SUMMER FOES

New Zealand Herald, Volume LXXIII, Issue 22344, 15 February 1936, Page 8 (Supplement)

SUMMER FOES

FIGHT AGAINST PESTS By far the larger number of queries received from horticulturists are in connection with some pest or disease which is attacking their crops. When the weather is warm and mild, plant foes flourish. Many of them increase at a phenomenal rate, and unless prompt measures are taken at the outset subsequent sprayings will not do the same amount of good. For instance, that common foe, the greenfly, may at first infest a few shoots, where it is readily killed by means of one of the many efficient insecticides. But once allow these, aphides to multiply sufficiently for some of their number to be driven to the older foliage, they immediately protect themselves by curling the foliage round themselves so that it is almost impossible to bring the spray solution in contact with them._ Similarly with many fungoid diseases. once the fungus has grown well into the tissues of the leaf and stem, it is of very little use applying even the most reliable fungicides. The allimportant thing is to cover the foliage with a suitable spray before the damage is done, so that any spores carried on the wind from a neighbouring tree or plant are killed as soon as they attempt to grow. The Appropriate Spray

The selection ot the appropriate spray is the stumbling block with many gardeners, but one does not need to bo a learned plant pathologist to carry out a successful campaign against the commoner pests and diseases met with in an average summer. The number of foes which may attack the crops is certainly numerous, but fortunately they may all be classified under three or four main headings, at least as far as treatment is concerned. First of all it is necessary to distinguish between what are rather loosely termed " pests " and " diseases." By the former term is usually understood some insect or caterpillar which lives on the plants, whereas a "disease if caused by a fungus, or in some cases a virus. The last-named are the most difficult, for although a gooo deal of research is being carried on as to their nature and cure, very little of a positive nature has been recorded. Diseases of fungoid origin do not, however, present the same difficulties, as the spores are readily killed when brought into contact with a sulphur or copper salt. Theso compounds, compounded by skilled chemists, may be purchased already mixed. Ordinary flowers of sulphur hat often been used as a dust for mildews on plants, and while this method has the advantage of simplicity, it cannot bo considered as efficient as some of the modern sulphur preparations for plant diseases. Two of the£e are lime sulphur and colloidal sulphur, the lastnamed being particularly penetrating in action, and now, also, a colloidal copper fungicide is proving effective. With these proprietary fungicides it is necessary to apply them in the form of a fine, driving mist, so that as good a cover of the leaf surface as possi bitis obtained. Two Classes For the purpose of devising measures against pests the most convenient way is to divide them into two classes—those which attack plants by sucking the sap and those which feed by biting the leaves and steiE3. Greenfly, red spider, thrips, and hoppers belong to the former class, while caterpillars, slugworms, weevils and beetles belong to the latter class. The distinction is important as a different line of treatment must be followed for each ciass. Should the novice be in doubt as to the kind of insect attacking the plants, examine the damage closely. If there are pieces eaten right out of the stem or leaves it is evident that a biting insect is at work, but should there be no sign of holes, but a more or less blotchy appearance, or alternatively leaves that are very much cockled and curled, it is fairly certain a sucking insect is at work.

Insects which live by biting are killed by spraying with some poisonous cnemical, and fortunately while these are toxio to insect life, they are not necessarily harmful to human oeings or animals. Sucking insects cannot be dealt with in the same way. as they do not eat the leaves and cannot be poisoned so simply. Two methods of control are open. One is by bringing a solution in contact with their bodies, and the other is by clogging up the breathing pores of tho insect bv means of soap or oil emulsion. With sucking insects it is absolutely essential to bring the solution into contact with the bodies of the invaders, and for this purpose a rather heavy wetting spray is required.