9 Weed Management

9.1 Weed Management Research in Asparagus, compiled by Dr. Bryan Brown

In establishing asparagus, it is important to plant in an area with minimal weed pressure, especially from aggressively spreading perennial weeds. Preparing fields in advance of planting with repeated tillage and smother crops can help reduce weed problems that occur in the early period of establishment when asparagus is especially sensitive to competition. Once asparagus ferns create a canopy, weed competition is reduced, but emerged spears provide little shade to reduce competition. As such, weeds need to be removed during the harvest period.

Mechanical cultivation prior to spear emergence can help reduce overwintering weeds before harvest. In-season hand-hoeing is most effective with tools that can fit between ferns. One study found that rototilling up to a 3.5 inch depth before or after harvest caused minimal damage to the asparagus crowns. Tilled borders around asparagus plantings can also prevent perennial weeds outside the area from creeping into the cultivated area. Grazing animals may potentially be used when asparagus is dormant if there is a sufficient pre-harvest interval. Weeder geese have been shown to also reduce snails in asparagus. Mechanically shredding fern fronds and burning residue at the end of the growing cycle can eliminate weed seeds as well as disease inoculum.

Loose mulches such as straw, bark, sawdust, wood chips, pine needles, grass clippings, or chopped leaves in a 4-inch depth have been shown to be effective between rows. However, these materials may delay spear emergence. Plastic mulch is not used typically, unless growing white spears. Many studies have investigated living mulches to suppress weeds between rows. Grasses or grass/legumes mixtures are often used. But these living mulches have little effect on perennial weeds and can compete with the asparagus, reducing yields.

Flame-weeding can be used during the harvest period, fern production, and at the end of the growing cycle. Flame-weeding with liquefied petroleum gas at a rate of 38 to 77 lb/ac was shown to cause minimal damage to spears during harvest.

9.2 Additional Weed Management Resources

For more information and a summary of OMRI-listed products available for weed control, see the Weed Management for Organic Vegetable Production chapter.