Importance of Root, Shoot, and Seed Exposure on the Herbicidal Activity of EPTC

Abstract

A charcoal barrier method was devised to prevent the movement of S-ethyl dipropylthiocarbamate (EPTC) in the soil in order to expose certain parts of the plant without exposing the rest of the plant. Exposing the roots of barley (Hordeum vulgare L., var. Blue Mariot), oats (Avena sativa L., var. California Red), barnyardgrass (Echinochloa crusgalli L. Beauv.), annual ryegrass (Lolium multiflorum Lam.), wheat (Triticum vulgare L.), rice (Oryza sativa L., var. Belle Patna), cotton (Gossypium peruvianum Cav.), and yellow nutgrass (Cyperus esculentus L.) caused more injury than shoot exposure, while shoot exposure caused slightly more injury than root exposure to Johnsongrass (Sorghum halepense Pers.), sorghum (Sorghum vulgare Pers., hybrid Amak R-10), and peas (Pisum sativum L.). Seed exposure caused severe injury in some plant species but not others. The results obtained by this method disagree with published reports which claimed that only shoot exposure to EPTC led to injury. In numerous experiments with barley seeds accurately planted in a vertical position in a ½-inch layer of charcoal between two 1-inch layers of soil, root exposure always injured the plants more than shoot exposure. Exposing all parts (seeds, roots, and shoots) to EPTC caused the most injury to barley followed by exposing only the seeds, a combination of roots and shoots, roots, and shoots in decreasing order of injury symptoms. Similar results were obtained with oats when the depth of the treated soil above or below the seed was 1 inch, but increasing this depth to 1.5 inches or more resulted in more injury by shoot exposure than root exposure. The importance of root exposure was confirmed using another method of testing in which only the roots were exposed to the herbicide in nutrient solutions. Concentrations as low as 1 ppm of EPTC applied to the roots in nutrient solutions inhibited shoot growth of oats, barley, sorghum, and corn, while the growth of the roots was enhanced in some cases.