POTATO DISEASES.

Northland Age, Volume 2, Issue 50, 17 July 1906, Page 4

POTATO DISEASES.

(Continued from another page). When the swarm-spores germinate they round themselves off, and then become surrounded with a cell-wall or coat which grows out as a germ-tube, and pieces the epidermis of the host-plant. Having entered the host a new mycelium is rapidly developed, which ramifies through the leaves and brings about disorganisation and decay. METHODS OF SPREAD. From the above it will be seen that this disease spreads on to healthy plants during the summer only by means of the spores, which are blown about in immense numbers from affected plants, and can within an almost incredibly short space of time infect very large areas. A single affected tuber planted in a crop, can serve as an infection centre for a whole district, so that it can easily be seen what danger attends the planting of diseased sets. Healthy tubers may be infected in two ways — Firstly, by the continued growth of the mycelium down the haulms until it reaches the tubers. Secondly, by spores (conidia) being washed by rain and other agencies directly on the surface of the tubers, whore they germinate, and soon set up disorganisation and decay. It is probable that both methods are equally destructive; the latter being especially dangerous in those crops which have not been moulded up sufficiently, and m which the tubers are often within an inch or so of the surface.

This potato-disease is almost wholly propagated and carried on from season to season in the sets themselves, so that the importance of clean seed cannot be too strongly insisted upon. The disease may also hibernate in refuse from a potato-field, and such material may serve as a source of infection during the coming season. It is especially important to remember that this disease can live in warm districts during the winter on tomatoes and petunias, besides other plants belonging to the natural order, Solanacese, of which the potato is a member. Hence an apparently harmless garden-flower like the petunia could be directly responsible for the spread of this disease. DISEASE ATTACKS TOMATOES. When first this disease broke out among the potato-crops in Auckland, special attention was called to the fact that tomatoes were very susceptible to infection, and it was urged that all such crops should be at once sprayed. This advice was, however, by no means generally adopted, and the result was that in Valley, and elsewhere, heavy losses were sustained amongst tomatoes, which, if timely preventive measures had been taken, could without doubt have been saved. The fruit was especially badly attacked, and in many cases a very large proportion of the crop was destroyed. The appearance of diseased fruit is highly characteristic. It first appears in patches which become mottled with brown hard areas. Afterwards the fruit rapidly rots, and, falling on the ground, serves to infect healty plants. Immense quantities of spores are produced on the fruit itself, and the least breath of wind scatters them far and wide.

All tomato-crops should be sprayed at least twice with Bordeaux mixture. This will greatly lesson the danger of infection by Irish blight, and will also ward off the attacks of other tomato-diseases, such as blackspot ( Macroßporium tomato), rust (Cladosporum fulvum), etc. (To bt concluded in our next issue).