Weed management can be a significant problem for organic blueberry production. The key practices are sanitation and prevention. These practices prevent weed seed from entering the soil profile and becoming problematic. Sanitation practices include cleaning weed seed off equipment between fields, maintaining field edges, and using weedfree plant material. If weeds begin to emerge in the field; use the methods below to prevent the weeds from producing seeds and create a growing problem.
Row Middle Control
In the row middles, mowing the weeds is a very common practice. Allowing grass to grow will compete with the weeds, and raising the mowing deck to 3-4 inches tall will allow the grass to be more competitive.
If the row middles are free of vegetation then cultivation can be used and limited to the top 1-1 ½ inch to limit weed emergence from deeper in the soil profile.
University of Florida IFAS has conducted research on the use of cover crops in the row middle to smother the weeds in the row middle. They have investigated legume species such as sunn hemp, cowpeas, and clovers; grass species such as millet and sorghum Sudangrass; and mixtures of legumes and grass species. The time of year has a large impact on the species that were selected. Researchers have not been successful in obtaining grant funding for cover crop use in blueberry.
Under the Bushes
Mechanical weed management such as weed eaters, mowing, or shallow hand hoeing are the most common methods. Labor availability and cost can be prohibitive if weed populations are very high.
Some organic herbicides are approved for application in blueberry. Consult with your organic certification agency before purchasing or application. These herbicides are broad spectrum herbicides that are applied to the base of the bushes. Application should occur early weed growth before the leaves can form a thick cuticle layer. These herbicides can be expensive. Smart sprayers have an excellent application in blueberry production. The sprayers can detect the weed growth, turn on, and spray the weed. This will cut some of the cost of organic herbicides.
Landscape fabric can be used under the bushes. The fabric will control the broadleaf and grass weeds, but nutsedge may pierce through the fabric. The fabric will need to be removed and replaced after 3 to 4 years.
Some growers have asked about the use of steam. Researchers in the Pacific Northwest have had mixed results with steam as a weed management tool. The steam will control the small emerged weeds, but the quantity of water, labor to operate the slow equipment, and equipment maintenance made this method cost prohibitive compared to other practices.
None of these options are outstanding on their own. Sanitation and prevention are important to keep weeds from becoming a problem. If weed escapes to occur a combination of methods are key for organic weed management.
CREDIT:
PETER J. DITTMAR
