Blackbrush acacia and huisache, two troublesome woody legumes on Texas rangelands, could be distinguished on conventional color aerial video imagery. The integration of a global positioning system with the video imagery permitted latitude/longitude coordinates of blackbrush acacia and huisache infestations to be recorded on each image. Global positioning system coordinates were entered into a geographic information system to map blackbrush acacia and huisache populations over an extensive rangeland area.

Huisache [Acacia farnesiana (L.) Willd. # ACAFA] and Mexican palo-verde (Parkinsonia aculeata L. # PAKAC) are native woody legumes that often occur together on rangelands of southern Texas and northern Mexico. Huisache produces a profusion of orange-yellow flowers during February or March giving it a conspicuous golden appearance. Mexican palo-verde produces a heavy bloom of yellow flowers in mid-April or early May giving it a yellow-green coloration. Plant canopy light reflectance measurements of flowering huisache showed that its reflectance at the 0.55- and 0.65-μm visible wavelengths was significantly higher than that of Mexican palo-verde in the vegetative stage and four other associated plant species or mixture of species. Conversely, reflectance measurements of flowering Mexican palo-verde showed that its reflectance at the 0.55-μm visible wavelength was significantly higher than that of huisache in the vegetative stage and the same four associated plant species or mixtures of species. Flowering huisache had a golden color on conventional color (0.40-to 0.70-μm) aerial photos that made it distinguishable from other plant species, whereas flowering Mexican palo-verde had a pink image on color-infrared (0.50- to 0.90-μm) aerial photos. However, immature plants of both species cannot be detected using this technique. Computer-based image analyses of conventional color film positive transparencies showed that huisache infestations could be quantified from associated rangeland species. This technique can permit ‘percent land area infested’ estimates of mature huisache on rangelands. These results show that aerial photography may be a useful tool to detect and monitor the spread of huisache and Mexican palo-verde on rangelands, and to delineate areas needing control.

Mortality of potted huisache seedlings averaged 87 to 100% 18 weeks after picloram or clopyralid was applied with a model carpeted roller at concentrations as low as 7.5 g ae/L. A 1:1 mixture of picloram and clopyralid was equally effective. Triclopyr was effective only when applied to small seedlings in the spring, and an ester was more effective than an amine formulation. A 1:1 mixture of clopyralid and triclopyr ester was intermediate in effectiveness between the two herbicides applied alone. Adding surfactant increased canopy reduction and plant mortality (P = 0.1 to 0.01), especially at lower herbicide concentrations.

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 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.

Experiments were conducted in south Texas from 1983 to 1987 to evaluate clopyralid for huisache control using a carpeted roller. Huisache control with clopyralid applied as broadcast sprays or with a carpeted roller generally equaled that from the same rates of picloram or of 1:1 mixtures of clopyralid plus picloram. Applications of herbicides in the fall generally were more effective than in the spring, regardless of application method. In most cases, the herbicides at 48 to 60 g ae/L fall applied with a carpeted roller killed 70% or more of the huisache. Herbicide efficacy was not reduced when all huisache top growth was removed within 1 week after roller application of a 1:1 mixture of clopyralid and picloram at 60 g ae/L. The treat-and-cut sequence should improve the quality of hay from huisache-infested pastures.

Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} in various formulations and placements was applied to honey mesquite (Prosopis glandulosa Torr. # PRCJG), huisache [Acacia farnesiana (L.) Willd. # ACAFA], live oak (Quercus virginiana Mill. # QUEVI), Macartney rose (Rosa bracteata J. C. Wendl. # ROSBC), and Texas whitebrush [Aloysia gratissima (Gillies & Hook.) Troncoso # ALYLY]. There was little difference in a species response to the various tebuthiuron formulations. Pellets (20%) at 2 g ai/tree base reduced the canopy 85% and killed 50% of the honey mesquite. At 1 g ai/plant, two briquettes at 0.5 g ai each or pellets (5.14 g, 20%) killed 37 and 80% of the huisache, respectively. Pellets were no more effective at 2 g than at 1 g ai on huisache. Basal treatments of 0.25, 0.5, 0.5, 1, and 2 g ai tebuthiuron/tree killed from 8 to 22, 48 to 62, 62 to 85, and 92% of the live oak, respectively. Pellets at 2 g ai placed at the base reduced the canopy 83% and killed 59% of the Macartney rose. On Texas whitebrush, 0.25, 0.5, 1, and 2 g ai tebuthiuron/tree killed from 68 to 85, 75 to 100, 90, and 100% of the plants, respectively. Tebuthiuron persisted mainly in the upper 30 cm of soil for at least 15 months.