Six, 9, and 12-mm diam dicalcium phosphate tablets were evaluated for their release of acetochlor, metolachlor, and metribuzin. Greenhouse bioassays with Italian ryegrass demonstrated that herbicides from the smaller tablets did not control grass as long as from the larger tablets. Italian ryegrass was controlled within a 5- to 7-cm diam circle around the 12-mm diam tablet and a 5-cm diam circle around the 6-mm diam tablet. All tested herbicides responded in a similar fashion. Six-mm diam tablets released metolachlor for 11 weeks, while the 12-mm tablet was active for 28 weeks.

Cucumber [Cucumis sativusL. ‘Calypso′] susceptibility to the ethyl ester of quizalofop {2-[4-[(6-chloro-2-quinoxyalinyl)oxy] phenoxy] propanoic acid} was investigated under field and greenhouse conditions. Cucumber yield was significantly reduced under field conditions with a single or repeated application of quizalofop at 0.14 or 0.28 kg ai/ha. Under greenhouse conditions, quizalofop significantly suppressed cucumber plant fresh weight with or without the presence of an adjuvant. Enhancement of herbicide activity was related to the concentration of adjuvant. At a higher rate of quizalofop, addition of the lower concentration of an adjuvant increased the herbicidal effect (growth suppression and visually estimated phytotoxicity). At a lower concentration, increasing adjuvant concentration enhanced visually estimated phytotoxicity.

A mechanism of action of the ethyl ester of quizalofop was determined in monocotyledonous and dicotyledonous plants. Quizalofop inhibited electron transport in both cucumber and corn chloroplasts. In corn, inhibition of electron transport was more pronounced under phosphorylating conditions. Half-maximal inhibition (I50) of ATP synthesis was achieved with a 75-μM concentration of quizalofop in coupled corn chloroplasts. Cucumber chloroplast ATP synthesis was not inhibited at herbicide concentrations up to 100 μM. Corn chloroplast fractions contained greater quantities of bound [U-14C] quizalofop ester following incubation in light and dark assays. Thin-layer radiochromatograms of14C-labeled quizalofop showed no metabolism or degradation of parent ester incubated in light and dark chloroplast-mediated reactions. In our studies, it is apparent that the inhibitory action of quizalofop was due to the parent ester. The ester formulation of quizalofop appears to exhibit multiple activity in susceptible plant chloroplasts.

No abstract

Alachlor (2-chloro-2',6'-diethyl-N-(methoxyinethyl) acetanilide), chloramben (3-amino-2,5-dichlorobenzoic acid), naptalam (N-1-napthylphthalamic acid (2-N-1-naphthy) aminocarbaryl benzoic acid), and propachlor (2-chlor-N-isopropylacetanilide) incorporated into dicalcium phosphate and plaster of paris slow-release tablet formulations successfully controlled weeds for 16 weeks with no significant injury to cotoneaster (Cotoneaster dammeri C.K. Schneid. ‘Royal Beauty’), euonymus [Euonymus fortunei (Tarcz.) Hand Mazz. ‘Emerald ’N Gold’], forsythia (Forsythia X intermedia Zab. ‘Spring Glory’), ind privet (Ligustrum X vicaryi, a hybrid between L. ovalifolium Hasst. ‘Aureum’ and L. vulgare L.). One tablet per container was applied, delivering 20 or 40 kg/ha active ingredient. Metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide) was incorporated in the tablet formulations to deliver a rate of 40 kg/ha active ingredient per tablet to evaluate area of weed control. Weed density was significantly reduced in containers treated with metolachlor tablets. An essentially weed-free area (7- to 8-cm radius) encompassing a single herbicide tablet was observed. Tablet formulations did not significantly differ in reduction of weed density in nursery containers.