel’) when applied as single or repeated applications of 0.3 or 0.6 kg ai/ha during 1982 and 1983 in North Carolina. All crops were generally tolerant to fluazifop and yields were equal to cultivated controls in all but one experiment. Residues detected in the various crops by high-performance liquid chromatography (HPLC) decreased as time elapsed between application and harvest increased. Approximately 1 ppm (w/w) of fluazifop was detected in cucumbers at 8 days after application, but residues were below the least detectable limit (0.05 ppm) when cucumbers, squash, and cantaloupe were harvested at 18 to 29 days after application. Fluazifop concentrations were 0.06 ppm or less in sweet potatoes at 55 days after application, and no fluazifop was detected at 84 days after application. Small cucumbers (<12 cm long) had greater fluazifop residues than larger fruit (>12 cm long) 20 days following application.

Significantly higher rates of butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine] were required to produce the same level of weed control as trifluralin [2,6-dinitro -N,N-dipropyl-4-(trifluoromethyl) benzenamine] when applied to soybeans [Glycine max (L.) Merr.] on seven different soils in the field. Higher rates of butralin were also required to control barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯ ECHCG] in growth chamber studies. No differences in the extent of soil adsorption of trifluralin and butralin were apparent; therefore, differences in efficacy could not be attributed to differences in soil adsorption. Herbicide rates required for 80% weed control and Freundlich K-values (adsorption capacity indices) were mostly highly correlated with soil organic-matter content and soil surface area as measured by benzyl ethyl ether (BEE) and ethylene glycol monoethyl ether (EGME) on nine soils. Analysis of the organic-matter content of the nine soils by 10 soil testing laboratories resulted in highly significant differences among laboratories.

An oats (Avena sativa L.) – no-till soybean [Glycine max (L.) Merr.] ecofarming system was evaluated through four, 2-yr rotations during 1978 through 1982. Herbicides were applied to oats, to oat stubble, and to no-till soybeans for maximum weed control throughout the 2-yr rotation. The treatment sets also included conventional tillage of oat stubble for weed control and preparation of a soybean seedbed. Several herbicides gave effective weed control in oats with minimal crop injury; however, grain yield was not increased by any of the treatments. No recropping problems were encountered when planting no-till soybeans 14 months after application of chlorsulfuron {<2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide)}. Soybean yield under ecofarming was greater 1 yr and equal to that with the conventional-tillage system the other 2 yr.

Invasion of rootplowed rangeland by blackbrush acacia (Acacia rigidula Benth. ♯ ACARI) is a problem in south Texas. Low-energy grubbing uprooted plants 1 to 2.5 m tall in densities of 50, 150, and 300 plants/ha at rates of 3.0, 1.6, and 1.0 ha/h, respectively, yielding an average plant kill of 85%. Plants grubbed above the second major lateral root sprouted. A grubbing depth of 20 to 30 cm was necessary to assure plant death. A grubbing blade modified by the addition of ripper teeth facilitated grubbing under dry soil conditions and extended the grubbing season. Contract cost for grubbing the average density of 169 plants/ha was $20.80/ha adjusted to 1983 dollars.

Applications of 1.6 kg ai/ha of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] to established alfalfa (Medicago sativa L. ‘Rambler’) at the start of each growing season for 4 yr increased seed yield by 68% and controlled established dandelion (Taraxacum officinale Weber. in Wiggers ♯ TAROF) and smooth brome (Bromus inermis Leyss. ♯ BROIN). A lesser amount of metribuzin was not sufficient for smooth brome control, and a greater amount damaged the alfalfa. Hexazinone [3-cyclohexyl-6-(dimethylamino)-methyl-1,3,5-triazine-2,4(1H,3H)-dione] applied at 1.0 kg ai/ha also controlled dandelion and smooth brome and produced increases in alfalfa seed yield. Mixtures of terbacil (3-tert-butyl-5-chloro-6-methyluracil) with reduced rates of metribuzin or hexazinone controlled dandelion well, but gave only fair control of smooth brome. Alfalfa seed yield was negatively correlated with the smooth brome population.