ENTOMOLOGICAL. PARIS GREEN AND LONDON PURPLE.

Otago Witness, Issue 1952, 23 July 1891, Page 8

ENTOMOLOGICAL. PARIS GREEN AND LONDON PURPLE.

There has always been a very natural prejudice against using any poison against inserts affecting fruit or vegetables used for human food for several reasons— the most prominent being in case children or careless persons should be poisoned by those means. Tbeie are also other objections, suoh as (in the oase of arsenites) destroying the foliage of the trees sprayed and injuring the ground and the grass under the trees. These are all no doubt very good reasons why great care and moderation should be used in dealing with araenioal poisons, but at the same time a considerable experience has now taught us that araenio is a very sffeotual remedy for both that very annoying pwt the oodlin moth and the numerous [ species of moths and beetles, &0,, which prey upon both our tree leaveß and fruit, and that it can be used with discretion msuoh a manner as to run very little risk of doing any injury, if only people using it will take reasonable care. There can be no doubt that Pans green has lately been used in gome places m a reckless manner, and in very muoh too large quantities, and it is surprising that more cases of serious consequences are not recorded. We hear sometimes of a strength of lib of Paris green to 50gal of water being used, and lib to lOOgal and 150 gal is a very common proportion. Miss Ormerod, in her last annual report, takes a great deal of trouble to impress upon her readers the necessity of taking great care in using Paris green, which, whatever iti advantages may.be, ia nevertheless a dangeroub and deadly poison. She particularly cautions those ÜBing it to avoid inhaling it when dry. The powder is very fine, and easily disturbed by a draught of air, and when inhaled in that way it is very dangerous, and may easily result disastrously. She reoommeijda alwaya purchasing it in small paokages, ready to be mixed with the water without the necessity of weighing. One oase is related in her report of a man who was employed to weigh out a quantity in pound lots, and whoJost his life in bo doing. The Btrength mentioned in Misa Ormerod'e report seemß to' vary from 2oz to 4oz to 40gal of water, and lib to 160 gal, or lib to 300 gal of water— the faot being that in a cold climate stronger mixtures* can be used than in a warm one, and aho in cold weather or the cooler hours of the day. Professor JRiley says that in the colder New England States (upon apple trees) a Btrength of lib to 150 gal of water can be used with perfect safety, whereas the same strength used in California will "result in a severe burning of the leaves* and that in California lib to 350galor400galof water " seems to be about right. >r There can be no doubt that it in imprudent and hurtful to use more arsenic than ia absolutely necessary for the purpose of poisoning the inseot-peat, and it is even a question whether doing so might not deter them from eating the poisoned Bubstances. , . Writing of London purple M*sa Ormerod says that Bhe has gone over masses of evidence of its usefulness in the United States, and the results of endless experiments to show whether London purple or Paris green is the best arsenical poison to use, and she seems to be clearly of opinion that whatever may be their relative values, the failures with London purple have generally resulted' from an entire absence of any knowledge of the strength of the artiole sold under that name. It appears that London purple (or arflenio of lime) is a waste product in the States, and obtainable at a nominal price, but that no care is taken to mark its strength; and therefore only in exceptional cases those using it have any idea what strength of arsenic they are experimenting with. Miss Ormerod Bays that when a retail dealer purohaseß London purple he is supposed to be furnished with an analysis, and that the person using it should be shown that analysis. The hint is a very useful one, and should be acted upon, as London purple haa several advantages over the more favourite Paris gi'een. It is lighter, more soluble, or at least more easily held in sußpention in the water, requiring very much less frequent stirring to prevent settling to the bottom, and it can be more evenly spread. It is stated that lib of London purple will go over four times the surface that lib of Paris green will, with as good an effect. But this is not borne out by some of, the most skilled of the United States economic entomologists. Mr O. W. Woodworth, of the Arkansas Experimental Station, in a bulletin lately published, details a large number of very interesting experiments with various arsenites, arriving at certain conclusions, one of which ia that where tbe plant is easily injured, and the choice is between Paris green and London purple, Paris green is better in every particular. Mr Woodworth also recommends a light spraying, and to Bpray from above, as the underside of the leaf iB the easiest to burn.; and he says that freßhly-mixed white arsenic promises to be one of the very best of the arsenites, and at the same time the oheapeat. All writerß seem pretty well agreed that the arsenio (whatever variety iB used) should not be used too strong, nor laid on too heavily. In the northern and warmer districts of New Zealand lib of Pans green to 300 gal, or even 400 gal, of water would probably be strong enough, but in the province of O»go, lib to 180 gal or 200 gal would moat probably b8 about right for the oodlin moth. Entomologist.

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