Johnson Grass

Melon, Tomato, Apple, Celery, Watermelon, Zucchini, Oranges, Cantaloupe, Bananas, Peaches

Johnson grass is one of the most aggressive and problematic plants found across Arizona, combining a severe allergy profile with genuinely destructive invasive behavior. A fast-growing perennial that can reach heights of approximately seven feet, Johnson grass is also an extremely invasive grass with worldwide distribution. First introduced to the United States as a forage crop around the 1830s, this invasive species is now present worldwide in countries including India, Australia, Turkey, and the United States.

Johnson grass is best adapted to warm, humid climates with high moisture levels, particularly thriving along irrigation canals, field edges, cultivated lands, pastures, and orchards, making Arizona’s extensive agricultural irrigation network and canal systems an ideal environment for its spread. It is commonly found along roadsides, in vacant lots, and at the margins of farmland throughout the Phoenix and Tucson metro areas.

Grass pollen is incredibly light, allowing Johnson grass pollen to travel hundreds of miles through the air, meaning exposure is not limited to those living in the immediate vicinity of the plant. While Johnson grass pollination occurs throughout the year in warm climates, it peaks from early summer through fall, placing it squarely within Arizona’s broader summer grass allergy season alongside [Bermuda grass](https://carefreeallergy.com/allergen/bermuda-grass/).

Johnson grass pollen exhibits cross-reactivity with maize, Bahia, timothy, sweet vernal, and Bermuda grass pollen, all species belonging to the same Poaceae family. This means patients sensitized to Johnson grass are very likely also reacting to Bermuda grass simultaneously, two allergens that share both season and habitat across the Valley.

Because Johnson grass is classified as a noxious weed in many states and is actively managed as an invasive species, it is never recommended for intentional landscaping. If it appears on your property it is typically the result of windborne seed spread rather than deliberate planting, and removal is generally encouraged both for allergy and ecological reasons.

If your summer and fall symptoms feel severe and difficult to manage, Johnson grass combined with Bermuda grass could be a significant factor. The team at Carefree Allergy can confirm your specific triggers through targeted testing and build a treatment plan tailored to you. Options range from medication management to long-term immunotherapy to reduce your sensitivity to Johnson grass and the other grass pollens active across Arizona each summer.