Oustar herbicide for efficient herbaceous weed control and enhanced loblolly pine seedling performance in the southeastern US

Oustar herbicide is a new pre-mixed blend of hexazinone (Velpar DF)+sulfometuron (Oust XP). Tests at six sites in the southeastern US were established to compare Oustar (0, 0.70, 0.91, 1.12, 1.33 kg of product per ha) to industry standards (Velpar L+Oust 2.34 + 0.14; Arsenal AC + Oust 0.29 + 0.14, both in L/ha + kg/ha) for herbaceous weed control (HWC) and resultant loblolly pine (Pinus taeda L.) seedling performance. Sites were prepared prior to planting with: fire only, chemical followed by a burn, mechanical only, or chemical and mechanical methods. Oustar (0.70 kg) and industry standards provided similar HWC and seedling performance. When averaged across all six sites, herbicide plots consistently had more bareground than untreated plots by nearly 2× at 30 days after treatment (DAT), 3× at 60 DAT, 4× at 90 DAT, and 5× at 120 DAT. Similarly, herbicide treatments increased age-two seedling survival (9%), total height (0.21 m), ground line diameter (0.66 cm), and volume index (0.44 dm3) over that of untreated seedlings. Late (October) site preparation commonly resulted in less herbaceous cover on application day. Sites with less ground cover on application day exhibited more bareground at 60 and 120 DAT than sites with high initial ground cover. The low rate (0.70 kg) of Oustar applied to sandy loam soils receiving chemical and mechanical preparation prior to planting provided bareground comparable to industry standards. Managers integrating late site preparation followed by spring HWC may achieve customary levels of HWC for more of the growing season with less herbicide than industry standards. Site preparation by HWC interactions reported for loblolly pine may have broader applications to coniferous plantation establishment. More research is needed to define additional site preparation by HWC interactions and their usefulness in coniferous plantation establishment. No adverse herbicide effects were seen on any crop trees.