BLACK-SPOT

Wairarapa Times-Age, 27 November 1940, Page 9

BLACK-SPOT

j HOW TO COMBAT IT. Black-spot makes its first appearance on the leaves about the first week in November, but it came earlier this year. It is not usually observed at blossom time, because the spots are small, scattered, and situated chiefly on the under-surface of the leaf. Their occurrence in this position is due to the fact that the under-surface is first exposed as the leaf emerges from the bud. They may increase later in numbers, until the whole leaf-surface is covered. Infected leaves frequently become incurved or distorted, generally remain smaller, and usually fall prematurely, so that in a season when black-spot is prevalent the trees may lose all their leaves. Fruit infestion usually occurs at the calyx (open) end, as this is the area most exposed to moisture and the wind-borne spores. As the fruit develops, the spots become depressed or sunken. In some cases the diseased area cracks badly. This is the worst apple disease with which the orchardist has to contend. It may be controlled by spraying, but this should be supplemented by the ploughing in of the fallen leaves in winter, so as to reduce the possibility of the spores being carried to the young leaves and fruit. The spraying programme includes Bordeaux at “greentip” stage (lib to 6 gallons), lime-sulphur (1 in 120) just before “pink’ ’stage, and limesulphur (at 1 in 120) every month from petal-fall onwards. Fortunately these sprays-will check almost every other fungal pest, too.

ROOT APHIS HOW TO COMBAT THE TROUBLE. Both carrots and lettuce are prone to attacks of aphis on the part of the plant beneath the soil surface. Young lettuce reveals the presence of this aphis by wilting, even when not dry. The wilting leaves lose their gloss and the plant looks sick and unhappy. Carrot leaves turn yellow, or a’ dull green, and growth stops. Permanganate of potash has proved useful as a deterrent to root aphis which cannot be reached by the ordinary insecticide sprays. On quite young carrots, lettuce, or turnips a solution can be used of one eighth ounce of the crystals to one gallon of water and. for older and stronger plants, the strength can be increased to quarter ounce per gallon without injury to the growth, but with great effect upon the pests.

The crystals should be dissolved 12 hours before use, for although the water is coloured instantly, it takes seme time for all the crystals to dissolve. A sufficient quantity of the solution should be used to soak well down to the roots. When pulling up infested plants, especially lettuce, pour in a little kerosene into the hole thus made and effectively burn or bury the root stump involved. Don’t merely throw it away.