THE POTATO DISEASE.

Timaru Herald, Volume LXXXI, Issue 12635, 23 March 1905, Page 3

THE POTATO DISEASE.

A FARMER'S ENQUIRIESCAUSE AND PREVENTION. Somfe time ego-we .received the following letter addressed to. the editor: — Sir,-4t write to J askvif you would give me particulars of the potato disease in your district, as>T notice by tilie papeis it is' very bad in.:'Timaru: -. I will just ask you some questions and will take it as a. great favour'iif 'you will answer them, to thej bast of your', ability, as I am very much-interested. >"-*':"'. .'■ What is the Cause -of the Can it be! rpieyented in way? Are : any crops Pesca-ping? Are they on old land?; Do yW'think taking tpo_ many crops the same'-land .has anything to do -with, it ?■ Do xyou think virgin sail less subject "to. the' disease than old soil? D6"'ypu think land limed less subject to the, disease? =: ' ': !: How do" you think the disease spreads from pneplace to another? Do you think cold weather will stop, its, spread? Do you think a wet or a' dry season causes the disease to spread most? , If there are any" crops escaping, would you describe their -surroundings? . Are isolated crops escaping? ' I am, .etc.. , ■': WILLIAM MUNRO. South Invercargill./^

In order to obtain;: reliable answers to these questions, we sent Mr Munro's letter, to Mr."Kirk,. the/Government Biologist, who has us with_ the replies he "has sent ltf>. tlie writer, in order that they may be published for the benefit of pqtato-growers generally. The following are the answers :'■£-."■ (l)Whafis the cause of the disease? Can ifc-be prevented; in any way? (a); The direct- cause of the Irish potato disease is a specific fungus known as phytophthra. infestans which belongs to that class of fungi known aii the phycomycetes or algal-fungi, so called on agcount of their apparent relationship to certain algae. (b) The- following arc'the chief points to be noticed in preventing this disease. (1) Certain varieties . of potatoes are not affected as much as others; hence careful endeavour should! bs • rnade to determine which varieties are least subject to. the disease, and these only- should be cultivated. Certain • varieties which are apparently highly resistant; in particular districts have in other ojisfricts become extremely Jbadlv diseased, therefore it is almost impossible to recommend any particular kind. (2) All diseased haulms 'should be carefullv burnt and all affected tubers should be likewise -.cremated.,). ;I1 diseased tubers are used for. food'special; care should be taken to burn all peelings,' etc-, and never throw them on the manure or rubbish heap. This is an. extreriiely fruitful source of spreading the disease:-' (3) Avoid using for seed apparently sound tubers from badly affected crops, for it -is these that the mycelim of the fungus h'ibernate.s and- the next summer it emerges-and spreads; destruction far and wide. Great cafe sshould- always be exercised in sowing seed .and anv showing the least sign of disease .should be at once reiected. .' It is hijrhly/ advisable to dip all seed, potatoes before storing them, in Bordeaux mixture; 6-440 formula. This will kill all the spores .on the.surfare "and render them less liable to infection in the. store. .-'..-.• "(4) Plant the rows so far apart that you can earth "them up high. This greatly diminishes the attack!: on the' tubers bv preventing the spores being washed, or otherwise carried "-down on to them, and also mike* it' much more difficult for Ihe mycelim cf the fungus, io grrow down the -stem and thence into/the tubers. (5) In', diseased fields the 'lnni'ms should always be cut and buret before digging is commenced. .This '■■''greatly lessens the risk of fresh infection on the tubers. (6) Do not use highly nitrogenous manures, for crops grown with excess of these become extremely liable-to virulent attacks. Kairiit, potash "salts,;-'and phosphates are recommended as artificial potato manures in affected districts, as these, seem to retard the effects of the disease. (7) This fungus is especially dependent for its spread on moisture. Hence good drainage arid the "addition, of substances which will diminish the moisture of damp soils are useful. Potatoes should not be grown :in paddocks, which are much shaded with trees, etc. (8) The most important means of prevention is careful and systematic spraying with I Bordeaux mixture using the Hme and copper I sulphate Bordeaux, or when quicklime is not

available, the washing soda and copper sulphate Bordeaux. The potatoes should be sprayed beforemoulding up, and again when about half grown. Repeat if necessary. These sprayings should never be neglected even in seasons when the disease is apparently absent, for it has been proved time and again that spraying not only prevents disease but also greatly increases the yield. 2nd Question.— Are any crops escaping, etc. , Isolated crops have of course escaped, the reason being, that, the ,spores of the fungus have not been blown on to them, and-thus infected them. It is advisable to plant potatoes on land which has not been cropped for some years. The use oS lime in the soil especially in ; wet localities would be ■ distinctly beneficial. Third Question: How does the disease spread from place to place? In several ways—(l) by .means of infected tubers, (2) by means of wind and moisture. . The winds blow the spores on to healthy crops, and they germinate whenever there is any moisture such as dew, etc. Human beings carry the spores on their clothes. I have also found them attached to insects.;'. - . - ..

; ■ Fourth Question: Will cold weather stop the spread? No; cold weather will lessen its attacks, but in New Zealand it is never cold enough! to have any great effect. A'wet season is more suitable for its spread than a dry one. In fact in a very dry season the disease would not spreads to .any alarming extent. -,'■' ' -

Fifth Juestion: Are there any erops escaping? *. ■' ■; Isolated crops are escaping. This'is due more to good luck than .anything else. Crops which have bsen sprayed before the disease'appeared have escaped in many parts of the colony. When giving a demonstration of potato spraying in the Hutt Valley in the middle of February, I specially warned growers that unless they sprayed their tomato crops the disease would attack them. Many, however, did not act on the advice. Unfortunately the result has been as I predicted.

A bulletin giving full directions for coping with this disease will be issued by this division before next planting time, and will be distributed free of charge to anyone interested. '