Mark Schonbeck, Virginia Association for Biological Farming
Once the farmer has designed the cropping system to minimize opportunities for weed growth, the next step is to develop strategies for dealing with those weeds that will inevitably emerge. Because weed control is one of the largest costs in vegetable production, careful planning to get the most weed control for the least time, fuel, and other resources can be vital to the farm’ economic bottom line. These steps include:
Farmers, researchers, and agricultural engineers have developed a wide range of tools for precision cultivation, flame weeding, and other weed control tactics in many different vegetable and row crops. These are described in greater detail in An Organic Weed Control Toolbox.
Planning begins with evaluating equipment and other resources already on hand, and deciding what additional weed control implements are needed. When choosing tools and tactics, consider the following questions:
Suppose edamame soybean is a major crop on a 20-acre vegetable farm. Major weeds include lambsquarter, pigweed, and crabgrass, and the farmer knows from experience that removing these weeds from within crop rows is essential for maintaining satisfactory yields. Manual weeding is effective but impractical for several acres of soybeans. The grower will want to invest in a cultivation system that effectively removes weeds both between and within crop rows during the crop’s critical weed-free period. Soybean is a crop that can be blind cultivated just prior to emergence, a practice that delays weed development relative to the crop, and thereby allows the effective use of finger weeders, torsion weeders, or other light duty tools that can remove small within-row weeds without damaging the crop. Thus, a rotary hoe for preemergence blind cultivation may be a wise investment in this situation.
Other crops such as sweet corn, Irish potatoes, and broccoli tolerate and even benefit from hilling-up once they are established. For these crops, a simple, inexpensive between-row cultivation system with sweeps or rolling cultivators can be adjusted to throw soil into crop rows. The implement simultaneously severs between-row weeds and buries weeds within or near crop rows under an inch or two of soil—sufficient to kill small weed seedlings.
Organic mulch can be an effective tactic for certain crop–weed combinations, particularly summer annual broadleaf weeds in crops like tomato that respond favorably to mulch. Black plastic mulch may work better for heat-loving crops when an early harvest is desired, or against grass and perennial weeds that can penetrate organic mulch. If plastic mulch is used, it must be removed from the field at the end of the growing or harvest season.
Because spreading organic mulch manually becomes costly at the multiacre scale, some growers roll down cover crops to create an in situ mulch for transplanted crops. However, if many perennial weeds are observed in the fields, it is not the right time to invest in a crimp roller for turning cover crops into mulch. The first priority is to knock out the perennial weeds, which rolled cover crops cannot accomplish (for more, see Bring Existing Weeds Under Control Before Planting Weed-Sensitive Crops).
A flame weeder can be a good investment for crops, like corn, that can tolerate the brief blast of heat at certain stages of development. In addition, flame weeding just before emergence of small-seeded, slow-germinating crops like carrots, parsley, and beets can wipe out any emerged weeds, and thereby give the crop a vital head start on weed competition.
Prevailing soil conditions can also influence the choice of tools. Efforts to improve soil tilth through good organic management often pay off by making cultivation easier and more effective. In fields where soils tend to remain somewhat wet regardless of management, standard sweep cultivators may tend to become clogged, and other implements better suited to moist soils may be needed. In stony soils, sturdy implements and implements equipped with spring mechanisms—such as a springtooth harrow—are less likely to become damaged by impacts with stones than light duty rigid tine harrows.
In developing a weed control system, take care to match crop row spacings and bed dimensions with tractor wheel width and the dimensions and configurations of cultivation implements, flame weeders, and mulch layers. Diversified vegetable production can make the decisions complicated, since the various crops may require row spacings from as narrow as 4–6 inches to as wide as 4–6 feet. However, using row spacings that are multiples of one another and are compatible with equipment dimensions can simplify logistics and make weed management far more labor efficient (see example in sidebar).
Farm consultant Josh Volk (2008) recommends the following 3–2–1 row system for cultivating diverse vegetable crops:
Small crops can be grown three lines to a bed; for slightly larger plants leave out the middle row and you have two rows, or for the largest plants only plant the center row and you have one row; thus 3–2–1. Most tractor cultivating happens when the plants are small, regardless of how big they will get. The same cultivating setup can be used in all three situations without ever changing [it]…
A basic setup for a 3–2–1 bed would be to have two sweeps running behind the tire tracks to clean up the pathways on the outsides of the plants. Two more sweeps would be mounted between the rows to clean up the bed top. If you want to get a little fancier, add a second tool bar, slightly behind the first, with three more sweeps, one directly in line with each row. If you’re cultivating a two-row crop you would drop the middle sweep and mount the two outside sweeps upside down (with the shanks facing up) so that they’re effectively out of the row. If you’re cultivating a single line crop, you would drop the two outside sweeps and lift the middle sweep.
~ Volk, 2008
Farm-scale organic production of weed-sensitive crops like carrots and onions may require sophisticated weed-management strategies that can entail significant investment. In addition to the right combination and configuration of implements tailored to the specific crop, successful weed control often depends on a guidance system to ensure high precision planting and cultivation to avoid damaging the crop. Often, crop row configurations need to be adjusted to match cultivation equipment.
For example, researchers working with organic carrot farmers in Italy developed an integrated weed control strategy that yielded substantial net savings in labor costs (Peruzzi et al., 2007). The growers’ standard production system was to seed carrots in five 3-inch-wide bands spaced 12 inches apart (center to center) on a 6-foot wide bed, flame-weed preemergence, tractor-cultivate between crop bands, and hand-weed within bands. The experimental strategy changed the planting pattern to ten rows spaced 7 inches apart, and utilized an innovative precision cultivating machine that combined 3.5-inch between-row sweeps with vibrating tines and torsion weeders for weeds near and within crop rows. This system reduced total weed control labor costs and often enhanced carrot yield.
What if the ideal weed control tools for a particular crop or situation are not available, or are not affordable within the farm’s budget? Many farmers innovate, developing their own unique strategies and fabricating tools for a fraction of the cost of purchasing equipment. For example, David Stern of Rose Valley Farm in Rose, New York developed new ways to use old tools and human skill:
David has designed two implements that combine the efficiency of tractors with the fine precision of the human eye and hand, which he describes as ‘the most accurate weeding tool we have.’ The platform weeder/harvester is a homemade platform on a three-point hitch that adjusts so a person can lie comfortably on a foam mat and hand-weed crops (small to large) as the tractor moves slowly through the field. The wiggle hoe is a three-point tractor-mounted tool modified from the horse-drawn cultivators of our grandfathers. A person sits comfortably, directly over a row of vegetables, and with handheld, mounted tools, can very accurately and closely cultivate at a shallow depth.
~ Schonbeck, 2007
The wiggle hoe resembles a light duty version of the Regi weeder, a PTO-driven device consisting of two rotary disks with hayrake teeth guided manually from behind to effect within-row weeding.
This article is part of a series on Twelve Steps Toward Ecological Weed Management in Organic Vegetables. See also An Organic Weed Control Toolbox, and the following video clips:
This is an eOrganic article and was reviewed for compliance with National Organic Program regulations by members of the eOrganic community. Always check with your organic certification agency before adopting new practices or using new materials. For more information, refer to eOrganic's articles on organic certification.