Pests, diseases and their control

Press, 15 September 1976, Page 15

Pests, diseases and their control

Happily the home gardener has but a few pests and diseases with which to contend and it should l»e borne in mind that even the incidence of those can be minimised to a great extent by correct cultivation and weed control. Healthy plants grown in their right season are un ikely to be affected bv disease. Weed control is very important. Apart from harbouring slugs, snails, cutworms and other pests, weed patches are also a haven for thrip which not only destroy plants but transmit diseases such as spotted wilt on tomatoes. When a pest — or the result of its activities — is spotted, the first step is to diagnose the trouble and then find the best method of treatment. Indiscriminate spraying is useless and should not be undertaken. It should be remembered that insecticides are of little or

no value against fungus diseases nor fungicides of any use against insects. Another very important point which should be emphasised is that many insecticides are poisonous to humans and domestic pets and the manufacturers’ instructions on preparation should be followed exactly. Insect pests are classified under two main divisions — chewing insects and sap-sucking insects. The former chew surface leaves and stems and for them a stomach poison is usually necessary to ensure control. In the second category are those which suck the sap from leaves and stems and for which an insecticide that kills on contact is essential. CHEWING INSECTS This group includes caterpillars, grubs, codlin moth. beetles, grasshoppers, crickets, cutworms, snails and slaters. There are many species of caterpillar but all have a common effect which is the destruction of plants and fruits. The ones

which attack edible plants such as cabbage, are best dealt with by derris dust which is non-poisonous and can be safely applied up to harvest-time. It is necessary to keep all new growth covered with derris dust; Carbaryl 80 is an even better killer but must not be used within 24 hours of harvest. On plants such as beans — which are susceptible to attack from white fly and green vegetable shield bug — it’ is preferable to use maldison, which is also good against leaf miner.

Of the beetle family the brown and bronze are most troublesome. The brown is an adult insect from the grass grub and usually hatches out of the chrysalis stage in November.

It emerges at dusk, alighting on the foliage of many trees and plants but with a special preference for plums, cherries and roses. Carbaryl 80 sprayed early in November is an effective measure.

The bronze, which feeds day and night, may

be similarly dealt with. The codlin moth is one of the worst pests that growers of apples and pears have to control. In spring the codlin moth lays her eggs on the calyx and petal of the flower. These hatch in 8-9 days and find their way into the developing fruit. Later they eat their way out, lower themselves to the ground and so begins another life cycle. Trees should be sprayed at fortnightly intervals from midNovember to midFebruarv with carbaryl 80. Crickets can be a real nuisance. They are voracious feeders and will eat almost any vegetative material. As a change from this diet they are also quite likely to have a go at any clothes left on the washing line overnight. They are attracted by lights and this is what brings them indoors on summer evenings where they will attempt to ease their hunger on curtains or other handy materials. Home mixed killer baits were once the only answer against the cricket but reports of a new commercially made control known simply as cricket bait are highly encouraging and this should be tried. The cut worm is extremely destructive and a couple can cause the loss of a number of plants in one night. Diazanon granules should deal with them as it will with the wire worm.

Snails and slugs are terribly destructive and must be kept in check. Blitzem is the most effective bait known and can be bought in pellet or liquid form.

Just follow the instructions on the packet. For woodlice or slaters, boiling waler is as effective as most things but where they are very prevalent, diazanon granules should be used. SAP-SUCKING INSECTS Included in this category are aphids, mealy bugs, red spider, scale, thrip, green vegetable (or shield) bug and woolly aphis.

Maldison is a good killer of most of the insects in this group but should you find aphids a particular problem then menazon 25W will prove most deadly. An application of menazon on rose bushes and other ornamentals, goes straight into the sap stream where it remains for three to four weeks. PLANT DISEASES These are quite different from insect troubles and come under three general divisions — phys-

iological, virus and fungus. The first-named are brought about by malnutrition and need only an improved food supply.

Virus diseases include bronze wilt (tomatoes) and leaf curl (potatoes) and many somewhat obscure troubles. No discovery has yet been made' which is capable of re-i storing plants to health! once attacked.

Expert identification is | usually necessary and if found, the main pre-1 cautions are to avoid a; repetition of a crop ini the same ground and to. immediately remove from, the bed all affected!

plants. Virus diseases are not) quick spreading and the! pulling out and burning of the affected ones — plus a spraying for aphis: — will check the disease. I Presence of a virus) problem is indicated in several ways: Mottling of foliage showing light and dark green parches; dwarfing and wrinkling of leaves; rolling of leaves which turn into the centre stalk (usually commencing with the lower leaves and working upwards); general dwarfing of the plant with a marked failure to branch out, producing the effect of unnatural uprightness.

FUNGUS DISEASES These are the most predominant of all and are caused by harmful fungi which attack the plant either through the root system or directly on the leaves and stems. Most common are black spot, mildew, downy mildew, late blight, fusarium wilt, root and crown rot. There are others. There are several varieties of black spot, one of which attacks fruit trees. On pears and apples it appears as a small black spot on the foliage, gradually increasing in size if not sprayed. Later it infects the fruit, the spots running together so as to cover the greater portion of it, ultimately causing decay. All forms require similar treatment — spraying during early spring at the commencement of bud movement with Copper oxychloride or bordeaux mixture.

This should be followed by a summer application of captan, fruit tree spray or benlate.

If you are unable to' identify any problem, an accurate description to your local seedsman will probably tell him what it is and he will advise on the best means to remedy the matter.