CHECKING THE POTATO BLIGHT.

Otago Witness, Issue 2895, 8 September 1909, Page 7

CHECKING THE POTATO BLIGHT.

MR T. W. KIRK IN TASMANIA. Mr T. W. Kirk, the Government entomologist, who visited Tasmania at the request of the Tasmanian Government in connection with the presence the,re of blight among the potato crops, was interviewed by tho Hobart papers. Ms Kirk's views as to the value of spraying should now be well known to New Zealand potato-growers, but unfortunately many of them have paid little or no attention to his advice, with tho result that they have not only sustained losses themselves, but have been the means of infecting the crops of their neighbours. In replying to a question at Hobart as to the cost of several successive sprayings of crops Air Kirk said < — "Five" shilling to 5s Qdper acre, with a big machine. Of course, if a man only uses a knapsack sprayer over a good-«ized paddock it costs morel Often a grower does not start spraying until the disease has got 4 * good hold,, and that is another mistake made.' Spraying is to be looked upon as a preventive measure, and accordingly the first spraying 'must be applied before any disease appears. It is also important to use the propetr spraying nozzle, which is the ' Cyclone' nozzle, with which the under surface of the leaves is reached." At what period of growth is the first; spraying done? — "When the potato haulms are between six and nine inches high, and again when in^flower If the disease is bad, and the weather wet, it is necessary to spray oftener, at intervals of about ten days. Should rain fall within three or four hours after spraying it will,- of course,* be necessary to repeat the dressing as soon as possible. If this treatment is carefully carried out it will prove effectual in preventing attacks of Irish, and early blights, and will reduce most other fungoid diseases, as Bordeaux mixture prevents the germination of fungus 6pores. It is very important t« spray all potato crops whioh do not appear to have contracted the disease in a district where disease is found. Such spraying* should be looked upon as an insurance, policy. It prevents disease." Asked what are the other remedial measures, if any, Mr Kirk said that some varieties of potatoes resisted the disease more than others. Seed potatoes should be procured from clean districts, andf should ba stored in. a perfectly dry and well-ven-tilated shed. The dipping of seed potatoes in Bordeaux mixture, using the 4—4 — 40 formula, or, if the skin is well hardened, the 6—6 — 4—404 — 40 strength, is to be recommended, if done before storing. Thia dipping kills only the spores and those portions of the fungus thp.t are on iho eurface of the potato, but it is quite ineffectual in destroying the part which winters in the tissues of the tubsr itself should the fungus have already obtained admission. It is, therefore, important to sort over the tubers- from timo to time, and remove any showing the least sigr of rot. Wide cultivation is important. This enables one to cover the seed with a good depth of soil, and renders them muoh leas liable to be affected, even though the foliage may suffer severely. It prevents , the spores of the fungus being carried dowr by rain and other agencies on to the tubers. Only manures known not to encourage the disease should be used. Highly nitrogenous manures, such as nitrate of 6oda, blood, etc., help the contracting of disease, while, on the other hand, wher> the manure used is potash 6alts and phosphates the crop often escapes the disease (o a great extent. Good drainage is another important point The disease is aided by moist suTrqiindings. The addition of large quantities of lime to the soil will render crops grown on over-moist soils less susceptible to attack. The disease spreads on to healthy plants during the summer only by means of spores, which are blown about in immense numbers from affected plants, and can within an almost incredibly short tirae infect very large areas. •V single infected tuber planted in a crop oan serve as an infection centre for a whole district, so that it can easily be what danger attends the planting of diseased sets. If the disease existed within tubers apparently sound in appearance, a layman could not detect it; but if there were suspicious appearances about any of the tubers, planting should be deferred until specimens had beea 6ent to the entomologist for hie report, i