In order to kill a tree that size, you would get the best results cutting the tree down to a stump and treating the fresh cut stump directly. If the trunk diameter is less than 6-8 inches, then you could potentially do a basal bark treatment with the Hi-Yield Range and Pasture Triclopyr + D. You would mix approximately 5 ounces per gallon of solution, mixing in diesel No. 1 or 2 or kerosene, then spraying the basal part of the tree up to a height of 15-20 inches off the ground. If you do not need this much product, then could also use Fertilome Brush Killer and Stump Killer.
Hi-Yield Range and Pasture Triclopyr + D mix rate is approx. 1.5oz per gallon water. Be sure to follow the product label.
Hi-Yield Range and Pasture Triclopyr + D is not non-selective. It will only control woody plants and annual and perennial broadleaf weeds that are growing in a pasture. This product will not harm any permanent pasture or range grasses.
Do not apply under circumstances where spray drift may occur to food, forage, or other plantings that might be damaged or crops thereof rendered unfit for sale, use or consumption. Susceptible crops include, but are not limited to cotton, okra, flowers, grapes (in growing stage), *fruit trees (foliage)*, soybeans (vegetative stage), ornamentals, sunflowers, tomatoes, beans, and other vegetables, or tobacco. Small amounts of spray drift that might not be visible may injure susceptible broadleaf plants