Pollen Type: Grass
Cross-Reactivity: Common Cultivated Sorghum, Sudan Grass
HS Allergy Extract: Johnson Grass
Genus/Species: Sorghum halepense
Common Names: Johnson Grass, Egyptian Millet, Evergreen
Distribution: Central California south. Southwestern and southern states; Mississippi valley states north to Kansas and Iowa. From the Mississippi eastward to the Atlantic coast. New Jersey and Pennsylvania are the northeastern limits.
Locations: Open forests, old fields, ditches, and wetlands.
Pollinating Period: July-September; June-October in warmer parts of its range.
Pollination Method: Self-pollinated; some wind-pollinated. In some warm moist regions, Johnson Grass is extensively blighted by smut, preventing pollination.
Description: Johnson Grass is a coarse upright perennial with broad flat leaf blades which grow 3’-6’ tall. The fleshy creeping rootstock enables it to spread and form dense patches. Its loose spreading heads (panicle) are typically around 12″ and are a characteristically purplish-red color. Johnson Grass spreads quickly and is considered an invasive species in many regions. It’s generally considered a widespread allergic factor. However, its pollen grain is large and not as readily airborne as most grass pollens. Because of this, Johnson Grass is considered of secondary allergenic importance.