Seed ecology of Apiaceae weeds in pyrethrum

Anthriscus caucalis M. Bieb. (burr chervil) and Torilis nodosa (L.) Gaertn. (knotted hedge-parsley) are two widely occurring weed species in pyrethrum (Tanacetum cinerariifolium (Trevir.) Sch. Bip.) crops in northern Tasmania. Little is known about the seed ecology of these two Apiaceae weed species. This study examined the level of seed dormancy of both species and their germination response to fluctuating temperatures, dark and light, stratification and planting depth. Both A. caucalis and T nodosa displayed morphological dormancy (i.e. an underdeveloped embryo) that was overcome by warm stratification. In addition, seeds of A. caucalis displayed physical exogenous dormancy that was broken by scarification and a physiological endogenous dormancy that was overcome by dry storage at 20°C. More than 90% of freshly collected, mature seeds ofT nodosa germinated within 14 days of imbibition at 20°C. Optimum seed germination temperature was between 6°C and l5°C for A. caucalis and between l8°C and 23°C for T nodosa. Optimum seed burial depth for seedling emergence was between 0 and 30 mm for both species, with emergence reduced at 50mm and prevented if seed was planted at 70mm. Removal of a light stimulus was found to restrict the germination of A. caucalis and T nodosa. The results of this study provide valuable information for the development of an effective integrated weed management strategy for control of these weeds in pyrethrum.