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.

Twenty herbicides were applied to a rangeland pasture in the Post Oak Savannah Resource Area of Texas in April 1978 and May 1979. At time of treatment, total vegetation cover was 88 to 100%, with 36% grasses and 52 to 64% broadleaf cover. From May 31 through September, total, grass, and broadleaf covers were 89 to 100, 51 to 65, and 27 to 44%, respectively. One to 2 months after treatment, grass cover generally increased except where certain herbicides, particularly bromacil (5-bromo-3-sec-butyl-6-methyluracil), dalapon (2,2-dichloropropionic acid), glyphosate [N-(phosphonomethyl)glycine], or hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4 (1H, 3H)-dione] had been applied. By September or October in the year of application only dalapon consistently reduced grass cover. In the year following treatment, grass cover was still reduced on the dalapon-treated plots. Most herbicides reduced broadleaf cover in the year of treatment. Broadleaf cover returned most rapidly to those areas treated with dalapon. During the year following treatment, broadleaf cover remained low on plots treated with picloram (4-amino-3,5,6-trichloropicolinic acid), 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and picloram + 2,4,5-T. For plots treated in 1978, the grass and broadleaf standing-crop weights of untreated plots were 490 and 450 kg/ha, respectively, in October 1978, and 2707 and 1033 kg/ha in October 1979. In 1978, grass weight increased with several herbicide treatments whereas only dalapon increased the broadleaf weight. For plots treated in May 1979 and harvested in September 1979, grass and broadleaf standing-crop weights of untreated plots were 2629 and 607 kg/ha, respectively.

Live oak (Quercus virginiana Mill. # QUEVM) on the Texas Coastal Prairie was treated with herbicides using ground and aerial application methods. Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} and pellets of buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} at 2.2 kg ai/ha were the most effective herbicides, killing 60 to 95% of the live oak. Tebuthiuron pellets 3.2 mm in diam were more effective than the wettable powder at 1.1 kg/ha. Bay Met 1486 {N-[5-(ethylsulfonyl)-1,3,4-thiadiazole-2-yl]-N,N′-dimethylurea}, Dowco 290 (3,6-dichloropicolinic acid), hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H, 3H)-dione], and picloram (4-amino-3,5,6-trichloropicolinic acid) reduced the live oak canopy at 2.2 kg/ha whereas 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} were ineffective. Foliage-active herbicides generally were most effective in reducing the live oak canopy during the year of application. The soil-active herbicides generally were most active 1 or 2 yr after herbicide application. All herbicides reduced the live oak cover sufficiently to allow an increase in grass cover 2 to 4 months after treatment. Tebuthiuron at 2.2 kg/ha maintained a high degree of grass cover at least 2 or 3 yr after treatment.

Under unsaturated-flow conditions, bromacil (5-bromo-3-sec-butyl-6-methyluracil) was considerably more mobile than buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxyl-1-methyl-2-imidazolidinone}. Because of their high water solubilities, both herbicides were much more mobile than atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), prometon [2,4-bis (isopropylamino)-6-methoxy-s-triazine], or diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. Under saturated-flow conditions, buthidazole was leached through Lakeland loamy sand in slightly greater amounts than tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} or CN-10-3510 (formerly VEL 3510) {1-β,β-dimethoxyl-1-methyl-3-[5-(1,1-dimethylethyl)-1,3, 4-thiadiazol-2-yl] urea}. Distribution of the three herbicides in the leached soil was similar and relatively uniform. In Lakeland loamy sand, 30 times as much tebuthiuron was leached under saturated-flow conditions as under unsaturated-flow conditions. Intermittent saturated-unsaturated-flow conditions resulted in four times as much leaching of tebuthiuron as unsaturated flow alone. Only one-tenth as much tebuthiuron leached under intermittent saturated-unsaturated-flow conditions as under saturated-flow conditions. Tebuthiuron added to Lakeland soil and oven-dried was retained in significantly greater amounts than when added to moist Lakeland soil. Low amounts of tebuthiuron leached through Lakeland loamy sand, Portsmouth sandy loam, and Rains silt loam, but high amounts leached through Davidson clay. Greater amounts of the herbicide were retained in the surface zones of the three former soils, but the inverse was the case for the Davidson soil.

Yaupon (Ilex vomitoria Ait. ♯ ILEVO) in the Post Oak Savannah of Texas was treated with liquid and dry formulations of herbicides. Sprays of Bay Met 1486 {N-[5-(ethylsulfonyl)-1,3,4-thiadiazol-2-yl]-N, N′-dimethylurea} and picloram (4-amino-3,5,6-trichloropicolinic acid), sprays and pellets of tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and boluses of hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1N,3H)-dione] at 4.5 kg ae or ai/ha were the most effective treatments, reducing the canopy 87 to 99% and killing 68 to 93% of the yaupon after 2 yr. The percentage of dead yaupon after 1 yr was similar to that found 2 or 3 yr after treatment. Most herbicides, except clopyralid (3,6-dichloro-2-pyridinecarboxylic acid), reduced the yaupon canopy sufficiently to allow an increase in understory grass and broadleaf vegetation, particularly 1 yr after treatment.

Picloram (4-amino-3,5,6-trichloropicolinic acid) and tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} were the most effective herbicides for killing Macartney rose (Rosa bracteata Wendl.) on the Claypan Resource Area of Texas. At 4.5 kg/ha picloram (ae/ha) and tebuthiuron (ai/ha) as sprays killed 70% of the plants and as pellets 73 and 84% 1 yr after application, respectively. Bay Met 1486 {N-[5-(ethylsulfonyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone}, 2,4-D [(2,4-dichlorophenoxy) acetic acid], 3,6-dichloropicolinic acid, glyphosate [N-(phosphonomethyl)glycine], hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione], and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid} were markedly less effective than either picloram or tebuthiuron. After 2 to 4 months, 2,4-D, picloram, picloram + 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and triclopyr reduced the Macartney rose canopy by at least 95%, but only picloram and tebuthiuron controlled Macartney rose after 3 yr. Sprays of glyphosate and hexazinone inhibited growth of grasses after 3 months. Most herbicide sprays reduced broadleaf cover for at least 3 months.