A newly released study by the USDA confirms what many allergy sufferers may have suspected. "Ragweed pollen in some parts of the northern United States and Canada now lingers almost a month longer than it did in 1995, and these increases are correlated to seasonal warming shifts linked to climate change dynamics in the higher latitudes, according to a study published Monday in the Proceedings of the National Academy of Sciences." Looking at ten locations along a north-south transect from Austin, Texas to Saskatoon, Saskatchewan, Canada, researchers found that from 1995 to 2009, as the number of frost-free days at higher latitudes increased, the ragweed pollen season lasted from 13 to 27 days longer.
Ragweed (Ambrosia artemisiifolia) is a native, warm-weather annual found throughout North America, usually in sunny sites. It can crowd out garden plants, plus wind-borne ragweed pollen is a big contributor to seasonal allergies. Learn to recognize the deeply cut leaves, and pull young plants from moist soil or spray them with an organic herbicide containing acetic acid or clove oil. Seedlings also can be cultivated into submission with a sharp hoe. Mature plants produce slender upright flower spikes that resemble candelabras. Cut down ragweed plants that have set seeds, then bag and dispose of the tops to reduce reseeding.