LEAFLETS FOR FARMERS, NO. 25.

New Zealand Mail, Issue 1217, 28 June 1895, Page 7

LEAFLETS FOR FARMERS, NO. 25.

New Zealand Department of Agriculture. John D. Ritchie, Secretary.

SOME POTATO DISEASES, AND HOW TO PKEVENT THEM.

By T. "V.r. Kirk, F.L.S., &c, London. During the past season North Island potato-growers have sustained severe loss through the attacks of fungus and insect pests, especially the former. The descriptions in this leaflet are necessarily brief, but the following will prove sufficient for all practical purposes.

The most serious of the diseases abovementioned i«* Macrosporium solani, a fungus which attacks the foliage. It first appears on the older leaves in the form of small brown or greyish-brown spots, which gradually spread and join, so that soon a considerable area is involved, the affected parts becoming; curled, hard, and brittle, while the remainder frequently assumes an unhealthy yellowish colour. i On the appearance of the disease the tubers cease to grow. Usually in about three weeks most of the leaves are dead; the stems remain green for some time longer, and then gradually perish. The tubers, being undeveloped and unripe, turn soft and will not keep. The crop in some portions of the North Island has also suffered from the depredations of the potato-moth, described in Leaflets for Farmers No. 15; but this year it appears to have been more plentiful than usual in the vines, and has done considerable damage by eating out the pith. There can be no doubt that in some districts this insect has been blamed by farmers for the havoc worked by, the Macrosporium, because, on examination, they found the grubs, but did not observe the' tiny fungus which was the principal Cause of the trouble. The remedy for or rather the preventive of this Macrosporium, and, indeed, of other potato diseases of fungoid origin, is * Bordeaux Mixture; to which, where insects such as the bronze beetle or potatomoth attack the foliage or stem, a little Paris green should be added, as follows : 41b sulphate of copper 41b fresh lime 4oz Paris green 31b common treacle 45 gallons water

Dissolve the copper in, say 5 gallons of water in a wooden vessel: the best way is to tie it in a loosely-woven bag, and suspend the bag from a stick laid across the tub ; or, if in a hurry, use hot water. Slack the lime in another vessel, and add it to\ tha copper solution; stir well till thoroughly mixed, then add sufficient water to bring the whole up to 45 gallons. Now strain out any dirt; then s,tir in the treacle. Mix the Paris green to the consistency of thin paste, and add it to the mixture, stirring well. Apply with a proper spray-pump with a cyclone nozzle: first, when the potatoes are between 6in and 9in high, and twice

later' at intervals of about ten days. Repeat if necessary. If the treatment above advocated is carefully carried out it will prove effectual in preventing the attacks of both insect and fungoid pests. The Bordeaux mixture prevents the germination of fungus spores, and the Paris green will poison the tiny grubs directly they hatch and begin to eat into the vine.

For plots of, say, up to 10 acres, a knapsack sprayer will be sufficient; but for extended plantations a more powerful machine will be needed, in order to cover the ground as quickly and cheaply as possible. In the case of large areas the crops should be planted sufficiently wide in the rows to allow of the passage of such an implement as the Strawsonizer. Figures and particulars regarding two kinds of spraying-machines are attached.^ It has been proved by extensive experiments both in Europe and America that spraying with Bordeaux mixture will not only prevent or keep down fungus diseases,

but will so increase the yield as to more than pay the extra expense incurred. Great care must, however, be taken in mixing and applying fungicides and insecticides.

The Macrosporium must not be mistaken for the extremely destructive " potato rot," so much dreaded in older countries. There is no doubt that it has been so mistaken both in England and America, and this mistake has given rise to reports that " potato rot " {Phytophora infestans) had broken out in various localities, when it was only Macrosporium, which, serious as it may be, is not nearly so bad as Phytojohora. ; It is very important that all old vines

should be gathered together and burned as soon as possible, in order to destroy the so reduce the risk of infection next season.

The other fungoid disease to be mentioned in this paper is " scab." The above illustrations are reproduced from photographs of potatoes grown this year in the North Island and known as the " American rose." They give a very good idea of the appearance of tubers badly attacked by this disease. The scabs are frequently in depth, and badly scabbed potatoes remind one of the appearance of a person who has suffered severely from small-pox. In some instances, as in the right-hand figure of the illustration, the disease causes the tubers to crack, the crack frequently extending as much as ijih to fin into the flesh. It will thus be seen that, though the remaining portions are sound, the market value of the crop is enormously reduced. The State Agricultural College of Michigan has proved-'—and I have verified the experiment—that if potato-seed even badly affected with " scab " be treated as follows, the resulting crop will be smooth and clean-skinned :

Dissolve loz of corrosive sublimate in 12 gallons of cold water, and mix thoroughly. This liquid must be prepared and kept in a wooden trough or tub. The potatoes may be placed in an old basket and immersed in the liquid for one hour and a half (neither more or less), then allowed to dry before planting. On no account should they be replaced in the old sacks. After drying put them into fresh baskets or boxes and cart to the field.

The preparation is poisonous, and care must be taken that neither liquid or potatoes are accessible to either animals or children.

The cut of the knapsack spray pump adjoining is from the catalogue issued by Messrs Danks and Co., of Melbourne, but there are a considerable number of makers, and their instruments vary in details, so that all tastes may be readily suited. Intending purchasers are recommended to procure a copper knapsack, in preference to one of galvanised iron. The initial cost is somewhat heavier, but the copper instrument will last longer, and is for all classes

of sprays, while if an iron tank be used with Bordeaux or similar mixture the tank will rob the preparation of much of its efficacy by extracting the copper therein contained. Price of this class of pump, about £3 10s.

The above is a drawing of the famous Bean Pump- It is a powerful instrument, well adapted for work on considerable areas. It requires to be placed on, a cart or sledge, with a cask of the mixture. Messrs A. and T. Burt, of Dunedin, manufacture an almost identical instrument in four sizes, as follows: — !No. l. ; —Intended for use in small M: s. d. orchards and nurseries. Price including suction-hose, 20ft delivery-hose, rod, three nozzles, and steam-gauge ... 710 0 No. 2.—Same size of pump with larger chamber, capable of supplying two sprays at a time 9 0 0 No. 3. —A much larger and stronger pump in every respect ... 11 0 0 No. 4. —The largest-sized pump, capable of supplying four sprays at a time 12 10 o

The above prices include steam-gauge, suction and delivery hose, spray-rod, and one each of the three different nozzles. The gauge is included in above prices, as better work is done when it is attached/} at a glance the operator knows the pressure, and when it is high the spray is more effective. If the gauge is not wanted, deduct from the list SI.

As with the knapsack, there are also numerous other makes to be had, many of them of excellent design, and intending buyers will do well to make full inquiry before purchasing. The above cuts are not intended to advocate any particular make of pump, but only as a guide, and to give a general idea of the kind of machines required.