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No. 36 (September 1961)
– 58 –

BLACK ROT IN KUMARA

Some ten years ago, the Maori people in North Auckland and the Coastal Strip of the Eastern Sector of the North Island produced crops of kumara which not only formed part of their diet but economically constituted a fairly high percentage of their income. The produce was distributed throughout the North Island and on numerous occasions exported to South Island main centres.

Today it could be confidently stated that owing to the ravages of Black Rot, production by the Maori people has declined rapidly. With this in mind it is proposed to emphasise the need by growers to take more care in the selection of seed for propagational purposes and a strong recommendation that rotational cropping be observed, especially where there is any suspicion that the disease may be present.

Black Rot may occur if present in the soil, on any of the underground parts of the plant. On the kumara the disease produces dark to nearly black somewhat sunken, more or less circular spots on the surface.

In the early stages these spots are small and nearly round, but under favourable climatic conditions they enlarge until frequently nearly the whole kumara is involved. Often in the centre of the spots will be seen more or less circular areas, from ¼in to ½in in diameter in which may be found fruiting bodies of the fungus. The surface of the infected spots has a somewhat metallic lustre and the tissue just beneath the infection is usually a greenish colour.

On the plants the infection begins as small black spots which gradually enlarge until the whole of the stem is rotted off and on numerous occasions it extends up the stem to the surface of the soil. This is often noticed during the early stages from two to three weeks after planting has been completed.

It is very important to remember that if Black Rot kumaras are used for seed the plants derived from the parent tuber will in all probability be infected. Another very important point to note is that Black Rot infected kumaras, when cooked, have a very disagreeable taste and a peculiar odour is present when cooking, therefore it is not in the interest of the growers to offer for sale such produce, as the effect on the market is depressing together with the fact that the disease is being transferred from one area to the other.

It is reliably stated that all varieties of kumara are subject to this trouble and methods of control would be similar. The Department of Agriculture have in conjunction with the Department of Scientific Research prepared a very comprehensive leaflet which is available on application to the Department of Agriculture, and it is suggested that any Maori grower who is concerned or suspicious that his crops may be infected should make application to the nearest office of that department, where he will be given every assistance and co-operation by field officers, who are at present keen in their desire to assist if possible to eradicate Black Rot in kumaras.

They suggest that selected tubers should be dipped in 50% Dichlone (Phygon XL) at 11b to 100 gallons of water before storing in clean boxes which have been dipped or thoroughly sprayed with commercial formalin at 1 gallon to 49 gallons of water.

In the case of the Maori pits or store houses which are common in the Tauranga coastal area, the above preparation would still apply. The pits in this case should be thoroughly sprayed before storage takes place. When propagating beds are being prepared for planting all introduced material, including stable manure, straw, hay, soil or sand should be drenched with Phygon XL at 11b to 100 gallons of water.

It is sincerely recommended that all Maori growers who have the opportunity to read the foregoing notes endeavour to exercise the very necessary control measures in the interest of their people who have for many, many years been so successful in producing such an economical crop, which has over the years brought about stability in various remote Maori communal areas.

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The National Art Fellowship, tenable for two years and valued at £500 a year, has been awarded to Mr Raukura Hotere, of Hokianga. He will study basic design in the Central School, London, under the fellowship before returning to New Zealand.

Mr Hotere, who is of the Rarawa tribe, living at Hokianga, with close affiliations to Ngapuhi, is at present engaged as an art specialist by the Department of Education at Auckland. An article on his work will be published next issue.

His entry for the fellowship, one of 15 received, was a series of paintings and drawings.