Basal Streamline Sprays for Hardwood Resprout Control: Herbicides, Concentrations,and Streaks

Intensive vegetation management alters seedling growth and development in southcm pine plantations. Adequate light, moisture. and nutrients stimulate seedling stem growth and crown development. Thus rapid stem growth could deplete nutrient and energy resources required for aggressive rcot growth. Early root system expansion within the available rooting zone is critical because structural root growth culminates in the early stages of plantation development. In 1995, a study was established at the Louisiana State University Lee Memorial Forest to determine the impact of rapid seedling stem growth on root system expansion in young southern pine plantations. The experimental area was a I2 ha pasture. Four southern pine species, loblolly pine (Pinus foe&), slash pine (Pinus ellioflii), shortleaf pine (Pinus echinaru), and ionglcafpine (finrrspalus~ris) were planted in separate 3 ha plantations at a spacing of 2.4m X 3.6m. Each plantation was divided into sis 0.5 ha plots. Two herbaceous weed suppression treatrncnts, no weed suppression (NWS) and single growing season weect suppression (WS). were assigned in a randomized complete block design and replicated three times. Predominant herbaceous species were bahiagrass (Paspalum no~otunr), vaseygrass (Paspalum urvillei), broomsedge (Andropogon virginicus), and maypop passionflower (Pass~jlom incomafu). Weed suppression treatment was a I .8m wide band cent& over the seedling row Aith season long suppression maintained by applying suifometuron at i40g/ha in April, whosate as a directed spray in June, and mctsulfuron at 7Og/ha in July. Seedling height and groundline diameter (GLD) were taken immediately after planting and at the end of the first growing season. In February, 1996, nine seedlings were excavated from each pint species/weed suppression treatment combination. Each seedling was separated into four components, stem, foliage, tap root, and lateral roots. and green and oven-dry weights determined for each component Except for longleafpine, WS treatment increased seedling stem growth. Height growth increases were detected for loblolly and shortleaf. averaging i33mm and 72rnm, and GLD increases were detected for lobloiiy, shortleaf, and slash, averaging 5rnm, 4mm, and 5mm. Total oven-dty stem biomass for all pine species difkred between treatments with the WS treatment being at least two times greater than the NWS. For both treatments and all species, the foliage component biomass exceeded the stem component by 66%. WS treatment total oven-dry root biomass exceeded NWS by at least two times. Although both WS treatment tap and lateral roo: biomass were greater than NWS treatment, biomass distribution between the two components differed among species. Shortleaf lateral root biomass exceeded tap root biomass, longleaf tap root biomass exceeded lateral root biomass, and loblolly tap and lateral root biomass did not differ. Slash pine root biomass distribution differed between treatments, lateral root biomass exceeding tap root in the WS treatment. Root/shoot ratio comparisons, which differed among species, indicated that intensive vegetation management did not alter seedling nourishment distribution patterns during the first growing season. Respective loblolly, shortleaf, slash, and longleaf root/shoot ratios were 20,26. 39. and 47% for the WS treatmentr and 20.22.38. and 47% for the NWS treatment. Afkr one growing season, rapid stem growth did not preferentially diminish root system growth and expansion.