TYPICAL PLANT PESTS and DISEASES

LATE spring and early summer usually sees a rapid build-up of pests in the garden. Aphis, including greenfly and blackfly, breed prolifically with the arrival of warmer weather and one female can quickly produce a colony of these pests which will do much damage unless they are checked. They are usually found on the young shoots of many plants, often in the growing tips where they are not immediately visible, sometimes on the undersides of leaves. These pests may be dealt with in various ways. The plants may be sprayed with an insecticide such as derris or pyrethrum, or one which contains both of these substances. Spraying should be done vigorously so that the liquid is forced into the growing tips and care should be taken to see that the undersides of the leaves are properly wetted. The same insecticides are obtainable in the form of powders which are dusted on with a blower, taking the same precautions to ensure that the growing points are adequately covered.

Roses growing against walls are often attacked by aphis, even more than those bush roses growing in the open. ‘Dorothy Perkins’ is very susceptible. But damage on wall-grown roses is caused not only by the pests but by a fungus disease which follows them and which causes the shoots to look grey and mildewed, the grey eventually giving way to an unsightly black deposit. Here again, it is advisable to spray forcibly with derris or pyrethrum and repeat the operation at fortnightly intervals in case any breeding females have escaped.

Caterpillars of various kinds (the larval stage of moths and butterflies) often put in an appearance in late spring and early summer. They can cause much damage by eating leaves and growing points. Fortunately the derris and pyrethrum sprays are also effective against these pests. Once again, spraying should be done forcibly and the undersides of the leaves should be covered as well as the upper surfaces.

One peculiar pest which is found in almost every garden in spring and summer is the Cuckoo-spit insect, also known as the Common Frog Hopper. The ‘spit’ is a protective froth which the insect exudes. Any gardener who has removed this knows that underneath it is a greenish-yellow insect. This sucks the sap of the plant, causing the shoots and stems to become distorted and to wilt. It is found almost invariably on lavender bushes, but also attacks roses and geums as well as some other plants. It is not the easiest of pests to deal with as the froth which it produces, which is intended to protect it against birds and other enemies, also protects it against garden sprays. However, it is possible to outwit it by spraying really hard with clear water to wash off the protective froth and then dusting the plants with derris or pyrethrum. A forceful spray with a liquid preparation of derris or pyrethrum will also deal with the pest but may be somewhat wasteful of material as it must first be used to wash off the froth.

Too often gardeners forget to regard hedges and ornamental trees as a source of infection by pests and diseases. They spray assiduously their roses, dahlias, chrysanthemums, fruit trees and bushes, but they fail to realize that pests can be lurking in the hedges.

So when you go round the garden, as you should once a week in summer with your sprayer, take a look at the hedges and at any specimen trees or shrubs that may be growing in borders, or perhaps in the middle of the lawn. If there are any signs of pest damage, or if you see any greenfly, blackfly, caterpillars or other pests, spray the hedges and specimen trees as well.

Remember that a greenfly born on Sunday can be a grandmother by Wednesday. Regular spraying, not only of your precious roses or dahlias, but of everything else in the garden is the only insurance against these pests.

In the summer months you may find that the leaves of your roses, lilacs and various other ornamental plants have been eaten away – usually the missing portion is neat and regular. The culprit is almost certain to be a leaf cutting bee. These bees remove part of a leaf and take it to the nest to make cells for their larvae. This kind of damage to the leaves of ornamental plants is not really serious. It is disfiguring but the plants will not suffer very much. Far more serious is caterpillar damage, but here it is usually possible to see the caterpillars at work and then they may be easily destroyed by spraying with a good insecticide.

If you are growing chrysanthemums you may notice a number of white irregular lines on the leaves. These are caused by the chrysanthemum leaf miner Phytomyza atricomis. A bad attack of leaf miner on chrysanthemum or indeed on any other plant can seriously affect growth and should be checked at once by spraying the plants with a BHC spray. It is particularly important to keep leaf miner in check on chrysanthemums that are being grown in pots to bring into the greenhouse in the autumn. Many chrysanthemum growers spray their plants with a BHC spray in one week and with a derris or pyrethrum spray the following week.

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