WESTMINSTER, Colorado – November 19, 2019 – New Jersey is the nation’s third-largest cranberry producer. But according to the Weed Science Society of America (WSSA), growers in the state are fighting a tough battle to keep the colorful berries on your holiday table. Their crops are being threatened by Carolina redroot, a native perennial weed that competes with cranberry plants for nutritional resources.
Thierry Besançon, Ph.D., a weed scientist with the Rutgers Center for Blueberry and Cranberry Research and Extension, says cranberry bogs provide a perfect environment for redroot to flourish. The weed thrives in sandy soils and in watery ditches, bogs, swamps, lakes and wetlands along the Atlantic coastline.
“We estimate Carolina redroot can now be found in 70 to 80 percent of the cranberry bogs in the state,” he says. “Nearly a third of growers are battling large-scale infestations.”
The impact on crop yields can be devastating. Studies show that Carolina redroot density can reach 500 plants per 10 square feet of bog, causing growers to lose 80% of cranberry yields.
Fighting Carolina redroot is tough since it largely spreads through specialized underground stems called rhizomes. If you try to remove the weed manually, new plants can grow from any small fragment left behind. To compound the issue, the same bright red rhizomes also serve as an important food source for waterfowl. As swans and geese dig through the bog to feed, they destroy sections of the cranberry crop and break the redroot rhizomes into small pieces that contribute to the weed’s rapid spread.
After conducting multiple studies on how to best control Carolina redroot, Besançon suggests a multipronged approach:
- Scout for new infestations. “When you catch Carolina redroot soon after it has emerged, you have a higher chance of winning,” he says. He recommends regular scouting, especially around irrigation trenches and openings in the cranberry canopy where redroot can establish. Large-scale growers who find it hard to monitor broad expanses may want to automate the process by using drones equipped with spectral imaging technology.
- Use tarps. Spot treat early infestations by covering the weed to block sunlight. Researchers have found that 45 days of complete darkness can significantly reduce the production of new biomass and can totally suppress rhizome production to keep redroot from spreading. Interestingly, none of the other cultural controls researchers have explored seem to work. Carolina redroot can be buried under many inches of sand or covered by water for months on end and still survive and spread.
- Fight fungi. When cranberry vines are attacked by a fungus causing fairy ring disease, the withering foliage can create openings in the crop canopy where Carolina redroot can grow. It is important to keep the crop healthy and to maintain a thick canopy. When necessary, use fungicides and other methods to control disease.
- Apply pre- and post-emergence herbicides. Besançon says herbicides represent the best control option. The preemergence herbicides napropamide and dichlobenil can suppress Carolina redroot for four to six weeks after application. Mesotrione applied after the weed has emerged can provide more than 90% control of both shoots and rhizomes for more than two months.
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About the Weed Science Society of America
The Weed Science Society of America, a nonprofit scientific society, was founded in 1956 to encourage and promote the development of knowledge concerning weeds and their impact on the environment. The Society promotes research, education and extension outreach activities related to weeds, provides science-based information to the public and policy makers, fosters awareness of weeds and their impact on managed and natural ecosystems, and promotes cooperation among weed science organizations across the nation and around the world. For more information, visit www.wssa.net.
Editor’s Note: Supporting photos are available for download online at https://wssa.net/2019-holiday-release.
Lee Van Wychen
Executive Director of Science Policy
National & Regional Weed Science Societies