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Hexazinone, applied as spheres or pellets (1.27 cm in diameter) in grid patterns (1.5 or 3 m spacings) at 2 or 4 kg/ha effectively controlled post oak and blackjack oak in east central Texas. The herbicide also appeared promising for control of water oak, American elm, and downy hawthome. Willow baccharis and winged elm appeared to be moderately susceptible to 2 kg/ha of the herbicide and w_ere controlled by 4 kg/ha. Yaupon canopies were initially reduced by the herbicide but had begun to recover by the second or third growing season after application and replaced the oaks as the primary limitation to range improvement following treatment, regardless of hexazinone rate applied. Saw greenbrier, mustang grape, southern dewberry, American beautyberry, and woollybucket bumelia were not controlled by hexazinone. The Post Oak Savannah occupies about 3.4 million hectares of gently rolling to hilly lands in east central Texas (Gould 1969). The grasslands of the Post Oak Savannah are well suited to livestock production, and optimum use for much of the area is as range if improved and properly managed (Scifres 1980). Much of the Post Oak Savannah has been converted from true Savannah to heavy thickets to woody plants, persumably the results of long-term overgrazing and the restriction of naturallyoccurring fires. Large post oak (Quercus stelluta) and blackjack oak (Quercus marilundicu) trees usually form the overstory above almost impenetrable thickets of yaupon (I/ex vomitoria), winged elm (Ulmus alata), woollybucket bumelia (Bumelia lanuginosa), downy hawthorne (Crategus mollis), spiny hackberry (Celtis pallida), common honeylocust (Gleditsia triacanthos), buckbrush (Symphroicarpos orbiculatus), tree huckleberry (Vaccinium arboreum) and other shrubs. The woody canopy of thicketized Post Oak Savannah restricts the growth of grasses except for the most shade-tolerant species such as low-growing dichantheliums (Dichanthelium spp.) and longleaf chasmanthium (Chasmanthium lati&olium). Soils of the Post Oak Savannah, typically fine sandy loams to loamy sands 20 to 70 cm thick over a claypan, are capable of supporting productive stands of grasses such as little bluestem (Schizachyrium scoparium var. frequens), Indiangrass (Sorghastrum nutans), switchgrass (Panicum virgatum), purpletop (Tridensflavus), and silver blueAuthor is professor, Department of Range Science (Texas Agricultural Experiment Station), Texas A&M University, College Station, 77801. Published with approval of the Director, Texas Agricultural Experiment Station as TA-16234. The author is grateful to Julia Scifres for manuscript typing and preparation. JOURNAL OF RANGE MANAGEMENT 35(3), May 1982 stem (Bothriochloa saccharoides) if effective brush management is practiced (Scifres and Haas 1974). However, costs of mechanical brush control methods usually restrict their application to complete conversion of these sites to tame pastures or cropland. Broadcast application of a mixture of 2,4,5-T[(2,4,5-trichlorophenoxy)acetic acid] and picloram (3,5,6-trichloropicolinic acid) effectively controls many of the woody species in the mixed-brush stands (Scifres and Haas 1974) but the proximity of herbicidesusceptible crops and vegetables seriously limits the use of aerial sprays in the region (Scifres 1980). Therefore, recent research interest has focused upon the development of dry herbicide formulations which minimize the potential of herbicide damage to adjacent, nontarget plants. Hexazinone [2-cyclohexy&(dimethylamino)l-methyl-l ,3,5triazine-2,4 (1 H, 3H-dione)] has shown promise for controlling several woody species on rangeland (Scifres and Mutz 1978), especially when applied as pellets (3.2 mm in diameter) in rows 1.8 m apart rather than broadcast (Meyer and Bovey 1980). Hexazinone is also applied as relatively large ( 1.27 cm diameter) spheres, and at wide but regular spacings so that herbaceous vegetation is damaged only in small, localized areas. This “grid placement” of herbicide has been used for applying karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxyphenyl)-l,l-dimethylurea] to achieve selective brush control (Scifres et al. 1978). The objective of this research was to evaluate the efficacy of hexazinone applied as relatively large spheres or pellets by grid placement for control of several woody species common to the Post Oak Savannah. Materials and Methods Hexazinone was formulated as compressed spheres or extruded pellets, 1.27 cm in diameter and containing 15% active ingredient. A random sample of 100 particles was weighed, and the grid spacings were calculated to achieve selected application rates. One experiment was installed on the Texas A&M University Range Research Area near College Station on March 24, 1976. Soil was of the Lufkin-Tabor series (Udertic Paleustalfs). The area supported a relatively open stand of post oak and blackjack oak in association with winged elm, woollybucket bumelia, water oak (Quercus nigra) and lesser amounts of various other woody species. The herbaceous understory was dominated by low-growing dichantheliums, brownseed paspalum (Paspalum plicatulum) and various forbs. Plots were 30by 30-m in size and separated by

Woody Plant Control in the Post Oak Savannah of Texas with Hexazinone