Alternative Tillage and Herbicide Options for Successful Weed Control in Vegetables

Abstract

Increased federal and state regulations resulting from concerns for pesticide-free food and protection of ground water have created the need to reevaluate weed control strategies that currently depend on chemicals (Sweet et al., 1990). Cultivation and hand-weeding are feasible for small-scale growers but are usually not economical for large, commercial growers. Weed control in vegetables relies heavily on soil-applied, preemergence herbicides. However, with the development of selective, postemergence herbicides that can be applied as needed, growers may now fine-tune weed control strategies, combining the new herbicides with reduced rates of soil-applied herbicides and cultivation. Reducing inputs and integrating farming practices to lower costs and reduce environmental impacts while maintaining successful weed control is difficult (Edwards and Regnier, 1989). However, strategies that may reduce chemical inputs include: delaying applications of reduced rates of preemergence herbicides, banding herbicides over the crop row, using mulch and reduced tillage systems that aid in weed suppression, tank-mixing low rates of post-and preemergence her-bicides, applying postemergence herbicides after cultivation, and using new, environmentally "soft" herbicides that are active at extremely low doses. The objective of this paper is to discuss previous and current research that integrates tillage, mulches, and low-rate applications of herbicides for use in commercial vegetable production. Herbicide rate reduction The use of low-rate herbicide applications is not new. Akobundu et al. (1975) evaluated low-rates of atrazine and alachlor for postemergence use in sweet corn (Zea mays L. var. saccharata) to reduce carryover and facilitate crop rotation. Recently, successful reduced-herbicide weed control programs have been reported for several crops. When postemergence herbicides were applied twice at one-half to one-fourth (0.5× to 0.25×) the standard rate (1×) in soy-HORTSCIENCE, VOL. 27(7), JULY 1992 beans [Glycine max (L.) Merr.], broadleaf and grass weeds were controlled (Defelice et al., 1989). However, when reduced herbicide rates were applied once, weed control was not adequate. Nonselective, postemergence herbicides used in double-cropped, no-till soybeans, may be reduced or eliminated from weed control programs when herbicides having both pre-and postemergence activity are applied (Moseley and Hagood, 1991). Control of redroot pigweed (Amaranthus retroflexus L.) and common lambsquarters (Chenopodium album L.) in potatoes (Solanum tuber-osum L.) was equivalent with both 1× and 0.67× rates of oryzalin, metribuzin, and linuron (Wallace and Bellinder, 1990). Similarly, low rates of trifluralin (tomatoes [Lycopersicon esculentum Mill.]) or trifluralin plus oxyfluorfen (cauliflower [Brassica oleracea L. var. botrytis]) provided adequate weed control compared with standard rates (Maynard and Bellinder, 1989). Cardina et al. (1987) combined reduced rates (0.67× to 0.33×) of benefin and vernolate with multiple postemergence applications of paraquat in peanuts (Arachis hypogaea L.) and found that weed control was equivalent to that of the chemical standard but cost 40% less. Lanini and Le Strange (1991) reduced preemergence herbicide rates, and when this was coupled with a single hand-weeding, vegetable yields were equivalent to or better than those of the full-rate chemical program or season-long hand-weeding. While reducing rates may lower the total amount of chemicals applied, control of some weeds may not be satisfactory. Wallace and Bellinder (1990) reported that a reduced rate of metolachlor failed to control redroot pigweed. Tank-mixing two or more herbicides at reduced rates may increase the spectrum of weeds controlled and decrease the risk of inadequate weed control. Mixing post-and preemergence herbicides increases flexibility in weed management strategies. Shilling et al. (1986) applied diphenamid and glyphosate to cereal grains used for mulches in no-till tobacco (Nicotiana tabacum L.). Glyphosate killed the mulches while 745