FUNGOID DISEASES

New Zealand Herald, Volume LXXI, Issue 21792, 5 May 1934, Page 8 (Supplement)

FUNGOID DISEASES

INFLUENCE OF WEATHER Tho favourable cffoet of wet weather on fungoid diseases is familiar to all gardeners, but the explanation is seldom understood. Fungi, like other plants, need moisture and cannot survive dry conditions, except in tho resting state. To onablo fungi to multiply, tho weather must : be favourable not only to spore formation, but also to spore germination,, and to, the penetration of tho plant tissues by tho young fungus. Considering first sporo formation, the prime essential hero is a moist atmosphere, i.e. high humidity. Potato blight will not form spores if tho relative humidity is below 75 per cent and 75 to 80 per cent is tho minimum for nearly all fungi. On a dry day, when the humidity is usually 60 per cent or less, fungi can make no progress. On a wet, rainy day the humidity is 00 to 100 per cent, and in the " muggy " weather sometimes experienced in summer the humidity is also high. Both typos of weathor are favourable to blight and other diseases. EFFECT OF TEMPERATURE Besides high humidity a suitable temperature is essential to the growth of these diseases. If it is too cold! as is usually the caso in winter, the disease fungi can make no progress. High humidities are often experienced in spring and early summer, nut until the air temperature ceases to fall at night appreciably below 50 degrees Fahrenheit, there is no danger of potato blight beginning. This explains why diseases start earlier in tho milder northern portions of Now Zealand, than in the south. In greenhouses as a rule, higher temperatures prevail, and it is possible for potato blight to be developed there in tho depth of "winter. Diseases of greenhouse crops have their own temperature relations. Tomato mould will not develop until tho temperature exceeds 64 degrees Fahrenheit, for an appreciable time, and increases most rapidly between 70 and 80 degrees. Potato blight makes rapid progress in warm weather, but is checked by hot weather. In the greenhouse, raising the temperature to 80 degrees Fahrenheit, and keeping it there will euro plants of tomato sleepy disease as the fungus thrives best at cooler temperatures. Powdery Scab and wart disease of potatoes flourish in cool soil temperatures, but tend to disappear in hotter climates. Onion Smut behaves in a similar manner. Turning to spore germination, for this not only moisture is essential, but there must be a film of water (dew) on the leaf surface. For diseases like potato blight, mildew of peas, and peans, dew is the most favourable, but it is not sufficient for apple scab. The former disease will then be favoured by cool dewy nights, while apple scab requires wet rainy weather. Pain is also essential to the dispersal of the spores of apple scab. PROORESS OF DISEASES Once a disease is established in a plant it can grow through it, more or less independent of the weather, as the fungus obtains its moisture from the living tissues. The spread of the disease from plant to plant is however, dependent on tho weather: i.e. the progress of a disease is governed by the weather experienced. This is a familiar fact in the case of potato blight which spreads rapidly during humid weather in January. A wet November means severe apple and pear 1 scab; and epidemics of blossom wilt. If it is warm and humid in November and December, roso mildew, gooseberry .mildew and tomato mould will' be severe. Black currant leaf spot is favoured by a wet February, while wet misty weather in Septembers favours 'tulip fire and j Narcissus leaf scorch. It is possible to j forecast epidemics from a study of tho ' weather; tho problem is complex, but j it has been satisfactorily solved for j grape downy mildew, potato blight and j apple scab. The conditions which lead j one to expect a blight epidemic may be given as an example. They are a i minimum air temperature of 50 degrees { Fahrenheit, relative humidity not less I than 75 per cent for two days or more I and dew at night. When theso are ex- j perienced, blight may be expected with- j m 14 flays, and spraying should be done ! at once. LIQUID MANURE TESTS ATTRACTION TO PESTS A correspondent relates his .experience, with liquid manure, over two seasons. Two beds of dwarf dahlias were planted which are termed A and B. Those in bed A wero fed with liquid cow and sheep manure, and wero badly attacked by the usual pests (caterpillar etc.); while thoso in bod B were not fed at all, and were quite free from pests. Now is it possible that the use of theso liquids gave off a slight odour, and so enticed egg laying flies and moths? Tho dahlia hods wore 6ft. apart. Among other plants the same effect was observed, that thoso in receipt of liquid manure, wero more infested with pests than those not so treated. The " led" plants of course, gave the best results as to size of blooms and vigour generally. Tho use of cow or sheep manure in liquid or solid form would not encourage plant pests, except thoso which habitually breed in such manures. The explanation is no doubt, that the " fed " plants were more succulent in growth, ami therefore niorc palatable to the posts. Conversely the " unfed " plants made growth of a more woody nature, not so inclined to invite attacks.

TO CORRESPONDENTS " Curious'" (Miitnkima). The banana passion fruit docs not Vequire another pollinator. Possibly your plants are too young and will give better results next season. See answer to " Inquirer." T\B.A. (Te Katiwhata).—The caterpillar specimens aro those of the white butterfly. The pupa on the leaf is from the cabbage mofli. Spray with two tablespoonfuls of salt to one gallon of water. " Inquirer'' (Onewheroi.—'The passion fruit is probably too young to set fruit and will Rive better results next seuson. Manure next spring with three parts super to ono part aulphuto of potash " Pas" (Morrinsville).—There is no way of keeping the paspahun out of the lawn except by diggina it out and preventing any paspalum from seeding in tho vicinity. It is often introduced by soil used for topdressing. 11.V.L. (Parakakau), —Colensoa ph.vsalioides is a native plant. Tls known habitat is the Hen and Chickens Islands. The seeds may have been curried by birds or other agency to the mainland. The species is not plentiful and it makes good rock garden plant. K.K.It (Kuwait,.—The specimen is juearandu. It is hurdl.v possible that self-sown seedlings will be found. The seed pods aro light, brown ntiu much the shape and size as an oyster. On open inn: they are found to be filled with thin papery seeds, which soon gerininato in a temperature of (SO degrees. Cuttings aro not reliable Novice" (Dargaville).—l. Sulphur Queen. 2. A. E. Tyson. 3. Mrs R. C. Pilling. •1. Louisa Pockett. 5. T. 11. Jackson. 0. Kara Dow. 7. lima Ratten. 8. Florence. 9. Lord Hopetoun. 10. Pink Boohmor. 11. Ludy Stanley, 12, Hon. W. If. Edgar. 13. Lady Strad broke. M. Mrs. Roger Thompson. 35. Phyllis Cooper. 10. Yellow Mensa. 17. Guy Pngot is. Mensa. 19. Mrs. W. Dnckliam. A.CI.M. (Whakatane),—l. American Golden Russett. 2. Cox's Orange Pippin. li. Scarlet Nonpariel. 4. Gnscoignc'e Scarlet. 5. Tho spots on tho npple are caused by bitter pit. Prevention consists of ensuring satisfactory drainage and avoidance of severe pruning. Manuring with potash will also improve the health of tho tree. 0. The blight, on the gum is the gum-tree scale. It would be best to destroy tho troo before the scale spreads to tho other trees 7. Tho sooty blight of lemons is a secondary efTect of scale infesting the trees. Spray the trees with summer nil'' 4 ,>Ol - . ccnt '- strength d"ring winter, f*. Ihe condition known ns " guminosis" is hard to cure. The disease will occur through over luxuriance of growth or very severo pruning of the top. Reduction of the root eystem by voot-prnning will often alleviate the condition.