Potato Diseases.

Ellesmere Guardian, Volume XXIX, Issue 2728, 27 January 1906, Page 3

Potato Diseases.

(By T. W. Kirk, F.L.S.) Potato-growers have suffered most serious loss during the past season. . The area under potatoes m 1903 — 4 \ was 31,778 acres, m 1904—526,331 acres, showing a decrease of 5,447 acres. Disease has reduced the yield by fully 2 tons per acre, which equals 52,662 tons, which, at only per ton, means a direct loss of 986. That spraying with Bordeaux I mixture, if properly done, is thoroughly effectual is proved by the following: — . Last November I arranged to have a paddock of ij acres at Otahuhu, belonging to Mr Nicholls, sprayed by Mr Simras, one of the staff of the ; Division of Horticulture. The disease had got a fair hold on the crop. The following is Mr Nicholls's letter:— Otahuhu, Bth March, 1905. (Sir, — When you first sprayed our potatoes the disease had a firm bold on the plants. This was more noticeable m about six rows, which were far more advanced than the rest, on t account of being sheltered from the I wind by a furze hedge. When these 1 were sprayed they were m a bad [estate, for most of the' leaves were .r dead ; the spraying of these Was not ■r? effective as the rest, because they were too far gone, and when we started digging we found about 25 per cent, affected. The rest of the potatoes we left till after the spraying was finished, for about six weeks before digging, and m these we found only about 5 per cent, affected This proves that, if the potatoes are spray ed when the disease is m its earliest stages, spraying is completely sueI cessfui. The size of the plot was i£ acres, and it yielded 6£ tons of sound potatoes. I think the crop would ■■' have been far heavier if the ground had been tilled better, because most of the paddock had a large amount of "twitch m the soil. — Yours, &c , L. Nicholls. The following, from Professor I Marshall Wards "Diseases m Plants," gives a good account of the history of this disease: — In 1844 and 2845 the potato-disease assumed an epidemic character so appalling • m its effects that it is no exaggeration to say it constituted a national disaster m several countries. It was .: stated at the time that the disaster had been known for some years m Belgium, Canada, and the United States, m Ireland, and m the Isle of :"Thanet, and m other parts of the I world. Similar, but less devastating I epidemics have occurred since. It I was generally noticed that the plants I themselves were full of foliage, surI charged with moisture, and of a I luxuriant green colour, promising I abundant crops. The now wellI knbwn spots, at first pale and then ■ brown, fringed with the pale whitish ■ mould-like growth — the conidioI phores of the Phytophthora — were I observed during the dull, cloudy, I and wet weather, when the atmosK^phere was saturated for days togeB^ther m July and August. The act- ■ ual amount ot rain does not appear ■ to have been excessive, but most obI servers seem to agree that dull I weather with moist air had succeedI ed a warm, forcing period of growth. B §o. rapidly did the disease run its ■ course, that m a few days nearly all ■ the plants were a rotten, blackened H mass m the fields, and the potatoes ■ dug up were either rotten or soon ■ became so m the stores. Further H experience has confirmed this, and Hwe now know that the epidemic is ■very apt to appear m any region ■where potatoes are grown on a large ■scale, m dull, moist weather, espec■ially m fields exposed to mists, ■heavy dews, &c, about July and ■August, when the foliage is full and ■tinged ; similarly, on heavy wet soils ■unless the season is remark^a^ly ■open and dry, but also, m, ftght dry ■gpDils during rajny seasons. Soevi■geflt was trfis, that many believed ■that the mists and dews brought the ■disease — harking back to the superof earlier years. We must ■remember that it was not till iB6O ■that the life-history of Phytophthora known. Since De Bary's proof the germination of the zoospores of the infection *of the leaves, course of the hyphae m them and the haulms, the origin of the conifee , and the confirmation of th ( c. fungus nature of th£d\seas£, yje now m a posit^o^ to ࿞sfana t>ridcinal factors which cause the epidemics of potato-disease. is not merely that the potato-fields plenty of food for the fungus, that the dull weather causes the to be surcharged with moisowing to diminished transpibut the mist or dew, to say of actual rain, and the flappof the leaves together favour the of the zoospores the field. Whether the dull also favours the accumulate m the tissue ans $$' parof ' the latter implies I^^^Kresisianee to the entering hymay be passed over here, but many cases it is clear that w< several factors of the non-living here, favouring th< and not improving th< of the host, even if they d.( directly disfaypur it.