Leaves absorbed high amounts of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) as foliar sprays on honey mesquite (Prosopis glandulosa Torr. # PRCJG) as indicated by concentrations of 10 μg/g fresh wt or more in basal stem phloem by 4 days after treatment. Small quantities of clopyralid (< 1 μg/g) were detected in basal stem phloem after spray applications of clopyralid to defoliated plants or roots treated by soil application. When applied to foliated plants, the 0.56 kg/ha of clopyralid killed 60% or more plants, but none were killed when clopyralid sprays were applied to defoliated plants or when 2.2 kg/ha of clopyralid was applied to the soil. Water, diesel oil plus water, or water plus surfactant were equally effective as clopyralid carriers as foliar sprays.

Economic performance of prescribed burning following aerial applications of tebuthiuron {N-[5-(1,1-dimethyiethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} pellets was estimated for Texas whitebrush (Aloysia gratissima [Gillies & Hook.] Troncoso # ALYLY)-dominated rangeland and for post oak (Quercus stellata Wangenh. # QUESL)-dominated mixed hardwood stands. Honey mesquite (Prosopis glandulosa Torr. # PRCJG) invasion largely negated differences in estimated beef production between treated and untreated pastures within 13 yr of controlling Texas whitebrush with tebuthiuron at 2 kg ai/ha. American beautyberry (Callicarpa americana L.) and other shrubs increased such that the woody canopy cover was 87% of the original canopy 7 yr after applying tebuthiuron at 2.2 kg/ha to a heavy cover of oaks-mixed hardwoods. Burning at 2- to 4-yr intervals after tebuthiuron applications suppressed invading shrubs and increased projected internal rates of return by about 2% for each burning, compared to herbicide application only.

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.

Honey mesquite (Prosopis glandulosa Torr. # PRCJG) was treated with four herbicides at 1.1 kg ae/ha at 14 dates from April 30 through September 23 over a 2-yr period. Overall, clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) was the most effective herbicide, killing 80% or more of the honey mesquite at most dates. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] were less effective than clopyralid. Honey mesquite control was correlated with Julian day of year sprayed, 15 plant, 11 environmental, and 8 herbicide concentration variables. Most effective control was negatively correlated with Julian day of year sprayed and new xylem ring thickness. Control was positively correlated with total daily apparent photosynthesis, upward methylene blue dye movement in the xylem, and herbicide concentration in the xylem 3 days after spraying. The only environmental variable of 11 measured that was significantly correlated with honey mesquite control was soil water and that was only with picloram. The concentration of herbicide in the stem was highest for clopyralid, followed by picloram, and then by 2,4,5-T and triclopyr, which were about equal. Variables most useful in regression equations for predicting control with herbicides were total daily apparent photosynthesis and rate of upward movement of methylene blue dye. Variables most incorporated into regression equations relating honey mesquite control with herbicide content were herbicide concentrations in the xylem 3 or 30 days after treatment.

The addition of surfactant (trimethylnonylpolyethoxyethanol) at 0.5% (v/v) of the spray solution caused a twofold increase in the deposit of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) applied at 0.14 or 0.28 kg ae/ha on greenhouse-grown honey mesquite (Prosopis glandulosa Torr. # PRCJG) and increased transport into the plants compared to clopyralid applied alone. Application of equal rates of benazolin [4-chloro-2-oxo-3(2H)-benzothiazoleacetic acid] with clopyralid at 0.28 + 0.28 kg/ha enhanced transport of clopyralid into honey mesquite. Spray deposit, absorption, and translocation of clopyralid was unaffected by addition of 0.5% (v/v) of d'limonene (4-isopropenyl-1-methyl-cyclohexane). Greater spray deposit of clopyralid on plant surfaces after addition of surfactant was associated with reduced liquid surface tension and greater percentage of spray volume in small droplets (<204-μm diam).

