investigation the effect of water hardness on 2,4-d amine efficacy on redroot pigweed (amaranthus retroflexous) and common lambsquart (chenopodium album) control

abstract water is the most common carier used to dilute herbicides and their application. researches had shown that water quality is an important factor in some herbicide efficacy. in order to study the effect of water hardness on 2,4-d efficacy, an experiment was carried out under controlled conditions in 2010 at the college of agriculture, ferdowsi university of mashhad. experimental treatments included herbicides doses at 6 levels (0, 1000, 1250, 1500, 1750 and 2000 ml ha-1 ), calcium carbonate concentration in water as index of water hardness at 6 levels( 0, 100, 300, 600, 1000 and 1500 ppm) and weeds at 2 levels ( redroot pigweed and common lamsquarter), were evaluated as a completely randomized design in a factorial arrangement with three replications. spray was done at 6-8 weeds leaf stage and two weeks after spray weeds survival and shoot dry matter was measured. for results analysis, data analysis of variance was done and plants response to 2,4-d doses in deferent water hardness levels was fitted with 4 parametric sigmoidal equation to the shoot biomass data as a function of the herbicide doses and was used to calculate the herbicide dose for 50 % inhibition of plants shoot growth inhibition (id50). results showed herbicide rate and water hardness had significantly effect(p<0.01) on growth and survival of two weeds. increasing herbicide doses, decreased the survival and growth of both weeds in pure water spraying. increasing water hardness decreased 2,4-d efficacy in both weeds. maximum (79.4 % , 91.7 %) and minimum (35.5 % , 74.3 %) shoot biomass lose were indicated at the highest and lowest levels of 2,4-d and calcium carbonate levels in common lambsquart and redroot pigweed respectively. redroot pigweed was more susceptible to 2,4-d application in each level of water hardness . increasing of water hardness, increased id50 parameter in both weeds. minimum (1057 ml ha-1) and maximum(2783 ml ha-1) 2,4-d id50 for common lambquart indicated in distilled water and 1000 ppm of calcium carbonate concentration. minimum (559 ml ha-1) and maximum(1270 ml ha-1) 2,4-d id50 for redroot pigweed was observed in 100 and 1500 ppm of water hardness.