The spring tree pollen season winds down in May. The only new trees that begin pollinating this month are black walnut and the hickories. There are several species of hickory in eastern Oklahoma including pecan (Carya illinoensis). The beginning of May still finds some oak, mulberry, and other April pollen types. Also, we begin seeing grass pollen in the air during May as many of the native grasses begin flowering. Many grasses continue to pollinate all summer and even into the fall. Weeds that begin pollinating in May include dock (Rumex sp) and nettle (Urtica).
Black Walnut (Juglans nigra)
Hickories and pecan (Carya spp.)
Grasses (Family Poacaea)
Oak (Quercus spp.)
Mulberry (Morus spp)
Hackberry (Celtis laevigata and C. occidentalis)