Hexazinone toxicity in red pine and jack pine

Abstract

Experiments were conducted under controlled environmental conditions to determine the toxicity of hexazinone (3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione) to red pine (Pinusresinosa Ait.) and jack pine (P. banksiana Lamb.) during their period of rapid shoot elongation in spring and after initiation of overwintering buds in August. Red pine was a minimum of 10- and 12-fold more tolerant to soil-applied hexazinone than was jack pine on the basis of effective concentration values (EC50, the herbicide concentration that results in a 50% growth reduction compared with the control) for root dry weight and shoot fresh weight, respectively. In the spring experiment, EC50 values were approximately 0.062 and 1.75 kg a.i. (active ingredient)•ha−1 for jack pine and red pine shoot fresh weights, respectively. For root dry weight, EC50 values were roughly 0.04 and 2.0 kg a.i.•ha−1 for jack pine and red pine, respectively. Except for a somewhat reduced sensitivity in jack pine, similar results were obtained with soil applications of hexazinone after bud initiation in August.