Treating Pests and Diseases in the Flower Garden

Controls and Treatments

The gardener who is interested in herbaceous flowering plants is the one with the fewest problems of pest and disease control and treatment of various other plant ailments. There will certainly be some troubles but in a general way; greenfly, blackfly and caterpillars will always be found where there is plant life but, unlike vegetables and fruit, there are not a great many specific to certain plants. Leafminer on chrysanthemum and cineraria, rust on hollyhocks and antirrhinums, wilt on asters and pansies, earwigs on dahlias and some others are the exceptions that prove the rule.

You may find all through the season apparently mysterious brown spots and brown edges on leaves, holes and tattering on leaves and petals, stems broken and small plants laid completely flat. Most of this can be put down to the weather; wind, hail, sunscorch, frost, heavy rain and salt spray are all sources of damage, about which little can be done, and they are just the luck of the game. Well-grown, healthy plants, staked, fed and watered, will take such trials in their stride, reviving or producing newer growth in no time.

A lack of one or more mineral nutrients in a plant will declare itself in the form of various discolorations on the leaves, stunting of plants and poor flowering. Such deficiency symptoms are not easily diagnosed accurately without professional help; they can be confused with symptoms of virus diseases, or with natural variegations in colour, yellow or cream in most cases, but consistently bad growth and flowering of plants on a particular piece of ground is a good guide. If manuring and feeding do not improve matters after a year or two, then ask for specialist advice. However, real deficiency troubles are rare in gardens; you are much more likely to be contending with pests and blight.

powder from a puffer pack to conveniently apply pesticideVirus diseases are a real but simple problem, once diagnosed; there is no cure, and infected plants should be destroyed as soon as possible before other plants are contaminated. Viruses consist of particles so small that they can only be seen with an electron microscope; these particles are present in the plant’s sap and are absorbed by sucking insect pests (greenfly, capsids, etc.) as they feed. By then feeding on healthy plants, the insects spread the virus and another plant is doomed. Irregular yellow patches, circles and lines on leaves, twisted growth, streaking or alteration of flower colour, and slowly lengthening, stunted shoots are indicators of viral infection but, like deficiency symptoms, are best confirmed by those trained to do so.

Insect and other pests attack in one of two ways: either by biting or by sucking. Caterpillars, maggots, slugs and snails all come into the former category, being armed with, if not actual teeth, mouthparts which can tear or rasp off relatively large pieces of leaf, flower or stem. They are sufficiently sizable to be hand-picked when seen; in really bad epidemics caterpillars and maggots can be sprayed with dcrris or fenitrothion. Slugs and snails should have slug-bait containing methiocarb put down; they feed at night and need to be hunted with a torch for hand-picking.

The sucking insect pests such as aphids (greenfly, black-fly, root aphids, mealy aphid), capsids, thrips, leaf suckers and hoppers, whitefly, mealy bug, scale and red spider mite all pierce the plant tissue with needle-like mouthparts and draw up the sap through them. It therefore follows that insecticide sprayed on to the plant will be very effective and if absorbed into the plant’s sap, even more so; such an insecticide is called systemic. This type of pest breeds extremely quickly and a plague will build up in a few weeks; although squashing with finger and thumb will help, other controls will generally be needed. Root aphids feed in the same way but below ground. Infested plants grow slowly, have a dull colour and wilt for no apparent reason. Derris and malathion are good general insecticides; bioresmethrin is good for aphids, whitefly (for which it was originally specified); dimethoate is best for dealing with capsid, mealy bug, leafminers and scale.

Woodlice frequently cause trouble by feeding on the roots of seedlings and young plants in pots and boxes, attacking them through the drainage holes. Move the containers frequently, raise them off the standing surface with pieces of wood or pot and dust the base with HCH (BHC).

But do remember that use of most of these insecticides harms the beneficial insects as well, including the pollinators such as bees and hover-flies. If you keep an observant eye on your plants, you can halt most of these pests before they get out of hand by killing the first one or two. Where one greenfly is obvious, there will be ten hidden, or there will be shortly, if you don’t act immediately.

Grey mould (Botytis cinerea) infects through a previous injury and produces grey furry patches on leaves, stems and flowers, especially in cool, wet or humid conditions on practically any plant and can be treated with the systemic fungicide benomyl. Mildew produces white powder on leaves and flowers as well as buds and stems and causes most trouble from late summer onwards. Warmth, dewy nights and dry soil encourage its spread on plants; again use benomyl, or sulphur or dinocap.

Seedlings with stems reddish or black at soil level sometimes collapse; this is damping-off disease and is worst where seedlings are crowded. Use sterilized compost and water with Cheshunt compound to save remaining plants.

Weeds can cause a great deal of trouble in gardens but there are various modern chemical aids which kill them without harming cultivated plants growing nearby. Sodium chlorate is one which is watered in solution onto the soil so that it is absorbed by the plant roots; it remains effective for six months or more and is suitable for paths, drives, patios and all ground free of cultivated plants. Simazine is another of the same type, lasting twelve months, watered onto ground cleared of weeds, with the object of then keeping it clear. At certain dilution rates, recommended by the makers, it can be used round cultivated plants.

Dichlobenil is a third soil-acting weedkiller, applied dry in granular form to the soil to kill annual and perennial weeds. Like simazine, at certain application rates recommended by the makers, it can be used round some cultivated plants. It is effective for three to twelve months.

A second group of weedkillers consists of those sprayed on to the leaves and stems of weeds; they include those commonly known as 24D, 245T and MCPA. They are the so-called hormone weedkillers and will damage or kill any plant, not just weeds, as they are absorbed into the plant’s sap, circulated round it and dislocate the normal working of its metabolism. Morfamquat is another of these, specific to weed seedlings growing in grass, so is used on newly germinated lawns; it is also effective on small-leaved weeds such as suckling clover or speedwell. Dalapon is also a translocated type, specific to couch grass and other grasses.

The latest weedkiller is glyphosphate, translocated, but not a hormone type. Sprayed on to the top growth, it deals with annuals and perennials but does not have its effect through plant roots.

A third type of weedkiller is that which is sprayed onto leaves and stems, but which only affects those containing chlorophyll – the green colouring matter of plants. It becomes inactivated on reaching the soil. For annual and small weeds it is very useful; paraquat and diquat are the chemical names. Directions for use of all these weedkillers must be read and followed for safe, satisfactory results.

30. August 2011 by admin
Categories: Garden Management, Pest and Disease Control | Tags: , | Comments Off on Treating Pests and Diseases in the Flower Garden

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