STRAWBERRY PESTS AND DISEASES

Otago Daily Times, Issue 22824, 7 March 1936, Page 24

STRAWBERRY PESTS AND DISEASES

A few years ago strawberries were in a bad way, and growers in many districts were worried by the signs of ill-health and the poorness of the crops shown by even varieties of good repute. Lately, however, matters have been put on a much better footing, and many of the old strains rejuvenated by good cultivation and a better understanding of the causes of the trouble.

It is, unfortunately, liable to attack by several pests and diseases, but the list of possible troubles is no more formidable than those to which other fruits ar« prone, and risk of any serious menace can be almost entirely obviated by attention to cultural details.

The two fungoid diseases which are most prevalent among strawberries are mildew and leaf spot, but both are easily controlled by sulphur, if it is applied in the early stages of attack. A 3 per cent, lime-sulphur spray will be effective, or the powdered form of flowers of sulphur can be dusted on the plants. Leaf spot confines its attack to the leaves, where it forms round, purplish spots, and does not usually harm the crop, unless it is so widespread as to interfere seriously with the work of the leaves. Mildew can spoil the crop, as it covers the berrie3 with a white powdery deposit, but, as it usually appears first on the foliage, too, damage to the fruit can be prevented if control measures are taken promptly on its appearance.

A yellow or rusty appearance of the leaves, which is sometimes mistakenly thought to be a form of fungus, because the agents causing it are too small to be seen, really denotea the presence of red spider, a tiny mite, which congregates in its thousands on the undersides of the leaves, and sucks the sap from them. Warm, dry weather is most favourable to an infestation, and moisture alone is a means of control, while other effective measures are the application of sulphur compounds, as for mildew. A more serious menace is an even smaller mite, the Tarsonemid mite, which is so minute, being only l-120th of an inch long, that its presence is often unnoticed until it has increased to large numbers, and then only by the resulting qnect on the plants. Strawberry plants which are infested have small, weak and deformed leaves, and in severe cases the crown dries up, and does not develop at til. The mites dislike daylight, and collect in the young unopened leaves round the growing point of the plant, puncturing the tissues to extract the sap. This pest has only been discovered during the last few years, and the best control method known is again lime-sulphur. It will be evident from what has been eaid of the habits of the mites that to be effective the spray must be directed with considerable force into the heart of each plant. This wash is fatal to the mites themselves, but does not kill the eggs, and so more than one application may be necessary during the egg-laying period in order to kill mites which have hatched cut in the meantime. Egga are not usually found on the plants during' the winter, but are laid from September to March. As lime-sulphur may cause scorching of Iho leaves during strong sunlight, a dull day, though not a wet one. should be chosen for the spraying operations. Another pest which may be present all the year round on the plants i« the strawberry aphis, which is one of the causes of "small leaf." The best time"to take measures against it is in November, when the aphides are feeding on the young leaves, und can be killed by spraying with a nicotine and soft soap solution. As this wash will probably be needed for greenfly on roses now, it will entail very little extra trouble or expense to use it on the strawberry bed at the same time.

These are the most common troubles and diseases, although it is not an exhaustive list of all tlie possible ones. It is significant that one trouble may lead to another, either directly through the aphides or mites acting as earners, or indirectly by lowering the vitality of the pla-nts, and so predisposing them to fall victims to the next foe; but it is possible that they may all be avoided by taking certain measures which will lessen the risk of any attack. The first of these precautions is to propagate only from clean stock, obtaining the young plants from a good firm, if they are bought, or choosing runners from perfectly healthy plants in one's own garden. A further safeguard against aphides is to dip the tops of the young strawberries in a nicotine and soft soap solution before planting them. These dipped runners should be then planted out without delay. The second consideration is to cultivate the plants so well that they are constitutionally strong and healthy, and better able to resist any onslaught by pest or disease. This involves, beside the routine work of hoeing, strawing, etc., a thorough preparation of the ground before making a strawberry bed by deep digging and manuring, as well as feeding the plants iu after years by means of a lnanurial mulch or artificial fertilisers.

A third wise plan would bo to net on the principle that " prevention is better than cure," and to maintain a regular routine of spraying or dusting, even if the plants appear lo be in good health, fn autumn all decaying leaves should be removed, as well as those which show signs of disease, such as leaf spot; any unhealthy-looking plants should be rogued out, and the bed dusted over with flowers of sulphur. In September a lime-sulphur spray, at 3 per cent, strength, will account for mites before the egg-laying period begins, and will ensure that the voune growth of the plants gets a good start in development, while a nicotine wash in November will check attack by aphis. This is not an elaborate programme, and will probably be sufficient to keep the plants in a healthy state, though it can be extended to meet any particular trouble which becomes noticeable.

To keep the beds clean is part of the routine work which should be done as a matter of course. Hoeing and maintaining clean cultivation, not only in the strawberry bed, but in the adjacent parts of the garden, will lessen the number of slugs and snails, though a few slugs are almost inevitable in wet weather; while the timely adjustment of netting will frustrate the birds' efforts at obtaining first peck at the fruit. Occasionally rats and mice, and even toads and frogs, have been known to show a partiality for ripe

strawberries, but if the herring netting which covers the bed is attached to a surround of small-meshed wire netting, the amphibians will be baffled, and if the rodents burrow under it, their runs will be easily seen, so that traps can be set for them.

There is also a beetle that has developed a taste for strawberries, but it is not very common, or, otherwise, the. damage it does is laid to the charge of the slugs and snails, for it eats similar holes in the fruits. Trap this with sweetened water, as for ants and other like epicurean pests. Old large plants of strawberry should not be tolerated; they offer fine harbourage for pests «s above, and should be grubbed up and burnt after their third season. A young plantation should always be following, and to this end propagation by layering should be an annual occurrence. Plant a new bed every year, and destroy the oldest one. If this plan is adopted, finer fruit will be grown, and cleaner, healthier plants will result.—V. E. W., in Amateur Gardening.