Greenhouse experiments were conducted to assess the storage of nonstructural carbohydrates in the stems and roots of honey mesquite and their mobilization and utilization following defoliation by hand or clopyralid. All leaves were removed by hand from one group of plants while leaving stems intact. Another group received a foliar spray of clopyralid at a sublethal acid equivalent rate of 0.07 kg ha−1. Samplings at treatment on day 0 and at 14, 28, 42, and 58 d after treatment measured leaf area; dry weight of leaves, stems, and roots; and grams and percent total nonstructural carbohydrates in stems and roots. Controls accumulated dry weight and grams total nonstructural carbohydrates in stems and roots, while maintaining a constant percent total nonstructural carbohydrates throughout the experiment. Percent and grams total nonstructural carbohydrates in stems and roots of hand defoliated plants decreased by about one-half from day 0 to 14 as new leaf growth occurred, but increased and returned to pretreatment levels on day 28. A similiar, though slower, pattern of decline and recovery of total nonstructural carbohydrates in stems and roots occurred in response to defoliation by clopyralid. These results showed that the nonstructural carbohydrates in stems and roots of honey mesquite were important sources of carbohydrates to support new leaf regrowth following defoliation by hand or herbicide.

Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), and clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were applied to honey mesquite (Prosopis glandulosa Torr. # PRCJG) on seven different dates about every 3 weeks from May to September in 1980 and 1981. Concentrations of 2,4,5-T or triclopyr in stem tissue were usually less than 2 μg/g fresh weight regardless of date of application. Concentrations of picloram and clopyralid were as high as 11 and 22 μg/g fresh weight, respectively, in upper stem phloem at some dates of application. Higher concentrations of all herbicides were detected in upper stem phloem than in the upper stem xylem or basal stem phloem or xylem. More herbicide tended to be detected in stems when herbicides were applied early (May and June) than late (August and September) in the season. Concentrations of triclopyr and picloram recovered from honey mesquite stems were about 25% greater at 3 than at 30 days after treatment, whereas concentrations of 2,4,5-T and clopyralid were about 50% greater at 3 than at 30 days after application.

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.

Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} was aerially applied at four locations in Texas to determine effectiveness of the amine and ester formulations for the control of honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell # PRCJG]. The ester formulation was superior to the amine in most trials. Honey mesquite control with triclopyr amine was comparable to that with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] while control with triclopyr ester was similar to that attained with a 1:1 mixture of 2,4, 5-T and picloram (4-amino-3,5,6-trichloropicolinic acid). Honey mesquite control obtained with a 1:1 mixture of 2,4,5-T and dicamba (3,6-dichloro-o-anisic acid) was intermediate between that with the 2,4,5-T and picloram mixture and that with 2,4,5-T alone. Efficacy of triclopyr increased as rates were increased from 0.3 to 0.6 kg ae/ha and from 0.6 to 1.1 kg/ha. Triclopyr formulations were effective when applied in either water or diesel oil/water emulsions. Honey mesquite control from triclopyr in combination with picloram was generally comparable to that from the mixture of picloram and 2,4,5-T.

Herbicide solutions of known concentration were applied to honey mesquite (Prosopis glandulosa Torr. # PROJG) with a tractor-mounted carpeted roller. The volume of solution applied was measured, and average height and density of the honey mesquite stands were also determined. The volume of solution applied ranged from about 3 to 20 L/ha and was positively correlated with stand density (r2 = 0.71). Height of the stand had no influence on volume of solution applied. Amounts of herbicide applied at concentrations of 30, 60, and 120 g/L averaged about 0.2, 0.6, and 1.25 kg ae/ha, respectively. Calculated amounts of active ingredient of herbicide applied to individual plants (dosage) ranged from 0.3 to more than 3 g/shrub and decreased curvilinearly with increasing stand density, suggesting that the carpeted roller is most efficient in treating sparse stands.

The objective of this study was to determine the effectiveness of tebuthiuron {N-[5-(1,1-dimethylethyl)- 1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} to treat brush-infested arid rangeland under field-scale conditions. A 130-ha tract in southern New Mexico dominated by creosotebush [Larrea tridentata (Sesse & Moc. ex DC.) Coville #3 LARTR) was treated with pelleted tebuthiuron at 0.4 kg ai/ha. After the fourth season following treatment, control of creosotebush, honey mesquite (Prosopis glandulosa Torr. #PRCJG), and tarbush (Flourensia cernua DC. # FLOCE) was 87, 48, and 100%, respectively. Total shrub density was reduced from 4440 plants/ha to 570 plants/ha. Grass basal area increased from 1.1 to 3.4%. The treatment did not affect forbs greatly. Total herbaceous above-ground biomass production in the fourth season after treatment was 860 kg/ha compared to 140 kg/ha on an adjacent untreated area. Perennial grass production was nearly 11-fold greater on the treated area than on the untreated area.

Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) was superior to 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], dicamba (3,6-dichloro-o-anisic acid), picloram (4-amino-3,5,6-trichloropicolinic acid), and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} for control of honey mesquite (Prosopis glandulosa Torr. ♯ PRCJG) in the field. However, equal ratio mixtures of clopyralid + picloram or triclopyr (0.28 + 0.28 or 0.56 + 0.56 kg ae/ha) were as effective for honey mesquite control as clopyralid at rates of 0.56 and 1.12 kg/ha. Equal mixtures of picloram + 2,4,5-T, picloram + triclopyr, picloram + dicamba, triclopyr + 2,4,5-T, or triclopyr + dicamba were less effective in controlling honey mesquite than clopyralid alone or clopyralid + picloram or triclopyr in 1:1 mixtures. In the greenhouse, mixtures of clopyralid + 2,4,5-T, picloram, or triclopyr were highly effective for the control of honey mesquite. Mixtures of 2,4,5-T + picloram, 2,4,5-T + triclopyr, or triclopyr + picloram were also effective when applied at 0.28 + 0.28 kg/ha.

Shin oak is a deciduous shrub that forms dense stands of brush on sandy soils in rangeland areas of the Rolling and High Plains of Texas. Plant canopy reflectance measurements made on shin oak showed that it had both low visible (0.63- to 0.69-μm waveband) and nearinfrared (0.76- to 0.90-μm waveband) reflectance values, a characteristic generally not shared by associated plant species or mixtures of species. The low reflectance values of shin oak caused it to have dark-red, reddish-brown, or brown image tones on color-infrared photographic, videographic, and SPOT satellite images that made it distinguishable from associated vegetation and other land use features. The optimum time to remotely distinguish this noxious shrub is during the mature phenological stage from June to September. Computer-based image analyses of video and satellite images showed that shin oak populations could be quantified. This technique can permit “percent land area” estimates of shin oak on rangelands. The aerial imagery is useful for detecting shin oak on smaller rangeland areas, whereas the satellite imagery is applicable in mapping large areas of shin oak distribution.

Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} at 2 or 4 ppmw placed 0 to 3, 8 to 11, or 15 to 18 cm deep in soil columns reduced root and shoot weights of buffelgrass [Pennisetum ciliare (L.) Link # PESCI] 30 days after emergence. Plains bristlegrass (Setaria macrostachya H.B.K.) seedling shoot weights were not reduced when 2 ppmw tebuthiuron was placed 8 to 11 cm deep or deeper. Effects of tebuthiuron at 0.13 to 0.50 ppmw on buffelgrass shoot and net tiller production were not moderated by the presence of honey mesquite (Prosopis glandulosa # PRCJG) in the pots. However, regardless of tebuthiuron dosage, average height and shoot weight of buffelgrass seedlings were greater when seedlings were grown in soil collected from beneath honey mesquite canopies compared to growth in soil from interspaces. Therefore, spatial variations in buffelgrass response to applications of tebuthiuron for control of invading shrubs may largely be attributed to soil changes induced by woody plants rather than to presence of shrubs.

Foliar sprays of the monoethanolamine salt, potassium salt, free acid, and 1-decyl ester of clopyralid were more effective in killing greenhouse-grown honey mesquite than the 2-ethylhexyl ester at rates of 0.28 ae/ha or less. More clopyralid was transported to the lower canopy from application of the monoethanolamine salt and potassium salt than the 2-ethylhexyl ester of clopyralid at 4 h or 1, 3, or 8 days after treatment. Application of the monoethanolamine salt and the 2-ethylhexyl ester to leaves with a pipet indicated that about twice as much clopyralid was absorbed within 15 min from the ester form (26%) than from the amine form (12%) of the total recovered. However, after 24 h, absorption of the ester was less than the amine. More than twice as much clopyralid was transported from the treated leaf after application of amine than the ester. Only the acid form of clopyralid was transported away from the site of application of either ester or amine.

Grid applications of hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] pellets at 2.2 kg ai/ha or less did not effectively control honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell ♯3 PRCJG], blackbrush acacia (Acacia rigidula Benth. ♯ ACARI), lotebush condalia [Condalia obtusifolia (Hook.) Weberb. ♯ CNCOF], granjeno (Celtis pallida Torr. ♯ CETPA) or twisted acacia [Acacia tortuosa (L.) Willd.] growing as mixed stands on clay loam or clay soils. Efficacy of hexazinone apparently was affected little by variation in rainfall ranging from 35% less to 51% greater than the long-term average during the year of application. Apparent mortality of honey mesquite, granjeno, and lotebush condalia was increased by increasing the application rate from 2.2 to 4.5 kg/ha on clay loam soils. Control of honey mesquite, blackbrush acacia, and twisted acacia with 2.2 kg/ha was better when applied to sandy clay loam than to clay soils.

