Defoliation of Oak, Maple, and Other Woody Plants with 2- Chloroethylphosphonic Acid and Potassium Iodide

This investigation determined the defoliation response of red maple (Acer rubrum L.), pin oak (Quercus palustris Muenchh.), and several other actively growing deciduous woody plants to 2-chloroethylphosphonic acid (68-240) and potassium iodide (KI). Applications of 68-240 alone were made at 2,500, 5, 000 and 10,000 mg per liter and each concentration in combination with 2.0% KI to 6-year-old red maple and pin oak. Treatments were made in July and included one, two, or three sprays at 1-week intervals. The best defoliation occurred with three sprays of 68-240 alone at 10,000 mg per liter. When 2.0% KI was added to 68-240, complete desiccation occurred before abscission could take place. When KI was applied alone on 1 August at 0.5, 1.0, and 2.0%, all concentrations caused 100% desiccation on red maple. With pin oak, 1.0% KI was needed to obtain 100% desiccation. Ten woody plant species from 5 to 10 feet tall were sprayed in early July with 5,000 mg per liter of 68-240. During a period of 3 weeks, black locust, tree of heaven, sycamore, and sweet gum were almost completely defoliated (80 to 100%); six other species were defoliated to a lesser extent in descending order from 60 to 20%.