The Worst Offenders
Seasonal allergy is caused by tree pollen in the early spring. During the late spring and early summer, the irritating pollen is usually from grasses. Weeds are the typical pollen source in late summer and into the fall.
In springtime, trees release huge amounts of pollen. Some common trees like pine, birch, alder, cottonwood, ash and cedar produce the most allergens. The lightest pollens are often the worst allergy triggers. Trees with large blooms like magnolias and dogwoods produce larger, heavier pollens. These trees depend on insects, not wind, to transport pollen. They tend to be lower in allergy potential.
Grass pollen levels are affected by temperature, time of day and rain. Ryegrass, Bermuda grass and Timothy are the worst offenders. If grass pollens bother you, it’s best to have someone else mow your lawn when possible. It’s also a good idea to keep your grass cut short.
About 75 percent of Americans who have plant allergies are sensitive to ragweed. But other weeds, including pigweed, nettle, curly dock, lamb’s-quarters, sheep sorrel and sagebrush, produce pollen allergens. Ragweed season runs from August to November.