Chemical Site Preparation Mixtures, Application Timing, and Herbaceous Weed Control Impacts on Loblolly Pine Development Through Six Years

Chemical site preparation is a critical management practice for southern pine plantation establishment. Imazapyr and ester triclopyr are frequently used for chemical site preparation in the Lower Coastal Plain to control waxy leaf shrub species, yet limited information is available on optimal imazapyr and triclopyr tank mixes and individual herbicide application timing(s) to achieve maximum loblolly pine (Pinus taeda L.) growth. The objectives of this study were to determine the survival, growth, and stem defect response of 6-year-old loblolly pine to four chemical site preparation treatments plus an untreated control, three application timings, and first year herbaceous weed control (hwc) on a poorly drained flatwoods site. Treatments included two imazapyr and triclopyr rates applied as tank mixes, triclopyr and imazapyr alone, and an untreated control with hwc applied to half of each treatment plot. Results showed no treatment had superior survival or growth, whereas September-applied imazapyr and triclopyr tank mixes tended to result in improved growth. Triclopyr alone along with first year, banded hwc resulted in similar growth to imazapyr and triclopyr tank mixes. First-year hwc significantly enhanced survival and growth. Stem defects were more common in the chemical site preparation treatments than the control. Study Implications: Age-6-year results from this study indicate that loblolly pine (Pinus taeda L.) growth following application of chemical site preparation tank mixes containing imazapyr and triclopyr applied during September or October tended to be superior to July applications. Triclopyr applied alone with first growing season herbaceous weed control (hwc) may offer satisfactory near- and long-term loblolly pine growth as imazapyr and triclopyr tank mixtures on sites with similar competing vegetation. These findings may allow for less herbicide use on sites previously managed for pine production and show the importance of first year hwc for Coastal Plain flatwoods sites.