A study of the biology and control of Anthriscus caucalis and Torilis nodosa in pyrethrum
Creators: name: Rawnsley, Richard
Publisher: name: University Of Tasmania
Year: 2023

description: The Tasmanian pyrethrum industry has been operating on a commercial basis for 23 years and is now the second largest producer of pyrethrum (Tanacetum cinerariaefolium L.) for natural insecticides in the world. The industry, with a annual farm gate value in excess of $7 million, makes a significant contribution to the rural economy of Tasmania (Australia). Currently, production involves 120 contracted growers and 1300 hectares of land. To maintain its position as a world leader in the production of pyrethrum, the Tasmanian industry must continue to improve production technologies and efficiencies. An emerging area of concern is the management of weeds, with some weed species in pyrethrum being particularly difficult to control. This includes weeds that are commonly found in vegetable crops which are grown in rotation with pyrethrum as well as relatively uncommon species; such as Anthriscus caucalis and Torilis nodosa. This study investigated the biology and control of both A. caucalis and T. nodosa which belong to the Apiaceae family. A morphological examination highlighted easily distinguishable characteristics for the identification of these relatively unfamiliar species. Anthriscus caucalis seedlings are identifiable by their tri-pinnate compound leaves which are glabrous on top with scattered hairs beneath. The fruit of A. caucalis is ovoid in shape and 2.5 to 3.5mm in size with distinguishing hooked spines and a short beak. The pedicels have a ring of hairs at the top. Torilis nodosa seedlings are identifiable by their deeply bi-pinnate compound leaves and narrow linear lobes. The fruit of T. nodosa is ovoid in shape and 2.5 to 3mm in diameter and composed of 2 distinct dimorphic mericarps. The outer mericarp has barbellate spines with the inner mericarp tuberculate. A survey of pyrethrum crops revealed that the occurrence of these species was high, occurring in 30% of pyrethrum crops, with A. caucalis being the more prevalent species. As pyrethrum is a perennial crop which can be grown for up to five years, it was also found that the frequency of occurrence of Apiaceae species increased with increasing crop age. Investigations into the germination characteristics of A. caucalis and T. nodosa revealed that A. caucalis possessed an innate seed dormancy which was overcome by seed scarification and dry storage at 20¬¨‚àûC. Torilis nodosa displayed no innate seed dormancy. Both species, A. caucalis and T. nodosa, were found to behave predominantly as winter annuals, germinating in autumn and over wintering as small rosettes. Studies indicated that T. nodosa has a transient to short term persistent seedbank, while A. caucalis has a short to long term persistent seedbank. Anthriscus caucalis was found to undergo rapid vegetative stem development during late winter early spring with flowering commencing during mid spring. Seed maturation occurred in early summer. Tori/is nodosa was found to produce procumbent stems in mid to late spring and flower approximately 6 weeks later than A. caucalis with seed maturation occurring in mid to late to summer. Studies into the chemical control of A. caucalis and T. nodosa identified a small number of herbicides with potential for use in pyrethrum. Applications of dimethenamid at 3.6 kg/ha provided the most selective pre emergent control for both species, while clomazone applied at 120.0 g/ha provided very effective control of T. nodosa. Imazamox applied at 34 g/ha provided significant post emergent control of both species with excellent selectivity for use in pyrethrum. A number of other herbicides were identified as having activity on A. caucalis and T. nodosa, however lower levels of selectivity limited their potential adoption for use in pyrhethrum. This thesis has provided significant information to the pyrethrum industry on the biology and competitive nature of the relatively unknown weed species A. caucalis and T. nodosa. The thesis has also provided immediate short term weed control strategies and enhanced the weed management options available for the industry.