POTATO CROPS.

Dominion, Volume 1, Issue 70, 16 December 1907, Page 2

POTATO CROPS.

WHAT WILL HAPPEN IF IT RAINS?

SOME REASONS FOR SPRAYING,

RAIN PROBAJ3LEI Though wo havo takon no degree in weather forecasting, wo imagine there is, at tho time of writing, a sufficient- abundanco of "indications ' to justify us in hazarding a guess as to what weather may prevail'during the next few days. ■ Wo havo an abject in thus going out of our way to meddlo in weather. Wo desiro to wnto about potato crops, and to warn tho proud owners of undiseased potato patches that if our forecast bo truo, and rain descends 111 prolonged warm showers upon unsprayod plants, the prido of the owners is in peril of being blasted by ono of the do-' structivo visitations that tho blight likes to pay us in tho course of every season. There havo been blight outbreaks already in somo parts, but wo havo had no typical blight weather yet, and many potato fields, no doubt, have weathered tho season very well. I'ungus blights of all kinds make verv laboured headway in dry weather: Tho spores do not germinate, or, if they do germinate, they perish in the attempt to root into a leaf pore, and foolish potato growers say in their hearts, "There is no blight." True; but thoro are millions of blight spots, still ■waiting for wot weather, and when tho rain falls those spots will awako into a sea of activity to make up for lost time. It does not take many hours for blight spores to,attack a plant beyond cure, nor many days for that attack to become painfully apparent to the disappointed owners. Tho wise men will spray to-day, and spray well. Good spraying, of course, does not' mean simply a heavy drenching, but spraying with Bordeaux mixturo correctly made,: and with a powerful sprayer that emits a mist-like cloud to settle softly, completely, and permanently on the foliage. Bordeaux mixture is a preventive, but not a dure. There is no cure. There is nothing known on earth that can, whilo sparing tho potatoes, destroy tho exasperating brown spots that wo call tho blight, when onco they aro established. We spray to prevent those spots appearing. Wo spray unaffected plants to keep them clean; and also wo spray affected plants to save thorn from furthor infection.' But nobody noed spray to removo tho brown spots already visible—as you would rub an old coat with ammonia to remove grease spots—nor to prevent thoso spots from becoming larger, l'ou spray solely to prevent , additional germs from entering to mako new spots; and incidontally you spray because tho stuff that Bordeaux mixture is made of acts as a tonic to the plants, and does them somo sort ofgood, improving their growth, and' adding avoirdupois to tho tubers. Tho visible and invisible dust that rolls over tho leaves of ovory plant is made up of soil particles, plant particles, pollen grains, seeds, minute .insects and their eggs, tho germs of iniiumerablo organisms, and other matters. In dry weathor the constant movement of these particles nuist necessarily render their lodgment in the leaves difficult. But, rain or dow makes the leaves adhesive, and at tho same time causes an outbreak of sprouting among the hordes of germs. Many of the germs that aro at this moment on a potato leaf aro of a species unsuited to grow on its tissues, and after fooling out vainly for their natural food withit.heir.Tittlo "rootlet" they perish; But ; ainong tho.rest there are, perhaps, half a dozen spores of phytophthora iufestans. Each sends- out its feeler for food. Somo...mysterious .power iitt'racts-i.the/gro'iv-ing poiht"dpinV ;ii}t'o"."a '"pores', it "gets greodijy; r^ldj known agency can stop' its attack—short of cutting olf the leaf tissue itself. But there is another side.to the picture. Tho owner' of that potato patch -has, perhaps, been wise, and has previously sprayed tho leaves,over and under, with - Bordeaux mixture. The sporo sends out its "feeler"- as before; it glides along the damp -surface of tho leaf, absorbing moisture as it goes, and with tho moisture it absorbs copper snlphato — a deadly poison. It promptly perishes,' and the potato plant lives. This is tho theory of spraying for fungi, and it is a theory that practice supports and • that specialists in every country subscribo to. o Twenty letters were published in the Agricultural Department's Report for 1906, on page 354 and following pages, giving clear proofs that Bordeaux mixture saved the potato crops. Tho experiences quoted in those letters repeat themselves every year and in ovory country where potato blight'exists. Ono of tho letters is worth referring to. It was from Mr. Henry Burrell, of Feilding. Ho had thirty acres of potatoes, from which be got a 14-ton crop—worth several thousands of pounds. Ho states that in consequonco of hearing a-lecture of Mr. T. AY. Kirk (Government biologist) on. tho potato blight he cabled to London for a "Strawston" potato-sprayer, costing in London £9 15s. It is an instrument which is fixed to tho back of an ordinary cart, is ■worked by hand, and sprays five rows at a time. Two nozzles, going close to tho ground between the rows, send the spray well on the under sido of tho leaves, and ono .nozzlo on the top sends out a fine spray above, so' that on a. clear, still day '• tho dray appeared to travel across the paddock in a fog." Fivo or six sprayings were given, and two men with a horse and dray prepared tho mixturo and sprayed ten acres a day. The quantity used was 60 gallons per acre at each spraying; and tho cost for tho season was from ss. to-ss. . 9d. per acre. Tho gain was a. 14-ton cropj worth several thousand Douiids. . .