SPOTTED KNAPWEED SEED VIABILITY AFTER PASSING THROUGH SHEEP AND MULE DEER

Spotted knapweed (Centaurea maculosa Lam.), an introduced perennial pl ant, has invaded large areas of rangeland in the northwestern United S tates. Grazing animals may disseminate the weed by transporting seeds in their digestive system and depositing them in their feces. In this study percent viability and emergence of spotted knapweed seeds that p assed through mule deer (Odocoileus hemionus hemionus) and sheep (Ovis aries) were determined. Percent viability included seeds that germina ted and seeds that tested positive with tetrazolium. In the first tria l, we pulse dosed 3 mule deer and 4 ewes with 5,000 spotted knapweed s eeds each. Seed recovered from manure collected daily for 10 days afte r dosing was tested for percent viability. We recovered 11% of the kna pweed seeds from the 3 mule deer, and 4% from the sheep. Based on high variability in (0 to 26%) percent viability of recovered seed, we tho ught that our drying the manure at 50 degrees C may have killed some o f the spotted knapweed embryos. To determine if drying at 50 degrees C affected viability, we pulse dosed 4 rams with 5,000 spotted knapweed seeds each in a second trial. One subsample of manure was washed the same day to recover seeds and then dried at 35 degrees C, a second sub sample was dried at 50 degrees C, washed, and then dried at 35 degrees C. We recovered 17% of the spotted knapweed seeds from the 4 rams. No viable seeds were recovered from manure heated at 50 degrees C, and n o viable seeds were recovered more than 2 days after dosing. Percent v iability of seeds recovered from manure dried at 35 degrees C ranged f rom 0 to 22%. In both trials, percent viability of recovered seeds was lower compared with seeds that did not pass through animals. Sheep an d mule deer can ingest, transport, and disseminate viable seeds of spo tted knapweed in their feces.