PLANT EXTRACTS

Manawatu Standard, Volume LV, Issue 246, 14 September 1935, Page 14

PLANT EXTRACTS

WARNING TO GROWERS

MYCOLOGIST’S ADDRESS,

An address on “Plant Extracts as Sprays” was given by Dr G. 11. Cunningham, Dominion mycologist at the Plant Research Station at Palmerston North, at the Dominion conference of the New Zealand Fruitgrowers’ Federation, Ltd., on Thursday. Certain plant extracts, he said, were among the most promising insecticides. Several had proved to be both stomach poisons and contact’ insecticides. As they did not injure plant tissues, left no apparent deposits on leaves and fruits, and were (save nicotine) 11011-toxic to warm-blooded animals, they were preferable to arsenates and oils. In all probability they would ultimately replace those in the spray calendar. Although its insecticidal value had been known since 1746, it was not until stablo extracts were placed on the market that nicotine had become popular as a spray. Commercial preparations were concentrated extracts secured by distillation of leaves of tobacco. Two species of tobacco were used as nicotine sources, commercial tobacco and Turkestan tobacco. Nicotine was an effectual contact insecticide for control of soft-bodied insects. The vapour was tlie effectual agent; consequently in spraying it was necessary to apply sufficient to maintain a lethal concentration of vapour in the region of the insect and to apply the material under conditions that ensured ready volatilisation. With certain strains of nicotiana rustica produced at the Blunt Research Station the nicotine content was so high (up to 15 percent.) that growers could well use this for preparing their own nicotine sprays. Dr Cunningham also .discussed extracts of pyrethrum. The insect powder was prepared * from powdered flower heads of two species of chrysanthemum, he said. Unfortunately it was not yet possible to recommend the use of extracts as sprays with any degree of confidence, owing to the difficulty of procuring a stable and standard product which might be held and used as required. Certain plant evtracts which had shown a high degree of toxicity were those secured from tropical plants used by the natives as fish or arrow poisons. “It is evident that botii pyrethrum and fish poison extracts are valuable insecticides,” Dr Cunningham said. “But their use cannot yet be recommended ; partly because we know so little about their toxic properties toward different insects; principally because of the difficulty of securing at present extracts of known composition which will remain stable when held for any time.

“I stress this fact as it may be several years before materials are available in such form that they may be used with the certain knowledge that they will give satisfactory results.”