PYRETHRUM – Chrysanthemum cinerariaefolium

General

Pyrethrum is a daisylike perennial plant of the genus Chrysanthemum belonging to the Compositae family. The white flowersheads possess insecticidal properties.

Pyrethrum originated in the Dalmatian Mountains of Yugoslavia and its cultivation spread throughout the world at the turn of the century. The colonial powers introduced it into East Africa and South America and after  the First World War Japan became the principal exporter (14).

The cultivation of pyretthrum, takes place in mountainous regions up to a height of  3000 m, ideally in semi-arid conditions where the winters are cool. Rainfall of  1200 mm with a 2-3 monthh dry season are best. Pyrethrum can withstand frost down to –12°C, but in situations below about 1600 m the flowers do not set sufficiently. The content of  the active substances increases with the height and cooler average temperatures (78).

In places with humus-rich loams and heavier rainfall the plant grows more profusely, but the insecticidal content is less plentiful than when it grows in poorer, drier situations. The flowers are picked on dry, hot days when they are fully open, and left for a short time in small heaps to warm throught before being spread to dry 3-4 cm thick on mats in an airy, shady place. The harvest produces between 200 and 1000 kg per hectare (80). Pyrethrum flowers are best stored air-tight and in darkness.

Effective Range

Pure contact poison

Insecticidal, repellent, antifeedant (52).

Through its effect as a nerve poison, it produces erratic movement, excitement and finally paralysis (knock-down effect). The insects can, however, recover from the amounts required to produce the knock-down effect within 24 hours. Larger doses are needed to bring about death (141).

Target Insects

Aphids                                   - general                                (52)

Coffee bugs                          - Lygus spp.                          (78)

Colorado beetle                    - Leptinotarsa decemlineata          (52)

Flea  beetles                         - general                                (78)

Grasshoppers                       - general                                (78)

Imported cabbage worm               - Pieris rapae                         (52)

Large cabbage worm           - Pieris brassicae                           (78)

                                      - Aspodydia spp.                            (52)

                                      - Empoasca devastans                  (52)

                                      - Leucinodes orbonalis                  (52)

                                      - Ophiomyia reticulata           (52)

Pyrethrum is effective against numerous caterpillars, beetles, aphids, mites, locusts, thrips, moths etc.  ….. (35).

Espace pour photo de Pyrethrum

Remarks

The poisonous effects of Pyrethrum on warm-blooded mammals are so slight that it is usually regarded as harmless to male. However, prolonged contact wih the skin can produce a rash, and inhaling dust or spray can cause headaches and sickness (116).

The toxicity of pyrethrum preparations is considerably increased by the addition of small quantities of rotenone (e.g. derris, tephrosia, lonchocarpus) or nicotine (e.g. tobacco, anabasine) (78).

The effectiveness of pyrethrum is quickly reduced under the influence of strong sunlight (151). The addition of anti-oxidants, e.g. taneic  acid (present in annona bark) slows down this process.

Substances known as synergists such as sesame oil or piperonyl butoxile enhance the utilization of the toxic suibstances in pyrethrum either by increasing or prolonging their effects. This means that insects do not recover so quickly after the knockdown effect.

Methods of Use

  Pyrethrum is used in two ways : as a poder or dust, and as a spray. As a dust it can be used either pure or mixed with a carrier such as talc, lime or diatomaceous earth. When it is use as a spray, pyrethrum is usually dissolved in water, soap solution or kerosene. After kerosene spray has the advantage that the decomposition of the active substance is slowed down (141). Soapy sprays have some effects on the surface action and increa  the toxicity of the pyrethrum. The spray should be applied as soon as it is prepared (78).

*Kerosene-extract

500 gm pyrethrum flowers are steeped in 4 litres of kerosene       half a day. After straining through a      or cloth the so    is ready for use . It has been shown       kerosene  

*500 gm pyrethrum powder, 3-4 litres of paraffin.

The pyrethrum is steeped in paraffin for a day, stirred occassionnally and strained before use. This preparation has been       in plantations in Kenya (92).

*20 gm pyrethrum powder, 10 litres of water.

The ingredients are strirred well together and applied immediately. For the best effect this mixture should be applied in     evening (126).

*Dufour preparation

1-1,5 kg dried pyrethrum, 3 kg liquid soap and 100 litres a water are being extracted like above mentionned. The addition a soap is supposed to increase the effectivity four-fold (12).