Sudan Grass Pollen Allergy: Symptoms, Causes, and Treatment Options

Sudan grass (Sorghum x drummondii) is a cultivated annual grass that is a direct hybrid between Johnson grass (Sorghum halepense) and grain sorghum (Sorghum bicolor). It was developed as a fast-growing summer forage crop for livestock, combining the rapid growth and drought tolerance of its wild Johnson grass parent with the palatability characteristics of grain sorghum. In allergy terms, the parent-hybrid relationship is clinically significant: Johnson grass has five characterized WHO/IUIS allergens (Sor h 1, 2, 7, 13, 23), and sudan grass as its direct hybrid is expected to carry homologous proteins — particularly the Group 1 major allergen Sor h 1. A patient sensitized to Johnson grass should expect to react to sudan grass pollen through shared Panicoideae allergen proteins.

Yes. Sudan grass allergy is treated with Johnson grass representative extract because no dedicated sudan grass pollen extract exists for clinical use. The direct genetic relationship between sudan grass (Sorghum x drummondii) and Johnson grass (Sorghum halepense) provides the strongest scientific basis for this approach: the allergen proteins expected in sudan grass pollen are the same Sor h 1 Group 1 beta-expansin homologs that drive Johnson grass sensitization. Johnson grass extract is available as a non-standardized clinical product (ImmunoCAP g10) for both skin prick testing and immunotherapy formulation. Bahia grass (Pas n 1) is a second Panicoideae option. Neither FDA-approved SLIT tablets (which cover only Pooideae grasses) nor timothy-based extracts are appropriate for sudan grass allergy.

Timothy grass (Phleum pratense) belongs to subfamily Pooideae — the cool-season sweet grass group — while sudan grass belongs to subfamily Panicoideae — the warm-season sour grass group. Although both are members of the grass family Poaceae, these two subfamilies have different major allergen profiles. Pooideae grasses possess Group 5 allergens (ribonuclease-like proteins) that are absent in Panicoideae grasses entirely. The FDA-approved SLIT tablets Grastek and Oralair contain timothy and Pooideae extracts specifically designed to address Pooideae sensitization — they provide no meaningful desensitization for Panicoideae allergens. A farmer with sudan grass allergy who receives only timothy immunotherapy will continue to experience summer symptoms from their forage crops because the wrong subfamily is being treated.

Sudan grass pollen exposure in agricultural settings can exacerbate asthma and potentially contribute to new-onset occupational respiratory sensitization in farmers who work with this forage crop regularly. Livestock farmers who grow sudex or sudan grass for hay face prolonged, high-concentration Panicoideae pollen exposure during July–September — including the concentrated bursts that occur during mowing and baling operations that mechanically disturb flowering plants. Workers with atopic predisposition who develop new summer asthma after beginning sudan grass cultivation or after moving to farms where sudex is grown should request formal occupational allergy evaluation. Documented sensitization to Johnson grass (the allergen reference for sudan grass) would support an occupational exposure connection.

Sudan grass pollinates from July through September, with peak production during the hottest weeks of July and August when C4 warm-season grasses are most physiologically active. The season begins after Pooideae cool-season grasses (timothy, bluegrass, ryegrass) have peaked in May and June, extending the total grass pollen burden in agricultural regions through the heart of summer. Importantly, sudan grass is a cultivated annual sown deliberately each spring, meaning farmers can anticipate the pollen season based on their planting calendar — approximately 60 days after planting, plants enter bloom and begin pollinating. Multiple-cut sudex systems create repeated bloom cycles through the season as each cut field regrows and re-enters pollination.

Sorghum-sudan hybrids (commonly called sudex, sudangrass hybrids, or BMR sorghum-sudan) are bred from the same parental combination as traditional sudan grass — Sorghum halepense (Johnson grass) x Sorghum bicolor (grain sorghum) — with selection for specific traits like higher yield, lower prussic acid content, or brown mid-rib genetics for improved digestibility. From an allergy perspective, sudex hybrids would be expected to carry essentially identical Panicoideae allergen profiles to traditional sudan grass, given the shared genetic parentage. The clinical approach — testing with Johnson grass extract, treating with Johnson grass or bahia grass immunotherapy — applies equally to all sorghum-sudan and sudex hybrids grown as forage crops.

Sudan grass and ragweed both peak in August and September and produce clinically indistinguishable hay fever symptoms — sneezing, runny nose, itchy eyes, and nasal congestion. The only reliable way to distinguish them is allergy testing. A positive Johnson grass IgE test (or Sor h 1 component) confirms Panicoideae grass sensitization consistent with sudan grass exposure. A positive Amb a 1 result confirms ragweed sensitization. Many agricultural patients in central and southern states have both simultaneously, given that ragweed also thrives in disturbed agricultural soils alongside sudan grass fields. Distinguishing the two matters because immunotherapy uses completely different extracts: Johnson grass for Panicoideae grass, short ragweed for Amb a 1. A combined panel at your allergist visit resolves the question efficiently.

Sudan grass is cultivated primarily in the central and southern United States where hot summers favor C4 warm-season grass growth — Texas, Oklahoma, Kansas, Missouri, Alabama, Tennessee, Mississippi, Georgia, and the Carolinas are the primary production states. It is also grown in irrigated western agricultural regions including parts of California, Arizona, and New Mexico. Sudan grass is not a weed that colonizes all states like Johnson grass or barnyard grass — it is a cultivated crop that grows only where it is deliberately planted. Its US distribution is therefore determined by agricultural practice rather than ecological spread, meaning exposure is concentrated in livestock-farming regions rather than uniformly distributed. Johnson grass (the parent species), however, IS a widespread invasive weed in all southern and eastern states.

Yes, although agricultural workers face the highest exposure, sudan grass allergy can develop in non-farmers living near agricultural operations. Rural residents whose homes adjoin livestock farms growing sudex or sudan grass for hay are exposed to summer pollen from adjacent fields during the July–September season. Wind can carry Panicoideae pollen from active agricultural fields significant distances into nearby residential areas. Additionally, Johnson grass — the parent species of sudan grass — is a common invasive weed along roadsides, railroad rights-of-way, and field margins throughout the southern and central US, providing Panicoideae sensitization exposure even for non-farmers. A patient sensitized to Johnson grass through non-agricultural roadside exposure would have the same cross-reactive IgE that responds to sudan grass pollen.

No FDA-approved SLIT tablet covers Panicoideae grass sensitization, including sudan grass allergy. The three FDA-approved grass SLIT tablets — Grastek (timothy), Oralair (five-grass mix), and Ragwitek (ragweed) — address Pooideae grasses and ragweed only. Panicoideae grasses like sudan grass, Johnson grass, and bahia grass are not covered by these products due to the different allergen profiles of the sour grass subfamily. The practical immunotherapy options for sudan grass allergy are: custom-compounded SLIT drops with Johnson grass or bahia grass extract (off-label, but with strong evidence from European SLIT trials), or subcutaneous immunotherapy (SCIT) shots with Johnson grass extract. Both require prescription from a board-certified allergist with experience identifying and treating Panicoideae sensitization.