Root growth potential and weed control effects on the first year growth of pitch x loblolly pine (Pinus ridiga x P. taeda L.) and loblolly pine

The study was initiated to determine the effects of RGP and three levels on weed control: no weed control (control), herbaceous weed control (Oust), and woody and herbaceous weed control (Oust-Garlon) on three pine seedlots: pitch x loblolly pine hybrid (pxL-F2), Virginia Department of Forestry loblolly pine (VDF-Iob), and westvaco loblolly pine (WCO-Iob).

Lateral roots had the greatest response to the Oust treatment compared to all other seedling parts. All seedlot and treatment interactions were associated with lateral roots. After one growing season the Oust treatment resulted in a 148% increase in lateral root biomass compared to the control treatment. Shoot biomass in the Oust treatment increased by 70% compared to the control.

The ability to respond to weed control was related to RGP. Compared the loblolly pine seedlots the PxL-F2 had both significant higher RGP at planting and biomass accumulation in response to the Oust treatment. Compared to the loblolly pine seedlots the PxL-F2 lateral root biomass and total tree biomass increased by 44% and 30%, respectively.

The addition of woody weed control to herbaceous weed control in the Oust-Garlon treatment did not result in significant increasings in loblolly pine seedling biomass compared to herbaceous weed control. Because of a to sensitivity to Garlon 4™ the (PxL-F2) had 22% reduction in total tree biomass in the Oust-Garlon treatment compared to the Oust treatment. Therefore, the control of woody weeds in pitch x loblolly pine plantations will need to be accomplished using another herbicide.