Chlorsulfuron and metsulfuron were effective on Texas whitebrush, killing 70 to 75% of the plants at 0.28 kg ai ha, marginally effective on Macartney rose, killing 15 to 43% of the plants at 1.12 kg ha, but ineffective on honey mesquite and huisache, killing no more than 10% of the plants at 1.12 kg ha. Sulfometuron was ineffective on all woody species at 1.12 kg ai ha. Clopyralid and picloram were effective, killing 70 to 92% of the huisache at 2.24 kg ae ha. Tebuthiuron killed 72% of the Texas whitebrush at 1.12 kg ai ha. Sulfometuron generally reduced herbaceous plant cover the year of application. Chlorsulfuron and metsulfuron often resulted in increased grass cover the year of application. Most herbicides reduced broadleaf weeds the year of application. Woolly croton often was the first prominent broadleaf species to return to areas treated with clopyralid and sulfometuron. Few differences occurred among herbicides in herbaceous weed cover the year following treatment.

Greenhouse and field experiments were conducted to evaluate clopyralid formulations and triclopyr ester alone and in mixtures for control of honey mesquite. In the greenhouse the butoxyethyl ester of triclopyr enhanced activity of the monoethanolamine salt of clopyralid when applied as mixtures for total rates of 210 to 630 g ae ha-1. Greenhouse activity of triclopyr was not enhanced with the addition of clopyralid. In the field, 1989 applications of these same formulations, mixtures, and rates were usually synergistic, with each mixture killing more plants than the combined effect of either herbicide applied alone. For example, clopyralid plus triclopyr at 140 plus 140 g ae ha-1 killed 87% of the plants. When applied alone at 140 g ha-1 neither herbicide killed >27% of the plants. Honey mesquite response to the potassium or oleylamine salt of clopyralid was similar to the monoethanolamine salt when applied alone or in mixtures with triclopyr ester. Effectiveness of these mixtures in 1990 was similar to the 1988 and 1989 applications except that two to three times more herbicide was required for high mortality in 1990 because of unfavorable environment and plant growth prior to treatment.

Leaves of greenhouse-grown honey mesquite [Prosopis juliflora (Swartz) DC var. glandulosa (Torr.) Cockerell # PRCJG] initially absorbed more triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} from application of the ester than the amine salt. After 24 h, however, honey mesquite had absorbed 66% of the applied ester formulation and 72% of the amine formulation. Triclopyr was rapidly transported from the treated leaf to other plant parts. Triclopyr concentrations recovered 4 h after treatment in the upper canopy, lower canopy, and roots averaged 0.12, 0.19, and 0.09 μg, respectively. Concentrations of triclopyr recovered after 24 h were not significantly different than after 4 h in the canopy. No ester from ester application was recovered in the canopy, other than that in the treated leaf. Triclopyr recovered from stems of honey mesquite in the field ranged from 0.16 to 0.72 μg/g in phloem and from 0.04 to 0.20 μg/g in xylem from a broadcast spray application of the butoxyethanol ester at 1.12 kg/ha. Concentrations of triclopyr were usually not significantly different in either the upper or lower stems whether sampled 3 or 30 days after treatment.

Greenhouse and field experiments were conducted in east-central Texas to evaluate the influence of simulated rainfall on the availability of foliar-applied herbicides for huisache and honey mesquite control. The foliar activity of the amine salts of glyphosate, dicamba, picloram, clopyralid, and triclopyr was decreased on greenhouse-grown huisache when simulated rainfall was applied up to 240 min after herbicide treatment. The effectiveness of the butoxyethyl ester of triclopyr or 2,4,5-T was not reduced by rainfall washoff within 15 min after application. In natural huisache stands, injury from the ester of triclopyr or amine salts of picloram or clopyralid was not reduced by simulated rainfall at 60 min after herbicide treatment. In the greenhouse and field, honey mesquite leaves rapidly absorbed most herbicides, and triclopyr, 2,4,5-T, picloram, and clopyralid were highly phytotoxic even when simulated rainfall was applied within 15 min after herbicide treatment.