In this article we will discuss about how to control pests and diseases of plants.
Introduction to Plant Management:
Plant management may include many things, but primarily Landscape designer has to deal with problems caused by plant pests and weeds, diseases and disorders. With careful planting and management majority of these problems may be avoided. Optimum growing conditions will ensure that plants remain healthy resisting diseases and pests. Good plant management involves spotting and preventing plant problems at an early stage when they can be treated more easily.
The number of pests, weeds and diseases can be minimised by following the basics of good plant hygiene practices. Weeding thoroughly, clearing up leaves, removing dead wood and pruning prevents the shelter and nourishment found by pests amongst weeds and debris. Pests and diseases cause most of the problems with plants.
Keeping plants healthy and growing strongly can help them resist problems. If plants are affected by pests or diseases, think carefully before going for chemical spray because some pests may not be hazardous. There are other alternatives to chemical treatment like biological and organic practices to preserve the natural ecosystem.
The following methods may be used to prevent pests and diseases to plants:
1. Prevention of Pests and Diseases:
The old proverb ‘prevention is better than cure’ applies well to plants and the fight against pests and diseases. Being vigilant and carrying out good hygienic practices can help preventing diseases and pests affecting the plants.
2. Landscape Hygiene:
Plant hygiene is one of the strongest weapons against the risk of pests and diseases. It means removing general debris and weeds on a regular basis to prevent them from becoming a refuge for pests and weeds. It is also important to remove and burn diseased material to stop it spreading to other plants. Plant pots and other equipment like knifes should be cleaned between use to avoid infections and diseases spreading from plant to plant.
3. Keeping Plants Healthy:
Strong and healthy plants are less likely to be infected than weak and unhealthy ones. Always purchase plants which appear vigorous and healthy with no signs of dying down, abnormally coloured leaves or poor root development. Consider buying disease-resistant varieties of plants. Always try to grow plants in the right conditions taking into account the soil type, texture and pH, the amount of sunlight and exposure to frost or wind. A plant grown in proper environment will have a much better chance of resisting any problems.
4. Plant Spacing:
Plant spacing is another important consideration in planting. Crowded planting will not only lead to plants competing for nutrients, air, water and light, but the close, humid surroundings encourage fungal disease. If a plant is badly damaged by disease or pests, it is better to destroy it to avoid infecting other healthy plants.
5. Natural Predators:
It is worth encouraging helpful natural predators to prevent plant problems because they help in pest control. There are a number of beneficial pest predators such as hoverflies, ladybirds, lacewings, frogs, toads and hedgehogs; which can control flies, beetles, grubs and slugs to a manageable level.
Pest predators may be encouraged by providing food plants and shelter. For example, hoverflies can be attracted by planting French marigolds, which they visit for nectar, while slug-eating ground beetles enjoy the shelter that can be provided with mulches and thick planting. Some birds, such as blackbirds, blue tits and thrushes enjoy feeding on insect’s pests, and may be encouraged with water, food in the winter, and nesting boxes.
Any controlling measures taken against pests should not harm the beneficial insects and animals. Persistent chemical control can wipe out the natural predators and making the plant more vulnerable to attacks and infestation.
Organic Control:
There has been a widespread interest in organic gardening because it uses as few manufactured chemicals as possible. The broad philosophy behind organic gardening is to take a holistic view of gardening.
This means:
1. Striving to conserve natural resources.
2. Understanding the interdependence of all life forms in the garden.
3. Avoiding pollution and health hazards.
4. Establishing a balanced ecological habitat for plants, animals and humans.
Organic control can be achieved in a number of ways using natural methods to help plants resist and recover from attack by pests and diseases.
1. Disease-Resistant Plants:
Some varieties of plants are specifically bred to resist certain pests or diseases. Check if there are disease or pest resistant varieties are available before buying plants.
