ROOT-KNOT NEMATODES, THEIR INFLUENCE ON THE YIELD COMPONENTS OF PYRETHRUM AND THEIR CONTROL
Pyrethrum (Chrysanthemum cinerariaefolium Vis.) is widely grown in the highlands of East Africa and almost all of the crop is infested with root-knot nematodes. The multiplication method of division of the rootstock has undoubtedly enhanced this condition. Similar observations were made in the Congo and Delhaye (1968) observed a yield decline, varying with different clones, which he imputed to root-knot nematodes. Pyrethrum in Kenya seems to be almost exclusively infested by Meloidogyne hapla Chitwood and from several identifications, only one plant was found to harbour also Meloidogyne javanica (Treub, 1885; Whitehead and Kariuki, 1960).
The crop is grown for the extraction of insecticidal pyrethrins from the flowers which are harvested every two or three weeks during most of the year and then dried. The yield of pyrethrin is assessed on the fresh flower yield, the dry matter content of the flowers and the pyrethrin contents of the dry flowers; flower size has a bearing on the picking costs.