Review of Mechanical Weed Control Options in Vegetable Crops

Weed control between and especially within the rows is critical in vegetable crop production. Although herbicides represent an efficient means of controlling weeds both within and between the rows, herbicide options are limited for many vegetable crops. Plastic mulches are useful for controlling weeds within the row but do little to slow weed growth between the rows. Hand weeding represents a last resort due to the cost.

At one time, mechanical tillage was the primary means of weed control in almost all crops. As costs of alternate methods of weed control increase, many growers are re-evaluating mechanical weed control options in their vegetable crops. Kelly, Pritts and Bellinder of Cornell University New York have recently published an interesting review of the performance of mechanical weed control options (HortTechnology 2007, vol 17 p 87-94). They consider use of the single or multi-unit rotary cultivators to be the present standard approach to mechanical weed control. Although these units can be very effective for weed control between rows, they are of limited value for control of weeds within the row. Additional downsides are the fact that rotary cultivators are; a) slow, b) tend to move weed seeds within the soil profile resulting in multiple weed flushes, c) cause compaction and general degradation of soil structure and d) do not work well in heavy textured wet soils.

Kelly and associates point out that the alternatives to rotary cultivators all have weaknesses as well as strengths. Flex tine harrows are fast, low cost and when properly adjusted and operated can do a decent job of controlling weeds both within and between rows. However, the efficacy of weed control achieved with flex-tine harrows can be highly variable, depending on the number of passes made, the size, type and number of weeds present in the field and the soil and weather conditions at the time of cultivation. Spider-type and finger hoes are also fast and relatively affordable ground driven units. Spider hoes do a decent job of controlling weeds between rows but are of limited value within the row, while finger weeders are gentle enough to provide weed control within the rows but are not aggressive enough to provide thorough weed control between the rows.

Brush weeders are a relatively recent development – these units work and look like street sweepers, with the rotating brushes shredding bigger weeds and smothering smaller weeds. If properly adjusted, brush weeders can be used both between and within rows without causing excess crop damage, at least in more robust crops like broccoli, corn and beans. As the brush weeder provides only minimal soil disturbance they do not promote multiple flushes of weeds. However, on the downside, brush weeders are slow, heavy and costly PTO driven units that can be difficult to adjust to differing row spacings.

Source: Kelly, Pritts and Bellinder (2007) HortTechnology 17: 87-94