2. Plant Health:
Keeping plants healthy can prevent a number of infections and infestations. Grow seedlings in pots so that they are protected properly. Make sure that only healthy and vigorous stock is planted out. Maintaining a good spacing between plants will allow them to grow without overcrowding. It also helps to prevent fungal diseases. Check plants regularly for signs of problems. A well-established infection is more difficult to deal with than one that is identified and treated early.
3. Mulching:
The addition of moisture-retaining protective covering can help to keep powdery mildew from crops and ornamentals.
4. Companion Planting:
Positioning certain plants together can reduce pest and disease attack. This is especially true of herbs, whose strong scents can repel pests or attract them away from more important planting. They can also attract beneficial insects that will act as natural predators. For example, chives, fennel and oregano all repel aphids, while coriander and mint attract natural insect predators.
5. Garden Hygiene:
Regularly removing and burning any infested or diseased plants or material will help to reduce the risk of the problem spreading. At the same time destroying or composting garden waste will prevent it from becoming a refuge for pests.
6. Crop Rotation:
Growing the same plant in one area for a number of years can lead to soil-borne pests and diseases of that plant. This may be relieved by rotating the crops and growing other botanically unrelated plants. Although crop rotation is most often carried out in the vegetable garden, it may also be used for annuals, bulbs and other plants.
7. Organic Treatment:
There are some chemical treatments that derive from natural sources, such as derris dust, soft soap, sulphur dust and pyrethrum (from the pyrethrum daisy). Although they are safe to use, they only act on contact with the disease or pest, so regular applications are needed.
8. Organic Traps:
Traps may be easily put together to catch a wide range of pests.
(a) Trap earwigs in inverted flower pots.
(b) Attract wireworms to cut potatoes or carrot buried 10-15 cm (4-6 in) deep.
(c) Use beer traps to catch slugs.
(d) Attract greenhouse whitefly to a yellow card smeared with grease.
Biological Control:
Biological control involves keeping down pests by the introduction of natural enemies: predators, parasites and diseases. This technique may be essential in the greenhouse, where pests may have developed immunity to chemicals.
a. Control in the Greenhouse:
The biological control is very attractive and it is becoming more popular. There are now several different pest predators available to kill whiteflies, red spider mites, mealy-bugs, leaf miners, scale insects, thrips and vine weevils. Biological controls are particularly useful in the greenhouse. Its controlled, warm environment and excellent light allows predators and parasites to breed faster than pests.
It is important to introduce the control before plants are heavily infested otherwise it may take a number of weeks to become effective. The majority of parasites and predators need temperatures of at least 21°C (70°F) for at least part of the day and good sunlight. They should be released onto the affected plants in the cooler part of the day on the day of occurrence. Some predators are strong fliers, so open doors and windows need to be netted to prevent them from escaping.
b. Control in the Garden:
Many of the biological controls are only suitable for use in the greenhouse or conservatory. There are other biological controls which may be used outdoors. These are natural predators like birds, hedgehogs and frogs which should be encouraged to visit the garden. Harmful insects can be reduced by spiders, frogs, ants, wasps and birds, whilst hedgehogs, shrews, frogs and toads feed on many plant pests. The centipede is also a useful ally, feeding on soil-dwelling pests.
Chemical Control:
If pests and diseases cannot be prevented or treated by using proper cultivation methods and organic control, then it may be necessary to treat them with chemicals. A careful combination of organic and chemical techniques may provide the best solution to difficult and recurrent problems.
1. Pesticides and Fungicides:
Pesticides are used to kill insects, mites and other pests. Fungicides are used to control diseases caused by fungi. Both types work either by contact action or systemically. Contact pesticides kill pests when they are hit by the chemical during spraying or when they later crawl over a treated plant.
Systemic pesticides are drawn up through the roots or taken in through the leaf pores and then transported by the sap stream throughout the entire plant. This makes pesticides of this type particularly useful for sap-suckers. Although contact fungicides kill germinating fungal spores and prevent further infection, they have little effect on established fungal growths. A systemic fungicide is needed to kill fungi in the plant tissues.
