POTASH SHORTAGE

New Zealand Herald, Volume LXXI, Issue 21990, 22 December 1934, Page 12 (Supplement)

POTASH SHORTAGE

DEATH OF PLANTS The signs of over or under supply of nitrogen were dealt with in recent notes, and the signs- of potash starvation are 110 less prominent to the observant grower, who takes the trouble to study his'plants. Leaf scorch in apples and die-back in fruit trees generally arc plain indications of the lack of this essential element. In the former case tho foliage develops normally, but as growth proceeds, it shows brown discolourations, which spread, and may eventually cover the whole leaf surface. The damage is so similar to that caused by some fungi, that is often difficult to convince gardeners that the trouble is of a physiological and not a pathological nature. Die-back in fruit trees is not invariably caused by a potash shortage, for sometimes the young shoots are actually diseased. The outward symptoms are in either case so similar, that even an expert may be deceived, unless a detailed examination is made. Sometimes a whole orchard may be affected with serious results. Growth ceases early and later the young shoots commence to wither. This shrivelling continues after the falling of the leaf —which may bo premature—and by spring it is quite possible that all the wood made the previous season may be dead. Many soils are deficient in potash, and' other soils not actually deficient may have an excess of some other constituent such as phosphates. Both of these types of soil will benefit by applications of potash. The importance of potash in the physiology of plants has long been known, in that it serves as a means of enabling starch to move from one part of the plant to another, for instance from the stein and leaves into the tuber in the case of potatoes. Moreover, the juices of plants which aro noticeably sour, such as lemonjuice, the sap of rhubarb"stalks, and the...juice of sodr apples, gooseberries and grapes, commonly contain an acid salt of potash, which changes to sugar as the fruit becomes ripe. Certain plants are very sensitive to a shortage of potash, for example, peas, beans, apples, pears, raspberry and gooseberry, plum and most other fruits, potatoes and tomatoes. If this very necessarv mineral is lacking the plant will not grow so well and may fall a prey to bacterial or fungal diseases, much more readily than a normal plant. Potash deficiency has been found by experiment to bo a predisposing cause to the following diseases: Apple and pear canker, leaf scorch of fruit trees, bean chocolate spot, potato scab, rose black spot, raspberry, and strawberry diseases and tomato stripe. Other control measures would, of course, be taken where possible, but potash treatment is essential with these diseases. Other crops benefit from potash dressings in relation to their diseases, even if the results arc not so striking. In general, fruit trees need potash most, and vegetables least, but all benefit from tho'application. PEST OF PEARS DAMAGE BY SLUGWORM Much of tho fruitgrowers' work during tho next few weeks will consist of ensuring the well-being of the trees by keeping down insect pests, especially those which damage the foliage and fruit. The slug-like caterpillars of tho sawfly (Eriocampa limacina) feed 011 the upper surface of the leaves of pear, cherry, and quince causing light brown patches to appear. The lower, surface of tho leaves is not eaten. When the damage is severe the leaves wither and fall, in which case the trees are weakened, in all possibility for several years. Tho sawflics are shining black and only about half-an-inch in length. The eggs are laid in somi-eircular slits made by the " saw " of the females in the leaves. Tho caterpillars aro dark green

Poar slufjworm, which defoliates the trees. in colour, fclia head being hidden beneath the fore part of the body. These caterpillars, being covered with a dark, shilling slime, are of a somewhat loathsome appearance. The caterpillars mature about the end of January, just prior to which time they become yellowish in colour and free from slime. Pupation takes place within the soil, in a cocoon. A second generation may be found feeding during February and March and it is this second brood which causes the most severe damage.' ihe winter is passed iri the larval stage in the soil pupation taking place in spring. In the case of single trees the soil may be removed to a depth of four inches and burned. Soot and lime dusted over the leaves are often fairly effec-, tive. Spraying with arsenate of lead is, however, the only method on which reliance caij bo placed.