THE SELECTIVE ACTION OF PICLORAM IN RED MAPLE AND WHITE ASH

Abstract

Summary. White ash (Fraxinus americana L.) trees, 2 years of age, treated continuously with 10 ppm picloram (4‐amino‐3,5,6‐trichloropicolinic acid) in nutrient culture were only slightly injured after 4 weeks whereas red maple (Acer rubrum L.) trees were killed after only 2 weeks treatment.When the roots were exposed to 10 ppm 14C‐picloram, the rate of root uptake, acropetal translocation in the stem, and accumulation in the leaves was much lower in the susceptible red maple than in the tolerant white ash. The foliar penetration and translocation of 14C‐picloram applied to the leaves was very slight but similar in both species. Although a radiolabelled picloram metabolite was isolated from plant extracts, it was formed at equal rates in both species.It was concluded that the tolerance of white ash was not related to lower rates of picloram uptake or faster rates of picloram detoxication. It was postulated that the high susceptibility of red maple was due to a blockage of the xylem by picloram which caused death by a dessication of the leaves and upper stems. Action sélective du piclorame sur Fraxinus amerieana L. et Acer rubrum L.