2. Ingredients and Formulations:
Pesticides and fungicides can be bought in a range of different formulations like concentrated liquids, dusts, powders, smoke and pre-diluted sprays. Always avoid making more concentrates than necessary because they may become ineffective within 24 hours. It is best to buy ready-made sprays for smaller areas. These sprays last as long as undiluted concentrates and do not need to be mixed.
3. Chemical Safety:
While working with chemicals, it is necessary to minimise any harm to the user or to the environment. Always read the information on the label, carefully follow the instructions and never exceed the recommended dose. Any pesticide which may be potentially harmful to bees and other beneficial insects should only be sprayed in the late evening when they are no longer working the flowers. Carefully follow the instructions for disposal of excess chemicals. They should never be poured down sinks, drains or watercourses.
Plant Care:
Plants damaged by diseases or pests should be fed with a general fertilizer after an attack to restore them to health. Use a foliar feed for root damage. Root damage makes uptake of nutrients from the soil difficult.
1. Pests:
A garden pest is any animal or insect causing damage to plants. The damage may be by chewing leaves, sucking sap, removing bark or tunneling through leaves, fruits or stems. Many pests can also damage plants by spreading viral or fungal diseases. Some other pests like aphids, coat the plant in a sticky substance encouraging the growth of sooty moulds.
2. Weeds:
Weeds are plants growing where they should not grow. They are often fast-growing, persistent and survive in almost any soil. Their drawback is that they fight with cultivated plants for space, light, water and food. Ornamental cultivated plants can also be classed as weeds, if they are persistent for their site or self-seed freely throughout the garden.
3. Types of Weeds:
There are two major types of weed- yearly and perennial.
i. Yearly weeds complete their entire lifecycle within one year setting seed that germinates freely. It is important to eradicate V annual weeds when they are seedlings before they can reproduce.
ii. Perennial weeds can survive year after year. They produce deeply penetrating tap roots, rhizomes or tubers for long-term survival. Many have the ability to regenerate from very small pieces of root. It is essential that no pieces are left behind when cultivating.
4. Perennial Weeds:
Perennial weeds form a storage system in their roots or stems preserving for many years. They are very difficult to eradicate as they have a number of methods to ensure their survival- They may produce seed that may be dispersed to reach new ground as well as the surrounding area.
Many can regenerate even if the top is removed by means of underground fleshy roots, rhizomes or bulbs. Perennials can survive through the winter by storing food in their roots or by storing food in stems and branches. It is essential to remove and destroy the underground fleshy roots, rhizomes and other storage organs to prevent re- growth of perennial weeds.
Digging, tilling and mechanical cultivation often break up the roots of these weeds allowing them to survive and restore themselves. This is particularly true of those weeds with very deep roots. The most practical and effective form of control is to use systemic weed-killers. The plant absorbs the chemical and transports it through its entire system eventually killing the whole weed.
5. Preventing Weeds:
The best way to control weeds is to prevent them from establishing in the garden. There are a number of ways to do this, which will reduce the need for weeding later.
(a) Clearing the Soil:
Always clear the site of all annual and perennial weeds before planting. This may be done chemically or by hand. If the site is invaded with perennial weeds, treat the whole area with a weed-killer before planting season. Eradicate annual weeds by spraying or forking out before planting. It may be possible to treat soil invaded by perennial weeds by laying a carpet or light-excluding black polythene over the site. Then leave it undisturbed for at least two years. This can starve out perennial weeds.
(b) Keeping Plants Healthy:
Strong and vigorous plants will be able to compete with weeds much more effectively than weak ones. Healthy plants forming a leafy canopy will discourage weeds from establishing beneath their spreading foliage.
(c) Mulching:
A protective covering layer around plants blocks out light preventing weed seeds from germinating. Organic mulches need to be 10 cm (8 in) thick to be totally effective. Thinner layers (5 cm/2 in) may allow the occasional perennial weed to grow through but they are easy to remove. Avoid using garden compost or manure.
