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 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.

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.

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.

Pelleted tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} was hand broadcast at 2.2 and 4.5 kg ai/ha every month for 2 yr on an area infested with live oak (Quercus virginiana Mill. ♯4 QUEVI), post oak (Q. stellata Wangenh. ♯ QUESL), parsley hawthorn (Crataegus marshallii Egglest. ♯ CSCMS), and yaupon (Ilex vomitoria Ait. ♯ ILEVO) on the Gulf Coast Prairie near Cordele, TX. Live oak, post oak, and parsley hawthorn trees were killed at most rates and dates of tebuthiuron application. Applications of 2.2 kg/ha of tebuthiuron killed 90% or more of the yaupon plants when it was applied in October and December 1975 and February, March, and June 1976 and less than 90% when applied at other dates. On another site, pelleted tebuthiuron was aerially applied at 2.2 and 4.5 kg/ha every 3 months during 1978 and 1979 in the Post Oak Savannah near Bryan, TX. At 2.2 kg/ha, tebuthiuron killed all post oak and 80% or more of the blackjack oak (Q. marilandica Muechh.), yaupon, winged elm (Ulmus alata Michx. ♯ ULMAL), and mockernut hickory (Carya tomentosa Nutt.) regardless of date treated. Tree huckleberry (Vaccinium arboreum Marsh.) killed by tebuthiuron when applied at 2.2 kg/ha ranged from 34% in July 1979 to 69% from application in February 1978. Application of 4.5 kg/ha of tebuthiuron killed 83% or more of the tree huckleberry when it was applied in January and April 1978 and January, April, July, and October 1979. Herbaceous plant cover usually increased by the second season.

After 45 weeks, between 5 and 8% of the applied radioactivity from 14C-chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} applied to small sandy loam plots was recovered as chlorsulfuron and about 15% as 2-chlorobenzenesulfonamide. After 95 weeks, 2% of the original radioactivity remained as chlorsulfuron and 20% as the sulfonamide. The persistence of formulated chlorsulfuron was investigated using small field plots at two locations for three successive years. Between 3 and 16% of the herbicide applied during May was detected in the top 10-cm soil layers the following May using a corn-root (Zea mays L.) bioassay procedure.

Adsorption of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl) amino] carbonyl] benzenesulfonamide} on four soils having different pH values (6.2 to 8.1) was low. Log/log Freundlich isotherms for all soils at 8 and 30 C were linear, the extent of adsorption being greater at 8 than at 30 C. There was an inverse relationship between pH and degradation rate with a half-life of 88.5 days at pH 6.2 and 144 days at pH 8.1 at 20 C. Rapid disappearance was noted during the first 15 days after application. With decreasing moisture and temperature, chlorsulfuron degraded more slowly. The half-life ranged from 229 days at 10 C and moisture content of 75% field capacity to 62.5 days at 40 C and 75% field capacity at pH 7.7.

The phytotoxicity of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl] benzenesulfonamide} was compared in six soils, and the relationship of activity to soil physical and chemical properties was evaluated. The influence of soil pH (4.2 to 7.8) on phytotoxicity and adsorption of chlorsulfuron incorporated into high-organic-matter soil was also studied. For the phytotoxicity studies, corn (Zea mays L. ‘Pioneer 3320’) was used as the bioassay plant. Organic matter was the soil variable most highly correlated with chlorsulfuron phytotoxicity. There was an inverse relationship between phytotoxicity and organic matter. No significant relationship between clay content and chlorsulfuron toxicity was observed. The adsorption of chlorsulfuron decreased with increasing soil pH while desorption was greater at alkaline pH. Phytotoxicity of chlorsulfuron increased with increasing soil pH and reached a maximum at pH 6.9.

Plant canopy reflectance over the 0.45- to 1.25-μm wavelength (WL) of weed species and crops was recorded with a field spectroradiometer to evaluate the possible use of remote sensing to distinguish weeds from crops. Weed and weed-crop species reflectance differences were generally greater at the 0.85 μm WL in the near-infrared spectral region than at the 0.55 μm WL in the visible region, indicating that color infrared (CIR) aerial photography may be useful to detect weed populations in crops. Canopy reflectance data were more directly related to photographic differences in weed-crop images than were single leaf or inflorescence reflectance data. Aerial photography at altitudes of 610 to 3050 m distinguished climbing milkweed (Sarcostemma cyancboides ♯ SAZCY) in orange [Citrus sinensis (L.) Osbeck. ‘Valencia’) trees; ragweed parthenium (Parthenium hysterophorus L. ♯ PTNHY) in carrot (Daucus carota L., var. sativa ‘Long Imperator’); johnsongrass [Sorghum halepense (L.) Pers. ♯ SORHA) in cotton (Gossypium hirsutum L. ‘CP 3774’) and in sorghum (Sorghum bicolor L. Moench. ‘Oro’); London rocket (Sisymbrium irio L. ♯ SSYIR) in cabbage; and Palmer amaranth (Amaranthus palmeri S. Wats. ♯ AMAPA) in cotton. Johnsongrass was also detectable with CIR film in maturing grain sorghum from 18 290 m. Detection of weed species in crops was aided by differential stages of inflorescence and senescence, and by the chlorophyll content, color, area, intercellular space, and surface characteristics of the leaves. Discrete plant community areas were determined by computer-based image analyses from a 1:8000-scale positive transparency with the efficiency of 82, 81, 68, and 100% for Palmer amaranth, johnsongrass, sorghum, and cotton, respectively. The computer analyses should permit discrete aerial surveys of weed-crop communities that are necessary for integrated crop management systems.