Effects of moisture stress on absorption, translocation, & distribution of 2,4-dichlorophenoxyacetic acid in bean plants

Abstract

Applications of herbicides such as 2,4-dichloro-phenoxyacetic acid (2,4-D) and 2,4,5-trichlorophen-oxyacetic acid made locally during the summer months for the control of oak brush are often not as effective as those made during the spring or fall (H. M. El-well, 1961, personal communication), indicating that moisture stress within the plant may be important in determining the effectiveness of these compounds as herbicides. There have been few attempts to measure directly the significance of the actual water deficit within the plant in regard to the absorption and translocation of 2,4-D. The effects of temperature and humidity have been studied in relation to their effect on 2,4-D absorption and translocation, and these factors may have an indirect influence on the moisture stress in plant cells. Pallas (10) reported that the soil moisture level caused marked effects on the translocation of 2,4-D. Plants growing in soil with a moisture level near the permanent wilting point translocated only half as much 2,4-D as plants growing in soil at field capacity. Soil moisture did not affect the absorption of the herbicide when it was applied on one unifoliate leaf. Hauser (4) reported, however, that less 2,4-D was absorbed by plants grown under moisture stress. Some of the factors which may have an indirect effect on water stress of plants have been reported to affect 2,4-D absorption and translocation. The absorption of 2,4-D was reported to be made greater by increasing the temperature [Rice (12), Hauser (4), and Barrier & Loomis (1)]. Translocation was reported to be made greater by increasing the temperature [Pallas (11)] and the data of Barrier & Loomis (1) and Hauser (4) suggested that high temperatures favor translocation. Our present work has been directed toward determining the effects of the actual moisture stress within the plant (as measured by relative turgidity) on the absorption, translocation, and distribution of 2,4-D in bean plants. We also investigated the time necessary for bean plants to regain the ability to translocate 2,4-D after being exposed to drought conditions. I Manuscript received March 2, 1961.