This often contains weed seeds. Use only leaf mould, peat substitute or processed bark. Inorganic mulches are more effective at suppressing weed growth. A layer of black plastic sheeting will prevent annual weeds from establishing. Crops and other plants may be grown through the plastic sheeting by simply cutting a cross in the plastic and positioning desirable specimens through it. The unattractive plastic surface may be concealed with a layer of bark or gravel.
(d) Planting Ground Cover:
There are a number of ground cover plants which will grow in dense carpets and suppress the germination of weed seeds. Plant them in weed-free soil to ensure good growth.
(e) Companion Planting:
Some vegetable crops help to suppress or clear the ground of weeds. This needs to be done for a few seasons to exhaust the rhizomes. Potatoes compete well with annual weeds and may be grown to help retain weed-free ground for later planting.
(f) Controlling Weeds:
Weeds may be controlled by manual, mechanical or chemical means. The choice of methods will usually depend of the type of weed and its location. Yearly weeds respond well to tilling, while perennial weeds need to be treated with weed-killer.
i. Manual Control of Weeds:
In many cases to control weeds in borders, vegetable gardens and small areas without harming neighbouring plants is by manual weeding. It may be either by hand or by using a hoe or a fork. Yearly weeds may be removed from the ground by hand-weeding or by shallow hoeing before they set seed.
This should be done on a dry, sunny day, so that the weeds are easily loosened from the soil and dry out quickly. Use a sharp hoe with a back and forth sliding motion so that weeds become severed from the stems, preventing further development. Tilling will defeat most weeds and the reservoir of seeds in the soil layer will be exhausted if carried out regularly.
Shallow rooting perennial weeds should be removed using a fork, so that the roots may be lifted intact. All of the rhizomes, roots or bulbils should be removed from the soil so that the weed does not have a chance to re-establish itself. Some perennials are particularly difficult to eradicate and may be resistant to many weed-killers.
It may be necessary to control the growth of these weeds by repeatedly cutting down their foliage. Although new growth will regenerate quickly from their large food reserves, infestations can be considerably reduced in a few years. This technique is useful for perennials as regular mowing will finally weaken the plants.
ii. Mechanical Control of Weeds:
Mechanical aids may be used against weeds. Rotavators (rotary cultivators) are suitable for dealing with yearly weeds in unplanted areas and between rows of vegetables. They should not be used where perennial weeds are growing. They will chop the roots and distribute them across the area multiplying as new plants. A flame gun is a useful alternative to weed-killers. They may be used in areas such as paths and paving. Take extra care when using a weed burner so that nearby plants are not damaged.
iii. Chemical Control of Weeds:
Weed-killers are the most effective solution for controlling weeds. They may be the only way of dealing with some persistent perennials.
There are three major types of weed-killer application:
1. Foliage activated:
Applied by spray and enters the plant through its leaves or stem. Works by contact or systemic action.
2. Soil Activated:
Applied to the soil, and enters the plant through its roots.
3. Selective:
Most kill broadleaved plants, but leave narrow-leaved grasses unharmed. Some leave ornamental plants while killing grassy weeds.
When working with weed-killers, it is essential to work carefully to minimise harm to the user or to the environment. Always wear protective clothing when mixing or applying chemicals, and never work in windy weather when there is a risk of spray being blown back or across to nearby plants.
Also carefully follow the instructions for disposal of excess chemicals. They should not be poured down sinks, drains or watercourses. There are many ready-to-use weed-killers, which come with their own spray head attached. These are convenient to use.
For larger areas it may be more economical to buy a concentrate to dilute later. Always read and follow the instructions on the packet when using weed-killers. While using chemicals to clear and replant an overgrown area, make a note of how much time is needed to leave the ground before replanting.
The best time of year to apply a systemic weed-killer is in late spring when the plant has started to grow and the plant’s transport system is active. It is often worth cutting back large perennial weeds a few weeks before spraying.
They produce healthy new foliage which will take in the weed-killer better. After applying weed-killer, it may take several weeks before the weed shows signs of dying. Reapply the product if new growth appears, and then dig out and remove dead weeds.