DEEP PLANTING OF POTATOES.

Press, Volume LIV, Issue 16267, 18 July 1918, Page 3

DEEP PLANTING OF POTATOES.

10 THE EDITOR OF "TUB FBESS." Sir,—l would like to reply 'to a number 01 articles occurring m both "The i'ress" and "Weekly j.ioss," 111 which 1 ain credited witu discovering the iucc taat deep-planting is a preventive against >-uo ravages or potato blignt. I'list, 1 wouxu inic to say uiat 1 claimed no such discovery, lor 1 am wen aware thai tnis is a a act of long standing. What really took piace was this. in a recent report/ to cue IWlucation Hoard, 1 drew attention to the iact that many children and teachers nad this year discovered tnat lew, if any, tubers at a uepon ol six mciies or 11101 e showed signs of being anected with blight. 'mis to them was a real discovery, and i mentioned it as evidencing that useful information was being gained at first hand by the children or our schools^ Now that the subject has been ventilated, it is, perhaps, advisable to add a brief note. Deep planting doo3 reduce the ravages of ulight in the tubers themselves, but for obvious reasons deeper planting undor field conditions is not advisable, even if possible. However, if the rows are spaced well apart (28in to 30in) it should be possible to mould up deoper than is practised by many farmers of this district, ■ and the same end can be achieved. But deep planting is neither a remedy nor a preventive against the tops being damaged. -or ruined by blight. 'iho only wise procedure is to spray the leaves with Bordeaux Mixture (4-4-40 strength) about Christmas, and'if the weather be damp, again at intervals of a fortnight and three w.eeks. If every leaf could in practice bo coated with spray, the crop would be quite immune from blight, but as this is hardly possible, it is only possible to claim that the blight will affect the crop in inverse proportion to the care taken in spraying. Small users can buy small tins of Bordeaux Paste ready to dissolve in water. At a symposium of Canterbury Potato Growers, held at Willowbridgo, in 1913, -which it was my privilege to address, it was the unanimous opinion of the forty odd growers present that the worst results to be feared if the crops are sprayed and well moulded up is.at most a loss of 30 per cent, while most agreed that in the absence of blight, spraying resulted in an increase of two to five tons in the crop, due to a thickening of the outer skin of the leaf, with a consequent lengthening of the growing' period. Personally, Ido not think that the tubers are ever j atfected by spores falling on the ground, unless in the case of damaged potatoes, or potatoes completely exposed to the air. Twice 1 have attempted to infect tubers by dusting spores on soil just covering the tubers and lying loose, and also directly on the tubers, and no infection resulted in eiher case. I imagine that tubers are usually affected as a result of the myceium of the fungus, following the course of the digested sap as' it travels from the leaves, but this' view is still disputed. I propose to arrange for more extensive tests during the coming season. 1 suppose I need not remind your readers that the "blight" consists of multitudes, of tiny parasitic plants (fungi) that live on the potato plant, and secure their nourishment at its expense, and that the rapid spread of the Wight in damp weather is due to the enormous rate at which these plants produce spores which germinate on the moist leaves of other -plants. When a crop is badly affected, it is a customary, and, probably, wise procedure, to cut the tops off, and thereby prevent the blight travelling down the stems into the tubers. Thanking you for permitting the use of so much of your valuable space to disouss a matter of some moment.-—Yours, etc., WM. MARTIN, Director Agricultural Instruction. Lower Riccarton, July 16th.