Interrow Management

Blueberries do not have extensive root systems. As a result, clean cultivation of row middles to control weeds and to incorporate cover crops is less damaging to blueberries than it is to bramble fruits. Still, it is wise to till no deeper than 3 inches. Similarly, inter-row living mulches—also called sodded middles — generally are not competitive with the crop unless the inter-row species are aggressive and invade the rows. Fescue is commonly used in the Mid-South for sodded middles, as are several other grass species.

Timely mowing—usually three to five times per year—is the common means of controlling weeds and other vegetation in sodded middles. It is most important that weeds not be allowed to produce seed that may be scattered into the rows and germinate later.

In a Texas study, researchers demonstrated that the inter-row area could be used to produce significant quantities of mulch for rabbiteye blueberries. Successful winter crops of rye, rye-grass, and crimson clover, and a summer crop of pearl millet, were grown, cut, and windrowed onto the blueberry rows. Nitrogen proved the major limiting factor for non-leguminous cover crops; low soil pH and browsing deer limited the biomass production of legumes. Pearl millet demonstrated the greatest level of allelopathic (natural production of plant chemicals by one plant that inhibit other plants growing nearby) weed suppression.(Patten et al., 1990)

In some systems that employ sodded middles, a weed-free strip 6 to 12 inches wide often is maintained between the edge of the mulch and the cover crop. The strip reduces competition between the cover crop and berry bushes, and lessens the chance that weeds or the cover crop itself will advance into the mulch. It has the added advantage of discouraging cutworms, an occasional pest in blueberries. In organic systems, this strip is maintained without the use of herbicides.

Organic growers typically employ mechanical cultivators of various types to maintain the weed-free strip. Gordon Watkins (1989) described two modified "off-the-shelf" cultivators used by growers in the Ozark region. One, referred to as the Vasluski Edger, uses a single disc from a rice levee plow in conjunction with two shanks from a spring-tooth chisel. These are mounted on a tool-bar that extends past the rear tractor tire. The disc cuts a strip along the row edge and throws soil towards the plants, while the shanks stir soil closer to the bed. The result is a weed-free strip about 6 to 8 inches wide. The drawback of this implement is the amount of dirt shifted by the disc and the resulting "ditch."

The second implement Watkins describes is the Lilliston Rolling Cultivator,™ with all the heads removed except the two extending beyond one rear tire. One head rolls in the ditch area that is (or would be) created by the Vasluski Edger. The second extends approximately 12 inches onto the side of the bed. Depth of penetration is set at 1 inch, and the implement is best operated at relatively high speeds. Since it cultivates about one-half of the bed surfaces, only about a 2-foot strip remains for hand pulling and hoeing. The tool works well on small weeds but does not control larger, well-established weeds.

Flame, steam, and infrared thermal weed-control systems are other options. In the 1980s and '90s, flame weeding made a rapid comeback as a non-chemical weed control technique, especially among organic farmers. However, this technique is not always practical or safe around flammable mulch materials. ATTRA can provide additional information on flame weeding.

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