Potato Blight

Horowhenua Chronicle, 25 November 1915, Page 3

Potato Blight

THE WOKST bCOUIIGE W ALL. Containing tho.r instructive series ol papers on late blight (or Irish blight) of the potato, the experts or tho N.S. S\. Department of Agriculture .say that the conidia (the roprotlaictive agency of the disease) spread blight in two ways —by attacking the leavor, of healthy plants in the crop and by infecting the tubers. The conidia are Jittle balls that contain a number of spores or seeds. When one of those balls alights on a healthy leaf, tho contents escape from tho case ov enclose wall, and each spore i»egins to push out a tube that may cute! , the leaf either through the breathing pores (stoma taj or through tho epidermis itself. Many conidia fall or are washed lroai the leaves of the plant on to tliu ground, and these the tubers iti the soil amJi Infected tubers little or m> change, there are da/i areas on the eurfaoT. and these become sunken and erumpkxl, and are easily stripped off the peel. If the skin is removed, brown p.itche; or streaks ari to be found just beneath, which extend inwards as the disease advances, and finally the potato shrivels and dius. This condition (sometimes known «.■> brown rust) is the true result ol late blight. The foul-smelling, soft, rotting mass that growers associate with the disease is really the result oi the attack of bacteria that lollow in tho wake of the icail fungus u late blight and set up putrefaction. The soft, rotten condition is us.ui because potatoes are very often dug just after an attack oi late bliglir, and while the weather is still damp. Without being cleaned or dried, they are bagged, and so remain for days — the disease-free tubers the while exposed to every risk of infection, and the diseased ones subject to the nioui favourable condition for the spread ol the attack. The methods to be adopted for tne control of this disease are lo.ir in number. The fiifit is the use of blight-ir<.c-fceedi.' As the nncelium may be dormant in the tuber, though !K)e is "i> outward sign of ih. preset'v. m> ,>ei-0 isJiould be used fnuii a crop that 's known '.■-.. have been tiisoased. fcleeu should bo obtained from a place kno-.vn to have been free from blight for some yt'irs. Any seed showing traces oi brouu rust should be piciced out and destroyed/by boiling or burning. Oiten the grower selects his own seoa after having sent the best tubers oi his crop to market, but it is not goo i policy. It would pay him to keep Mk best for his own mowing, riinieuiberiiu, that "the best h never too good." Land that has grown" potatoes thai have been attacked by blight should ho carefully cleaned, anil, it possible, devoted to some crop of an entirely differ- ' out character lor a reason u: ttvo. There is not a potato district in Australia where this advice cannot be ad- " opted with profit, Tor even if the alternative crop makes a .smaller return per acre, the loss occasioned to ' potatoes grown in soii already confca- ' niinated with mycelium or spores oi ' this disease is likely to ue very Jiea.y l ii the weather i'avoius ;mi oiitbivaJi. ; Parts of the plant anci binall or rot ' ten iiotatoes Jeft in the ground are Ui< * sources or danger, aim every grower should regard it as imperative thao .m ' remains .shoulil bo careluliy collvcti.-ci l and burnt alter liie crop lias been ioJliuved. The practice, ploiiguing <n L potato haulms is likely to piodun: L .greater loss, througu disease, than arij, l incroatie in yield iroin the lnaiuiriai l ' value. Nor aliould the danger oi in- l ( foction being carried lroui one padtij :k u to another by means oi tiw inplements c ' bn disregarded. ' There is nou abundant pi oof thai ;| bpra-ying has jnoved, an almost coin- l pletc remedy against late blight, liiu l it does not do to wait until plants snow a signs oi disease. Spiaying siioukl co- , . * uieuce early, autl every care should be ' s taken ty spray both the lower and up- t per burtaces of the leaves thoroughly; e a-s well as the steins and the .soil, n has been proved that spraying the fci>n prevents tuber infection by the spores that are washed down through the sun. ° The operation nnist bo repeated often ° enough to keep the uiioie plant covoi- ° Cα with the fungicide, and to protect newly-formed foliage- it should no*, be looked upon as a cure lor I. lig:ii, ° for once a plant.is attacKed its case ia li hopekw, and it should be bug out air- fl burned. Several sprayings should us J ' given in and .March to pic- t tect the plants from infection induced fc by the active growtn of blight owing ° t<) the summer rains. Either Jiordeaux mixture (containing 01 b. of cop ° per sulphate, lib, of quicklime, iu 10 '' of water) oi' Burgundy nr.;:- *"' ture (containing Bib of copper sulphate, 1; ipib. i't'-iTusiuig soda, in 40 gallons of '' „. iater) is rccoiu mended. In experi- a luents conducted 'in li-eJand tho Bur- " gundy iniß given the better results. 5 In countries whore tL-.e disease lias c * - existed for many years it has been found 6 that some varieties are much less subject to. w attack than others, and it should always bo the ain: of tho grower if possible, a. disease-resist- T ing strain. It has to be remembered " however, that, a variety that is resist- r ant is one place may not prove so in different conditions. A new variety n # called Era has been grown for l several years in New Zealand, and has a , Ko far yielded excellent results, both F as to blight resistance and yield. . This " variety was raised, from a single plain fe, that remaiued unaffected in a field thai r ' was entirely devastated by blight. .Much a work of a similar nature is being done s ii New South Wales -with our mo_st_ " I'esistaut varieties, .such as Queen of the " * Valley; and though .so far no variety v _ rhas been produced that is totally immime, growers know that- there are <J varieties that are very subject to at-

tackj and that must, therefore, bo avoided-or planted with caution. Much - can undoubtedly be done in this tlirec , -

tion by growers themselves. 1 Regarding the beat time for digping experiments have proved that there is least loss of liggirig is de.ayed • a week or more after the death of 1 lie tops, except in very wet weather a• <I on low heavy soils, in which cases early . digging hecoines essential. •