METHODS OF CYANIDING IN GLASSHOUSES.

New Zealand Journal of Agriculture, Volume 48, Issue 1, 20 January 1934, Page 47

METHODS OF CYANIDING IN GLASSHOUSES.

ECONOMICAL CONTROL OF WHITE-FLY. J. Muggeridge, Entomologist, Plant Research Station, Palmerston North. The most economical way of dealing with infestations of white-fly in glasshouses (Speyer, 1929), apart from biological control methods, is by fumigation with hydrocyanic (prussic) acid gas. The gas is generated by dropping one part by weight of sodium cyanide (98 per cent, purity) into glass jars placed at regular intervals upon the paths of the house, each jar containing 4-J- parts by volume of 33 per cent, sulphuric acid. One-fifth to one-quarter of an ounce of sodium cyanide gives off a quantity of gas into a space of 1,000 cubic feet sufficient to kill all the adult flies and about 90 per cent, of the scale stages, but the eggs are not killed. A second fumigation is therefore necessary from a fortnight in warm to three weeks in cool weather after the first.

’One-quarter of an ounce of sodium cyanide to the 1,000 cubic feet space is the maximum which can be used with safety upon most glasshouse plants, and as the gas is easily decomposed in the presence of light it is essential to start fumigation at dusk, and to air the houses thoroughly by opening the doors and ventilators at dawn. While no further precaution than the latter is called for in the case of plants with coarse or leathery foliage, the tender foliage of the tomato plant will not stand, without grave injury, concentrations of the gas sufficient to kill the scale stages of the insect, unless water is withheld from the roots for a considerable time before fumigationthat is to say, the plants to. be fumigated must actually require watering when fumigation is started. Moisture upon the foliage, however, is of no concern. Cucumber and allied plants which require water continuously will not stand fumigation with a greater concentration of gas than is obtained from | oz. of sodium cyanide to the 1,000 cubic feet space, an amount sufficient only to kill a good proportion of the adults, the eggs and scale stages being left alive.

Though prussic acid gas is extremely poisonous to man, there is no danger from the practice of cyaniding provided ordinary precautions are taken. The sodium cyanide should never be wrapped in paper or cardboard before being dropped into the acid. The ventilators should be closed and a door left open ; the cyanide charge is then dropped into the acid, and the operator leaves the house comfortably, closing and locking the doors. On opening up at dawn the ventilators should first be opened from outside, but if this is not possible, the door or doors should be opened for twenty-five to thirty minutes before any attempt is made to enter the house to open the vents from inside. It is inadvisable to fumigate on windy nights, as the gas is liable to become very unevenly distributed. The Dry Method. The foregoing method, which is usually referred to as the jar method, is now apparently largely superseded by the dry method or

slow process generation of hydrocyanic acid gas. Directions for the adoption. of this method are as follows : —

Dry powdered sodium bicarbonate and high-grade sodium cyanide (98 per cent, purity) in a fine state of division, are thoroughly mixed together in proportion of three parts sodium bicarbonate and one part sodium' cyanide by weight.

One ounce of the mixture to every 1,000 cubic feet space , is distributed upon the paths of the houses, which must be dry. As the generation of cyanide is slow, the operator can treat a considerable number of houses in a block single-handed.

The . mixture should not be touched with the hands ; when distributing, it should be shaken from a large tin, the operator walking backwards to avoid getting the powder upon his clothing. The ventilators may be opened during distribution, and closed immediately after. The houses should be locked up for the night.

The mixture should be distributed at dusk, water having , been withheld from the plants, so that they require moisture at the root. Fumigation on rainy, but. not necessarily on windy, nights is to be avoided. The ventilators should be opened from outside at dawn the next morning, and left open for not less than one hour. The residual sodium carbonate may be left on the paths. Heat may be put on during fumigation if conditions demand it.

APPOINTMENT OF DIRECTOR, LIVE-STOCK DIVISION.

Consequent upon the retirement of Mr. J. Lyons, Mr. W. C. Barry, M.R.C.V.S., has been appointed Director of the Live-stock Division of the Department of Agriculture. For nearly the past eight years Mr. Barry has been District Superintendent of the Department for the Wellington District, which includes Wellington, Hawke’s Bay, Taranaki, Marlborough, and Nelson. Mr. Barry came to New Zealand in 1915 as a Government Veterinarian and was first stationed at Christchurch with supervision over some of the Canterbury meatworks and the milk-supply of the City of Christchurch. During the war he was engaged in active service with the New Zealand Expeditionary Forces m Egypt as a Captain in the Veterinary Corps, and on repatriation resumed his former activities in Christchurch. For some time he was lecturer on veterinary science at Canterbury Agricultural College, Lincoln. In 1921 Mr. Barry proceeded to Auckland to fill a vacancy in the Department’s veterinary service, and acted in the capacity of District Superintendent at Auckland for a few months prior to his transfer to a similar position in Wellington early in 1926.

Noxious Weeds Order. The Waitomo County Council has . declared hemlock (Conium maculatum) to be a noxious weed within its jurisdiction/ The reappointment by His Excellency the Governor-General of Mr. C. H. Hewlett as a member of the Board of Governors of Canterbury Agricultural College, is gazetted. Special Orchard-tax payable in the Rangiora Fruitgrowing District. By order issued in exercise of the powers conferred by subsection (3) of section 4 of the Orchard-tax Act, 1927, it is provided that, in addition to the general orchard-tax payable under section 3 of the said Act, the occupier of every orchard within the Rangiora commercial fruitgrowing district shall in each year be liable to pay a special orchard-tax calculated at the rate of 2s. for every acre or part of an acre comprised in his orchard and planted with apple-trees, pear-trees, or quince-trees.