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USDA Study Finds Weeds Flourish with Climate Change

(Beyond Pesticides, July 18, 2008) A recent New York Times report on current U.S. Department of Agriculture research shows weeds flourishing from increasing levels of carbon dioxide in the atmosphere. Lewis Ziska, PhD, and his team of researchers, have found “noxious” weeds to be more adaptable to changing conditions than crops, predicting further growth of their productivity and range in urban and rural areas.

Dr. Ziska’s latest research focuses on weeds uniformly grown at three sites in Maryland: an organic farm in the western side of the state, a park in a Baltimore suburb, and a reclaimed industrial area in Baltimore’s inner harbor. The last was chosen because the city acts as a “heat island,” with temperatures averaging three or four degrees above those outside the city. Dr. Ziska’s team took soil from the organic farm, which already contained seeds from 35 weed species, and transplanted them into identical plots at the three locations, beginning the experiment in 2002.

The resulting plants tended to grow much larger closer to the city. Lambs-quarters grew six to eight feet on the farm and ten to 12 feet in Baltimore. Ailanthus grew five feet tall on the farm, compared to one in the city reaching 20 feet. Pollen output was also increased. Species succession, a process which takes native species decades to complete, was almost achieved by the end of five years of growth.

Of the changing climate and increasing carbon dioxide levels, Dr. Ziska said, “When you change a resource in the environment, you are going to, in effect, fabor the weed over the crop. There is always going to be a weed poised genetically to benefit from almost any change.”

According to the Times, weeds cost U.S. farmers 12 percent of their harvest, or $33 billion per year in lost revenue. Increased threat of weeds are leading companies like Monsanto to develop “Climate Ready” crop seeds, which are genetically altered to withstand drought and higher temperatures, and which promise huge financial incentives to their patent holders. Genetically engineered crops have a complicated and controversial history, globally and nationally, and have been found to increase pesticide use and resistance. According to Dr. Ziska, the answer is not to constantly change the tools with which we fight weeds, but to look to weeds and wild relatives of crops for the answer.

Sources: New York Times, Treehugger


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