COMPARISON OF DURATION AND METHOD OF HERBACEOUS WEED-CONTROL ON LOBLOLLY-PINE RESPONSE THROUGH MIDROTATION

Herbaceous weed control studies installed by the Auburn University Sil vicultural Herbicide Cooperative to examine response to methods and du ration of herbaceous weed control in eight loblolly pine (Pinus taeda L.) plantations were analyzed to determine stand response through age 9. Studies were designed to compare weed control treatments with an un treated check, weed control methods (band vs. broadcast), and weed con trol duration (first year vs. first 2 years). Pine growth was increase d by weed control on all sites. Growth was increased by an additional year of weed control (duration) on about one-half of the sites, but di d not differ between band and broadcast treatments (method). Age 9 vol ume response above the check averaged 27.3 m3/ha for first-year weed c ontrol and 42.9 m3/ha for the first 2 years of weed control. Individua l-tree height growth between ages 7 and 9 did not differ by treatment at most sites, but stand volume growth was higher with weed control at six of the eight sites. Uniformity of individual tree size, as repres ented by the standard deviation of DBH adjusted for dominant height, w as more dependent on survival, hardwood encroachment, and level of fus iform rust stem infection, which varied by treatment and site, than on the result of herbaceous weed control per se. Growth projections made with the least intensive weed control treatment at each site indicate d that on average, merchantable volume at age 22 with weed control wil l equal that of an age 25 stand without weed control. Largest gains we re on sites where weed control increased survival.