(Minnesota, Wisconsin, Michigan, Iowa, Missouri, Illinois, Indiana, Ohio)

In the Great Lakes region, allergy-provoking trees pollinate from March to June. The most common allergy-causing trees in this region are the elm, maple/box elder, alder, birch, oak and hickory. The oak tree may continue pollinating until mid-June.

Many grasses pollinate in this region during the summer, from May to July. Starting in May, redtop, brome, orchard grass, fescue, rye, Bermuda and timothy pollinate.

Weeds generally pollinate from July to September, including ragweed, plantain and nettle. Other allergy-causing weeds in the region include the waterhemp, lamb's-quarter, pigweed, Mexican fire bush and Russian thistle. Later in the season, hemp can cause problems for allergy sufferers – typically from mid-July to mid-August. Then, from early August until late September, ragweed pollinates in this region.