Comparison of chemical and manual methods of precommerical thinning oak stump-sprouts

Precommercial thinning of 12-year-old upland oak stump-sprouts in southwestern Virginia using herbicides and manual felling was compared. Objectives were to quantify and compare residual crop-stem growth and treatment costs between treatments and application methods. 2,4-D and triclopyr were applied to competing stump-sprouts using stem injection and low volume basal spray techniques. Kerosene, the carrier for the ester formulations, was also tested for its efficacy properties. One growing season following treatment, total control (percent affected and dead) of chemically treated sprouts averaged 98 percent. Triclopyr basal spray treatment exhibited the highest mortality to treated sprouts totaling 88.6 percent and kerosene had the lowest mortality occurrence of 7.6 percent. On average, translocation was minimal affecting only 58 percent of the crop-stems with less than 10 percent of the crown exhibiting visual symptoms. Mortality of residual crop-stems did not occur and an average of 36 percent exhibited no visual symptoms. Mean height growth for residual crop-stems was significantly greater for manual thinning over unthinned control. Crop-stem height growth was also significantly greater for the contrasts of manual thinning vs chemical thinning and manual thinning vs basal spray treatments. No significant differences occurred for any growth parameter between unthinned control and chemical treatments nor between injection and basal spray treatments. Results of regression-adjusted volume growth (D²H) showed that a 2 percent increase in growth over control was realized for the crop-stems following injection treatments versus a 1 percent increase as a result of the basal treatments. The manual thinning treatment was found to exhibit a significantly greater effect on crop-stem growth compared to chemical treatments averaging a 4 percent volume growth increase. Chemical treatment costs ranged from $36.05/ha to $82.23/ha for 2,4-D injection and triclopyr basal spray treatments, respectively. Manual thinning was found to be the most expensive treatment at $105.30/ha. Injection treatments were significantly more productive and the least expensive. Application costs incurred during the present study were representative of costs incurred by forest industry, private, and public agencies in the southern United States. Overall results of this study suggest that chemical pre-commercial thinning of oak stump-sprouts is a safe, cost effective method of reducing competitionand releasing dominant crop-stems.