Effect of Hexazinone Rate and Formulation on Loblolly Pine in Broadcast Release Applications

Abstract

Abstract Growth response and mortality of loblolly pine were examined 5 or 6 years after broadcast applications of four rates of pellet and liquid (applied as a foliar spray) hexazinone formulations for pine release at seven locations across the South varying in soil characteristics. Adjusted hardwood rootstock density 2 years following treatment was significantly affected by treatment and rate at all locations, and by formulation at five of the seven locations. Pine mortality was positively related to hexazinone rate at four of the study locations. Mortality was significantly higher for the pellet formulation compared to the liquid at the two locations with loamy sand surface soils. Mortality averaged less than 10% for the prescribed rate of both formulations at five of the seven locations, and at a sixth location for the pellet formulation. Mean pine height and dbh responses across hexazinone rates were greater than no treatment (check) at three and five locations, respectively. Response in dbh was positively related to hexazinone rate at three locations, and inversely related to rootstock density 2 years after treatment at six of seven locations. Mean treatment response for pine basal area and total volume (outside bark) per acre were significantly greater than the check at only two locations due to high pine mortality at some locations for 1.4X and 2.0X the prescribed rate. Mean increases in volume of the prescribed rate over the check were 9 and 7% for the pellet and liquid formulations, respectively. Maximum volume production increases across locations were 13% for the pellet formulation and 15% for the liquid formulation. South J. Appl. For. 15(1):54-61.