When it comes to controlling hay fever-triggering ragweed plants on Detroit vacant lots, occasional mowing is worse than no mowing at all, and promoting reforestation might be the best solution.
Those are the findings of a new University of Michigan study that surveyed vacant lots in several Detroit neighborhoods for ragweed, counting the number of ragweed plants and estimating how often each lot was mowed.
The researchers found that ragweed was significantly more likely to be present in vacant lots mowed once a year or once every two years — a common practice in Detroit, which has one of the highest proportions of vacant lots in the United States — than in lots mowed monthly or not at all.
“When we surveyed vacant lots, we found that some mowing is worse than no mowing,” said Daniel Katz, a doctoral candidate at the U-M School of Natural Resources and Environment. “This is because occasional mowing, say once a year or once every other year, creates the disturbed conditions in which ragweed plants thrive.”
Based on the findings of the two studies, the authors recommend that vacant lots in Detroit either be mowed regularly or not at all. A report issued May 27 by the Detroit Blight Removal Task Force states there are 114,033 vacant lots in the city.
“Although allowing vacant lots to reforest is controversial, it is already happening in many places across Detroit. Woody plants are establishing in vacant lots and reclaiming large chunks of Detroit,” Katz said. “Regardless of whether people think that reforestation of vacant lots is a good or bad thing overall, it will have the benefit of reducing ragweed pollen exposure.”
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