Toxicity of selected synthetic auxines - 2,4-D and MCPA derivatives to broad-leaved and cereal plants

MCPA, 2,4-D and their salts, amines or esters have been the most widely used herbicides for many years, especially in cereal crops. They kill broad-leaved plants but not grasses. These phenoxyherbicides have been detected in soil in concentrations reaching 0.63 mg/kg of dry matter. The present work was undertaken in order to study the toxicological effects of commercial preparations: Aminopielik 720 (2,4-D-NH4+ salt, 68% of active ingredient) and Chwastox Extra 300SL (MCPA-Na salt, 30% of active ingredient) on vascular plants. The species tested were the broad-leaved plants Lepidium sativum, Sinapis alba and grasses (cereal plants) Avena sativa, Triticum aestivium The influence of the commercial products on seed germination and root or shoot growth inhibition of the plants was studied. The tests lasted 168 h. Comparison of the IC50 values for the seed germination and shoot growth inhibition of grasses and broad-leaved plants showed great differences. IC50 values obtained for L. sativitm and S. alba were in some cases nearly 100 times lower than the IC50 values for A. sativa and T. aestivian (both in seed germination and shoot inhibition tests). In the case of root growth inhibition, the differences between IC50 values for broad-leaved plants and grasses were less significant for Chwastox Extra. The IC50 values for germination were very high (ranged from 104 to 6704 mg(a,i) 1(-1)), but for shoot (S) or root (R) growth inhibition they were lower and ranged from 0.15 to 73 mg(a.i.) 1(-1) (S) and from 0.07 to 12 mg(a.i.) 1(-1) (R) for broad-leaved plants and grasses, respectively. Thus phenoxyacetic herbicides have been found to inhibit root and shoot growth for both broad-leaved plants and grasses. (C) 2003 Elsevier Science Ltd. All rights reserved.