Background: Grass pollen is a worldwide cause of respiratory allergy. Identifying the causative species is essential, for example for choosing the appropriate immunotherapy, because not all grass allergens are totally cross-reacting, and the pollen calendars provide only a gross estimate. Phenologic analyses allow identification of the pollen release for each individual grass. Objectives: to assess, using phenologic analyses, the true flowering periods of grasses and to compare the data with the standard pollen calendar. Methods: phenologic analyses were performed of the following grasses: black grass, sweet vernal grass, common wild oat, barren brome, cocksfoot, tall fescue, Yorkshire fog, ryegrass, Timothy grass, bulbous meadow-grass, Kentucky bluegrass, and Bermuda grass. Sampling was performed every 10 days, starting in April 2009, at 50 stations distributed across Italy. The flowering phase was assessed using a stereomicroscopy-based method for the detection of spreading stamens. The official pollen calendar was used for comparison. Results: relevant differences were found between grass pollen count and effecctive flowering of the grass species. Only some species contributed to pollen peak, and a relevant pollen load for other species was also present out of the peak. Important Pooideae, such as Timothy grass, were not present during the pollen peak in northern and central Italy, and the same occurred with Bermuda grass. Conclusions: the various species of grasses release their pollen grains at different times during the pollen season, and this information is missing with pollen calendars. This may have a relevant effect on the choice of an appropriate immunotherapy.
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