Dallisgrass (Paspalum dilatatum
) is a leafy, tufted, moderately-sized perennial grass that is native to South America. It has been introduced to tropical, sub-tropical and temperate regions worldwide for its use as pasture grass and for golf courses. Dallisgrass forms loose bunches that grow from prostrate with erect tips to completely erect.
- Height: up to 5 ft
- Stem: Compressed sheath; often tinted red with age.
- Leaves: Rolled in the bud; lack auricles; hairless, except for a few long silky hairs in the collar region.
- Flowerhead: Terminal stalk; raceme that has 3 to 5 finger-like, broadly ovate, green or purplish spikes that arise from different points along the stem and often droop; each spike contains 4 rows of spikelets that are covered with black silky hairs; bloom from May through November.
- Root: Fibrous and short rhizomes.
- Look alikes: tall fescue (Festuca arundinacea), crabgrass (Digitaria spp.), goosegrass (Eleusine indica), and knotgrass (Paspalum distichum)
Dallisgrass seedheads are susceptible to contamination with the ergot fungus, Calviceps paspali
, that is toxic to horses if ingested, resulting in a syndrome known as ergotism
. Infected seedheads develop a sticky sap-like material and appear as gray to black swellings which look similar to little popcorn. The main toxins produced by the fungus are tremorgenic alkaloids, specifically paspalinine, and paspalitrem A and B.
Dallisgrass poisoning cases in animals are often referred to as dallisgrass or paspalum staggers
. The fungus is most often found in dallisgrass seedheads anywhere from late summer throughout the fall. Cases of poisoning in horses tend to occur in parallel with the predominate growth months of the fungus.
Horses that ingest infected dallisgrass will begin to develop neurological symptoms which include trembling of the head and major muscle groups, act aggressive or overly spooky, and show jerky uncoordinated movements. Often when affected horses are startled, they fall in unusual positions.