Summary. Studies were conducted to determine the effects of herbicide placement at different zones of maize (Zea mays L.) and pea (Pisum sativwm L.) shoots below the soil surface after emergence. Soil was removed from around the shoots and replaced with herbicide‐treated soil. A wax barrier ensured separate exposure of the zones to treated soil. EPTC, chlorpropham, propham and sulfallate did not affect pea shoot growth, but in maize the shoot zone adjacent to the crown root node was extremely sensitive. Treatment in this area markedly reduced growth and severely inhibited the crown roots. The difference in susceptibility between these species may he due to the location of the growing point relative to the treated soil. Shoots of maize and pea were sensitive to diuron. In maize the shoot adjacent to the crown root node and the tissue of the first internode were the most susceptible. In pea the‐ uppermost shoot (beneath the soil surface) was the most sensitive. Trifluralin did not affect growth of maize and pea when placed in the shoot zone after emergence, although the crown roots of maize were severely inhibited. Naptalam, dalapon and 2,4‐D did not affect growth of maize under similar conditions, and of these only 2,4‐D reduced growth of pea. Zone d'abiorption des tiges pour les herbicides appliqués sur h sol

Summary. We conducted studies to determine the effects on corn (Zea mays L, var. Indiana 654) and pea (Pisum sativum L. var. Alaska) of localizing various herbicides in the soil, using a double plastic pot technique which ensured separate exposure of the root and shoot zones of the plants to treated soil. Effects on corn and pea were similar in relation to site of uptake. 2,4‐D‐amine, naptalam, simazine, diuron and dalapon‐sodium entered primarily through the roots. Some shoot entry and also severe inhibition of roots occurred in soil treated with 2,4‐D and naptalam; these were noticed only to a slight extent with the other three herbicides. EPTC, chlorpropham and trifluraiin were most effective when applied to the shoot zone. Little effect on foliage growth was evident when the root zone alone was treated. However, roots in treated soil were severely inhibited by these three herbicides. Dinoseb displayed a contact type of action, injuring both shoots and roots. Treatment of both zones had an additive effect. Entry of chlorthal‐methyl which was tested on a susceptible species, sorghum (Sorghum vulgare Pers.) was mainly through the shoot, with only a slight effect on top growth when roots alone were treated. Roots in treated soil were slightly inhibited. Localisation de l'absorption des herbicides appliqués sur le sol

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Summary: Leakage of electrolytes from leaf discs of treated Phaseolus Vulgaris L. plants was the main criterion used to study the effect of several chemicals on the permeability of leaf‐cell membranes. Paraquat, diquat, dinoseb and oxyfluorfen (2‐chloro‐1‐(3‐ethoxy‐4‐nitrophenoxy)‐4‐(Trifluoromethyl) benzene) increased leaf‐cell membrane permeability after exposure for 12 h or less. An‘aromatic’oil caused a large increase in permeability at 2–5 min after treatment. Increases in electrolyte release were also correlated with release of soluble amino acids from the leaf discs but the former method was the more sensitive. Increase in cell membrane permeability was always associated with injury symptoms such as appearance of necrotic areas in leaves. Chlorpropham, linuron, sodium azide, glyphosate and 2,4‐D at 10−3M, as well as 1% X‐77 surfactant and a non‐phytotoxic isoparaffinic oil did not alter leaf‐cell permeability at 12 h after treatment. Light was necessary for paraquat and oxyfluorfen to alter leaf cell permeability. Paraquat and oxyfluorfen caused a greater increase in leaf‐cell permeability of a soybean mutant with yellow leaves as compared with the normal green leaves. With oxyfluorfen this difference in permeability was greater than with paraquat, and was associated with the appearance of severe necrotic injury symptoms in the yellow mutant; paraquat caused no injury symptoms.

Antagonistic responses were noted on sorghum (Sorghum vulgarepers.) and giant foxtail (Setaria faberiiHerrm.) using preemergence combinations of (2,4-dichlorophenoxy)acetic acid (2,4-D) and the carbamatesS-ethyl dipropylthiocarbamate (EPTC), isopropylm-chlorocarbanilate (chlorpropham), and 2-chloroallyl diethyldithiocarbamate (CDEC). Combinations of EPTC and (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) or 3,6-dichloro-o-anisic acid (dicamba) gave similar results. Effects of these combinations were mainly additive on four dicotyledonous species. Combinations of 2,4-D andN-1-naphthylphthalamic acid (naptalam) also were antagonistic on sorghum and giant foxtail but were additive on the remaining species. Eight other herbicide combinations were mainly additive on all six species.