POWDERY SCAB

Press, Volume LXXII, Issue 21907, 7 October 1936, Page 15

POWDERY SCAB

THE VICTORIAN OUTBREAK

The current issue of the Victorian “Journal of Agriculture,” an exce -nt publication for farmers' use- ana which should provide a standard for the New Zealand Agricultural Department should it ever realise the necessity of improving its journe deals usefully with the outbreak of powdery scab in Victoria. Growers in New Zealand have had very little if any, opportunity of seeing powd ry scab in action, so the article should be informative: — . ... , „ Powdery or corky scab, which has made its appearance in Victoria, ftrsi appears on the young tubers as small pimples or pustules, which may occur as patches or scattered over me surface. As the disease progresses these pustules break through the surface which splits and forms the typical circular cavity with frayed edges, exposing a brown powdery mass of spore balls. Thus the typical powdery scab lesion may be differentiated from that common scab by the more regular contour of the scabs, the ragged margin of broken skin round the scabs, and by the presence of the brown powdery mass. On less typical specimens the symptoms are frequently partly suggestive of- common scab, and in such cases a microscopic examination of the specimen is necessary to distinguish the two diS6BSGS* A cankerous stage of powdery scab disease has been described as occurring in limited areas overseas, in which case the deeper tissue of the tuber becomes infected, and is often invaded by rot-producing organisms, which complete its destruction. This cankerous condition has not been observed in this State.

Powdery Scab is caused by a slimemould parasite Spongospora subterranea. The brown powdery mass consists of many spore balls, each of which contains several spores. When these spores, germinate, they release tiny naked jelly-like bodies, several of which unite to form what is known as a plasmodium. This plasmodium enters the cuticle of the young tuber and feeds on the cell contents. The organism does not proceed to a depth of more than a few cells. Ultimately, by a division of the organism, a new spore mass is produced under the cuticle, and the typical scab formed. Some of the spore balls are detached from the tubers, and may be left in the soil when the crop is lifted, while others are distributed with the tubers. Thus the disease is both seed and soil borne. It is uncertain how long the powdery scab organism is able to live in the soil, but English authorities believe that they have evidence that a new crop may be infected even after a lapse of three to five years. Cool weather conditions and low, wet soil are most favourable for the development of the disease.

JOHNE’S DISEASE

TARANAKI OUTBREAK

PUREBRED HERD DESTROYED

An item in the daily papers the other day mentioned that owing to the evidence of Johne’s disease in a Taranaki dairy herd, 103 pmrebred Jersey cattle had been destroyed. The whole of the herd was removed to Patea and destroyed there as a precaution agamst the spread of the dIfiCQSC For some years past the farm and herd have been under restrictions by the department in an endeavour to eliminate the diseased animals one by one, but the infection of the soil rendered the task a difficult one. The drastic action of destroying the whole herd resulted from a change of ownership of the herd. Compensation has been arranged on the basis of payment by the (iovernment of half the value of the stock at valuation when condemned under the provisions of the Stock Act The maximum valuation allowed by the act is £l2. Incidence of Disease Johne’s disease, first discovered in Denmark in 1895, is caused by a baccilus taken into the intestines from infected pasture soil or from drinking water in swampy ground. The intestines become severely inflamed and “corrugated”; there are intermittent attacks of diarrhoea, which become progressively worse. The animal lose? condition until death occurs. Infected animals show reaction to the Johnm vaccine test There is no known cure, and to obviate spread the animals must be destroyed. . . .. Infection frequently takes a long time to develop symptoms, but over a period of 12 months attacks of diarrhoea and loss of condition are generally regarded as warranting the Johnin test to determine the complaint. Johne’s disease is scheduled under the Stock Act and any cattle found by the department must be condemned. New regulations were gazetted this year, and these provide that no cattle may be shipped from the North Island to the South Island without a permit and the application of the Johnin test. Of the 103 cows in the Hawera herd destroyed, 33 reacted to the Johnin

test. The farm will be closed to cattle for some years, and heavily limed, and stocked with sheep. Sheep were also suscertible to the disease, and none could be taken off the farm except for slaughter. Milk was not affected. Twelve other dairy herds in the Hawera district were known to be affected and the reacting animals were being culled out. The disease has been known in the Waikato, where a number of tests had caused beasts to be slaughtered. The incidence in that district, however, was not very severe. The disease has not been reported In the Manawatu or Wellington dairying districts, nor anywhere in the South Is’and.