Herbicides 4-amino-3,5,6-trichloropicolinic acid (picloram) and 5-bromo-3-sec-butyl-6-methyluracil (bromacil) effectively controlled live oak (Quercus virginiana Mill.) when applied in the spring and fall in south Texas. A mixture of picloram plus (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) also was effective. Higher rates of bromacil were required than for picloram or picloram plus 2,4,5-T for effective control. Bromacil was more injurious to herbaceous vegetation. The phenoxy herbicides (2,4-dichlorophenoxy)acetic acid (2,4-D) and 2,4,5-T were ineffective.

Early spring spray applications of the potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram) and certain formulations of 1:1 mixtures of picloram plus (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) controlled yaupon (Ilex vomitoria Ait.). Ester formulations of picloram or picloram plus 2,4,5-T were ineffective. Combinations of surfactant and oil: water carriers usually did not improve herbicide performance over water carriers. Granular picloram was superior to sprays when applied as soil treatments at equal rates and controlled yaupon at most dates of application. Post oak (Quercus stellata Wangenh.) and blackjack oak (Quercus marilandica Muenchh.) were controlled more effectively by picloram or picloram plus 2,4,5-T sprays on the foliage than by granular picloram as a soil treatment. Picloram granules usually killed winged elm (Ulmus alata Michx.) regardless of date of application.

We compared foliage sprays of (2,4-dichlorophenoxy)acetic acid (2,4-D) and 4-amino-3,5,6-trichloropicolinic acid (picloram) for control of Macartney rose (Rosa bracteata Wendl.) applied with ground equipment and airplane. Picloram at 0.5 lb/A was more effective than 2,4-D at 2 lb/A at all dates of application on mowed roses; however, time of application was important. Picloram was most effective in late April and early May, but 2,4-D was most effective in late May and early June. Combinations of picloram and 2,4-D were effective from late April to late June. If mowing is followed by foliage treatment of 2,4-D, the interval between mowing and spraying should be at least 1 year if mowing is done in the spring. The interval between mowing and spraying was not critical when picloram was applied not later than early May. Mowing in the summer reduced the effectiveness of subsequent 2,4-D and picloram treatments applied the following year. Aerial applications of 2,4-D and picloram on undisturbed Macartney rose plants in the fall were not as effective as spring applications; however, two successive fall applications of picloram at 1 lb/A resulted in control equivalent to that obtained with a single 2 lb/A application in spring.

Granular 4-amino-3,5,6-trichloropicolinic acid (picloram) was effective in controlling live oak (Quercus virginiana (Mill.), huisache) (Acacia farnesiana (L.), Willd.), and yaupon (Ilex vomitoria Ait.), but not honey mesquite (Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell) in south Texas. Granular 5-bromo-3-sec-butyl-6-methyluracil (bromacil) controlled live oak and huisache. Herbicides applied to soil were usually most effective in spring and fall during periods of active brush growth. Picloram granules applied in May to a mixed stand of woody plants in Puerto Rico usually were effective. However, rates up to 30 lb/A were ineffective on some species.

We applied (2,4-dichlorophenoxy)acetic acid (2,4-D), (2, 4,5-trichlorophenoxy)acetic acid (2,4,5-T), 4-amino-3,5,6-trichloropicolinic acid (picloram), and 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) alone and in various combinations by aircraft on arborescent species in Texas and Puerto Rico. Paraquat defoliated trees rapidly but did not give long-term control. Picloram defoliated a greater number of species than the other herbicides and defoliation extended over a longer period. No treatment killed all trees in the mixed forest or prevented regrowth and secondary succession for a period of more than 1 year. Higher herbicide rates were necessary to defoliate woody plants in tropical Puerto Rico than in subtropical Texas.

We studied 4-amino-3,5,6-trichloropicolinic acid (picloram) alone and in combination with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) or 1,1′-dimethyl-4,4′-bipyridinium salt (paraquat) for control of several greenhouse, nursery, and natural-grown, woody plant species. Picloram:paraquat combinations improved the control of some species such as yaupon (Ilex vomitoria Ait.) as compared to picloram alone at equal rates; but it had an antagonistic effect on huisache (Acacia farnesiana (L.) Willd.) and honey mesquite (Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell). Evaluation of picloram: 2,4,5-T combinations suggested that 2,4,5-T sometimes could be added in equal amounts to picloram to increase control or reduce picloram rates proportionately on huisache, honey mesquite and live oak (Quercus virginiana Mill.).