Carbohydrate Levels and Control of Blackjack Oak and Winged Elm Treated with Tebuthiuron and 2,4,5-T

Abstract

The effects of tebuthiuron N-[S(l,l-dimethylethyl)-1,3,4-triadiazol-2-yl]-N,N’ dimethylurea) and 2,4,5-T[(2,4,$trichlorophenoxy) acetic acid] on total nonstructural carbohydrates (TNC) in the roots of blackjack oak (Quercus marilundicu Muench.) and winged elm (Ulmus alutu Michx) were evaluated. Tebuthiuron was applied to the soil in February 1976 at 2.24 kg/ha and 2,4,5-T was foliar applied at 2.24 kg/ha in May 1976. Tree kill 1 year after treatment with tebuthiuron was 100% for both woody species. No tree kill resulted from treatment with 2,4,5-T, and canopy reduction after 1 year was 50 and 70% for winged elm and blackjack oak, respectively. The TNC content of both winged elm and blackjack oak roots was significantly reduced followihg application of 2,4,5-T and tebuthiuron. The TNC content of roots from trees growing in tebuthiuron-treated areas did not significantly increase after treatment (TNC contents of 6 and 7%, respectively for blackjack oak and winged elm on October 13). There was some increase in TNC content of roots from trees sprayed with 2,4,5-T, and by October the TNC content in blackjack oak and winged elm roots was 10 and 19%, respectively. This compared to TNC contents of 36 and 32%, respectively for untreated blackjack oak and winged elm. Phenoxy herbicides, such as 2,4,5-T, have been the herbicides most commonly used for brush control. Elwell (1964) and Darrow and McCully ( 1955) indicated that two aerial applications of 2,4,5-T totaling 3.36 to 4.48 kg/ha, with not more than 2 years between treatments, were required to effectively control blackjack oak (Quercus marifundica Muench.) and post oak (Quercus stellatu Wangenh.). Elwell(l968) concluded that foliar applications of 2,4,5-T did not effectively control winged elm (Ulmus afuta Michx.). Stritzke (1975) found that the addition of ammonium thiocyanate to 2,4,5-T consistently increased control of winged elm compared to 2,4,5-T alone. Canopy reduction after treatments with 2,4,5-T was often short-lived since resprouting soon occurred. This resprouting has been attributed to carbohydrate reserves in the roots of the treated trees. Tebuthiuron has shown promise for control of certain brush species. Soil treatments of 2.24 kg/ha on mixed brush have given excellent control of elms (Ulmus spp.) and oaks (Quercus spp.), (Stritzke 1976, Nickels and Stritzke 1977). Baur and Bovey ( 1975) observed good control of yaupon (Ilex vomitoria Ait.), post oak, and blackjack oak with soil applications of tebuthiuron using 2.24 to 4.48 kg/ha. There is usually only the initial defoliation of trees treated with 2,4,5-T; whereas, there