INFLUENCE OF TEMPERATURE ON PHYTOTOXICITY OF TRIAZINE HERBICIDES TO PINE SEEDLINGS

Abstract

The effects of temperature, over a range of 5 to 30 C, on phytotoxicity of simazine, atrazine, propazine, prometryne, prometone, and ipazine to young Pinus resinosa seedlings were investigated in growth chambers. Herbicides were applied to the soil surface and then mixed into the soil before pine seeds were planted. Development of recently germinated seedlings was then studied for 7 weeks. High temperatures greatly accelerated herbicide toxicity, but the effects of temperature varied greatly among herbicides. Atrazine and simazine were more toxic than other herbicides tested at all temperatures. Toxicity of simazine and atrazine was apparent early, whereas effects of propazine, prometryne, prometone, and ipazine were somewhat delayed. After 7 weeks maximum dry‐weight production of shoots under each herbicide treatment and control occurred at 20 C, with some decreases noted at lower temperatures and marked decreases at progressively higher ones. At 20 C final seedling dry weights following treatment with simazine or atrazine were only one‐third as high as in control plants. Growth was also reduced in lesser amounts by propazine, prometryne, prometone, or ipazine. Variations in phytotoxicity of different triazine herbicides appeared to be related more to their structural differences than their solubilities. Under the constant environmental conditions of the experiments, toxicity symptoms in plants treated with triazine herbicides appeared more rapidly and decisively than in previous field experiments under fluctuating environments. The influence of high temperatures in enhancing triazine toxicity appeared to involve complex interactions of physiological activity of plants and temperature effects on herbicide uptake.