Weed Control in Nursery Stock by Controlled Release of Alachlor

Abstract

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)-acetanilide] mixed with plaster-of-paris in concentrations of 0.5, 1, 2, and 4% (w/w) was cast into tablets of three sizes. The controlled release of the herbicide was tested by the following methods: (a) in the laboratory with eduction by soaking tablets in water, (b) in the greenhouse with azalea (Rhododendron obtuseumPlanch. ‘Richardii’) stock in container, and (c) in the lathe house with azalea stock in containers. In the laboratory experiment, the quantity of herbicide educed from tablets of equivalent volumes, weights, and concentrations were similar regardless of surface area of the three tablet sizes. Successively decreasing quantitites of alachlor were educed with each of the first 10 soakings. Following these soakings, the quantity of alachlor educed per soaking stabilized for the next 30 soakings. In both greenhouse and lathe house experiments, azalea plants treated with as much as 45 kg/ha alachlor formulated in tablet(s) were not damaged. In the best greenhouse treatments, two small tablets per container, effective weed control was obtained for up to 7.5 months from a single application of alachlor at rates of 11, 22, and 45 kg/ha.

Innovative Herbicide Application Methods and Their Potential for Use in the Nursery and Landscape Industries

“…Public-and private-sector scientists have been researching novel methods of herbicide application that may have applications to the nursery and landscape industries. These new meth-of paris or dicalcium phosphate, plus a preemergence herbicide (Koncal et al, 1981a(Koncal et al, , 1981bRuizzo et al, 1983;Smith and Verma, 1977;Smith and Treater, 1987;Smith, 1978, 1981). As these tablets are wetted by irrigation, small amounts of the herbicide are gradually released over an extended period of time.…”

“…As these tablets are wetted by irrigation, small amounts of the herbicide are gradually released over an extended period of time. The rate of herbicide release can be increased by increasing the herbicide concentration, or by changing the size or porosity of the tablet (Smith and Verma, 1977;Smith, 1978, 1981). When alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] was applied at 10, 20, 40, and 80 lb/acre (11.2, 22.4, 44.8, and 89.6 kg•ha -1 ) in tablet form, weed control generally increased with increasing rate at 51, 83, and 118 days after treatment (Verma and Smith, 1978).…”

“…Weed control with the slow-release tablets decreased to ≈60% at 5 months and gradually decreased to 10% control by 14 months after application. Smith and Verma (1977) evaluated various sizes of tablets containing 0.5%, 1%, 2%, or 4% alachlor by weight. A single application of two small, 4% alachlor in plaster of paris tablets per container of 27 square inches (177 cm 2 ) surface area, at 40 lb/acre (45 kg•ha -1 ) active ingredient, controlled large crabgrass [Digitaria sanguinalis (L.) Scop.]…”

Slow-Release Delivery System for Herbicides in Container-Grown Stock

“…Other experimental slow-release formulations have controlled the release of a herbicide from the carrier (3,4,6,9,10,12,13,14). The application of slow-release herbicides is often more complex than conventional techniques, and efficacy of weed control may not be as predictable.…”

Effect of a Nalco-Trol® II on bioavailability of glyphosate in laboratory trials

“…Polymers and related materials, used in pesticide formulations have sometimes enhanced residual activity (Dahl and Lowell 1984;Ivy 1972;Smith and Verna 1977;White and and Schreiber 1984;Gorski et al 1985;Doub and Wilson 1987;Doub et al 1987;Cadogan 1986), but at other times have shown little difference (Schreiber et al 1978). In a recent study (Doub et al 1988) polymer-encapsulated alachlor inhibited shoot growth of certain grass species much less than the emulsifiable-concentrate formulation.…”