  == Pecan trees release highly allergenic pollen grains that cause hay fever and asthma  PMID 8729670  ==  PMID 8729670   The importance of the pecan tree pollen in allergic manifestations. Clin Exp Allergy.  1996 Mar;26(3):323-9.  Rachmiel M, Verleger H, Waisel Y, Keynan N, Kivity S, Katz Y.  Pulmonary and Allergy Institute, 'Assaf-Harofeh' Medical Center, Zerifin, Israel.   ...   CONCLUSION: Pecan tree releases highly allergenic pollen grains, which are correlated to the incidence of hay fever in the exposed population. The contribution of pecan tree pollen to the symptoms was highly significant after discounting olive and cypress trees that also pollinate in the spring. In children, the pecan tree constitutes a possible etiologic agent for the development of asthma.