Response of Southern Wax Myrtle (Myrica cerifera) to Herbicides in Florida

Abstract

Triclopyr (0.28, 0.56, and 1.12 kg ai ha−1); triclopyr + 2,4-D (0.56 + 1.12 kg ha−1); and dicamba (1.12 kg ha−1) were evaluated over 2 yr at two locations in Florida for southern wax myrtle control following spring (Mar. to Apr.) or summer (Aug. to Sept.) applications. All treatments were applied twice, 1 yr apart, except 1.12 kg ha−1 triclopyr, which was applied once in the initial year. In the first year, defoliation with triclopyr was quadratic with > 90% at 0.56 kg ha−1. In the second year, a single application of 1.12 kg ha−1 triclopyr resulted in similar (P > 0.05) defoliation compared with two applications of 0.56 kg ha−1 triclopyr. After 1 yr, increasing triclopyr rate resulted in a linear increase in mortality. After 2 yr, two applications of triclopyr at 0.56 kg ha−1 and triclopyr + 2,4-D caused lower (P < .01) mortality (45%) than a single application of 1.12 kg ha−1 triclopyr (63%). Addition of 2,4-D to triclopyr did not increase mortality. After 2 yr, two applications of 0.28 kg ha−1 triclopyr resulted in 21% mortality while two applications of dicamba were ineffective. Defoliation was often greater with spring, compared with summer applications, but often depended on treatment and location. Mortality was greater (P < 0.01) at 1 and 2 yr after summer application compared with spring application at one location, but not the other. Roots of wax myrtle were sampled on 28-d intervals in the first year and analyzed for total non-structural carbohydrate (TNC). Starch composed 630 g kg−1 of TNC in myrtle roots, with highest concentration of TNC (120 g kg−1) in March and lowest (30 g kg−1) in August.