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Birches in the genus Betula are among the most recognizable spring-pollen trees in North America. For allergy sufferers, they matter because birch pollen is lightweight, readily airborne, and strongly associated with classic spring hay fever. In the United States, the biggest wild-birch exposure zones are the Northeast, Great Lakes, Upper Midwest, Alaska, and mountain West, but the birch story does not stop there. River birch extends the genus well into the Mid-Atlantic, Southeast, lower Midwest, and parts of south-central states, so birch-related exposure can appear outside the colder northern forest belt many patients expect.^1-3

Cincinnati also remained very high for grass pollen, while South Central readings held high around Oklahoma City, Tulsa, and Waco and Puerto Rico remained active for both grass and trees. Tree pollen has become more localized than earlier in spring; weeds were mostly quiet, but mold rose in Chicago, St. Louis, and San Antonio.

Grass pollen season started in earnest last week across a broad swath of the U.S., especially in the South and West, while the Midwest and Northeast still suffer from high tree pollen levels.

Spring tree pollen is now a national story: elevated readings stretched from Wisconsin and Nebraska to New Jersey, Kentucky, South Carolina, Alaska, Washington, and Puerto Rico. Grass became a big new irritant, with more high readings in the South Central, Southeast, Northeast, and parts of the West, while weeds and mold were mostly limited exceptions

Tree pollen is still the biggest allergy problem for many readers, especially in the Midwest, Puerto Rico, and parts of the South Central region. The Midwest remains the broadest mainland trouble spot: five of seven current stations reached High or Very High tree pollen, with La Crosse still in the top band and Chicago, Greenfield, Madison, and Omaha also elevated.

Tree pollen is still the main burden for allergy sufferers, with the Midwest and Southeast carrying the most widespread elevated conditions. All eight current Midwest stations reached High or Very High tree pollen, and six of eight Southeast stations reached High. South Central tree pollen is less uniform but still active, with four of seven current stations elevated.

Hornbeam (Carpinus) and hop-hornbeam (Ostrya) are not the loudest tree-pollen story in North America, but they still matter to allergy sufferers because they belong to the same birch-family branch of the spring Fagales pollen season that includes alder, birch, and hazel.^1-7 In the United States, their combined outdoor range stretches across much of the eastern deciduous forest and then reappears in smaller canyon and mountain pockets of the Southwest.^1-4

Tree pollen is still the main problem for allergy sufferers this week. The worst current tree pressure is in the Southeast, where six of seven reporting stations reached High, and in the Northeast, where all four current stations did the same. The Midwest also remains firmly in tree season, with all six current stations at that level as well.

Tree pollen remained the main burden for allergy sufferers. The heaviest pressure was in Texas and Oklahoma, where seven of eight reporting South Central stations were still High or Very High, with the sharpest strain around Oklahoma City and San Antonio. The Southeast looked nearly as difficult, with seven of eight stations also elevated, led by Tampa and the Washington, D.C., suburbs. The Midwest stayed firmly in season as well, even though a few Wisconsin sites trended lower from last week.

Alders in the genus Alnus are common wetland, riparian, and cool-climate trees or shrubs across large parts of North America. For allergy sufferers, they matter because alder is one of the earlier tree-pollen sources of the year, especially in the Pacific Northwest, coastal Alaska, the Great Lakes, the Northeast, and streamside habitats in the East and Southeast.^1,2

Maple trees in the genus Acer are among the most widespread deciduous trees in temperate North America. Across the United States, Canada, and Puerto Rico, maples are common in forests, parks, and residential landscapes, making their pollen a regular component of the early-spring airborne allergen environment. The genus contains roughly 110–120 species globally, with about 12–15 native species in North America and several additional ornamental species planted widely in urban landscapes.¹