Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] applied as a preplant treatment at rates of 2.24 to 8.96 kg/ha was evaluated for the control of perennial grasses and the establishment of jeffrey (Pinus jeffreyi Grev. & Balf.) and ponderosa (Pinus ponderosa Laws.) pine transplants. The most consistent and effective rates of atrazine (6.72 and 8.96 kg/ha) reduced grass herbage biomass an average of 72% over a 3-yr period and increased average final survival of transplants from 1% on the control to 66% with treatment. These rates also gave continued grass control for at least 3 to 4 yr after treatment. Stem diameter and top growth tended to be greater on the most effective treatments. High survival and increased growth of transplants on these treatments were attributed to low soil moisture tensions and increased NO3-N accumulation throughout the summer to depths of 30 cm during the year of planting and subsequent years.
