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Pests & Disease Symptoms Controls

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Identifying Pests and Diseases
Every gardener encounters different garden pests and diseases, some of which can have a devastating effect. As long as you can identify them and take the appropriate action immediately, many pests and diseases need not cause too much harm or devastation to your garden plants.

Identifying Pests and Diseases

Some pests and diseases are potentially very harmful. Others may cause serious problems only if a plant is badly stressed or already under attack from something else. Use the following chart to identify the major problems and to learn how to deal with them effectively.

Slugs and Snails
Both these pests feed mainly at night and after rain. Smooth-edged holes appear on foliage, stems, and petals. Both pests may tunnel into corms, bulbs, and tubers, making large holes. Silvery slime trails are often found nearby. Use nematodes to control slugs. Cultivate soil to expose eggs, and remove debris. Reduce the use of organic mulches. Lure slugs to inverted citrus peels, collect the peels and discard.


Caterpillars: Many garden plants are attacked by caterpillars, the larvae of butterflies and moths. Leaves, soft stems, and occasionally flowers develop holes as they are eaten. Some caterpillars spin a fine web around the leaves. Pick off the caterpillars. Prune out damaged stems and heavily webbed areas. Spray with the biological control Bacillus tburingiensis or with a suitable pesticide.

Greenhouse whiteflies: Greenhouse whiteflies are most common in greenhouses but may also be found outside in hot weather. Leaves are discolored and distorted and may be covered with sticky excreta, which attracts black sooty mold growth. Introduce the parasitic wasp Encarsia formosa into greenhouses and conservatories. Alternatively, spray with insecticidal soaps, or other insecticides.

Weevils: Adult beetles cause notching around leaf edges. The white grubs attack many plants, particularly those in containers. They eat and tunnel into roots, tubers, and corms. In mid-spring or early autumn, biological control drenches of nematodes to warm, moist soil. Gather and destroy adult beetles and grubs.

Rust: Various fungi are responsible for rust infections. They are most severe in damp or moist weather and on soft, lush growth. Orange, yellow, or brown spots appear on leaves, mostly on the lower surface. The upper surface may have yellow blotches. Remove infected leaves promptly. Improve air circulation around the plants. To decrease humidity, avoid wetting the foliage. Spray with a suitable fungicide.

Leaf spot: Various bacteria and fungi cause leaf spots. If this is caused by bacteria, spots may be irregular with a yellow edge. Fungal spots have concentric rings and an area of tiny fungal fruiting bodies. Black, brown, or gray spots may cover the leaves. Most leaf spots do not cause serious problems and may develop only on plants that are in poor condition. Remove badly infected leaves, and improve the plant’s growing conditions. Spray with a suitable fungicide for fungal leaf spots.

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Powdery Mildew: These mildews cause a white, powdery layer of iungal growth to appear – usually in distinct patches or spots, which then coalesce. A few mildews are pale brown and felty. Leaves, stems, and flowers may be attacked, and may wither and die. Powdery mildew thrives in humid air. Prune to improve air circulation, and keep plants well watered and mulched. Avoid wetting leaves. Spray with a suitable fungicide.

Earwigs: Many plants are attacked by these pests, particularly dahlias, chrysanthemums, clematis, peaches, and certain annuals. Young leaves and petals are eaten, especially during the summer. In extreme cases, a plant can be severely damaged. Make traps with rolled-up corrugated cardboard or flower pots stuffed with straw gather and destroy the pests. Alternatively, spray at dusk with an insecticide.

Toadstools: Toadstools are usually seen in lawns in the autumn, especially during mild, damp spells. Toadstools are usually short¬lived and rarely survive the first frosts. They may form “fairy rings,” which cause grass to become discolored. If the grass is unharmed, simply brush off the toadstools as soon as they appear, preferably before their caps open. If they reappear, they may be growing on buried organic debris, such as old tree roots; dig these out.

spider mites

Spider Mites: Several species of spider mite occur on garden and greenhouse plants. A common and trouble¬some species is the two-spotted, or greenhouse, spider mite. In severe cases, leaves may turn brown and die. Fine webbing may appear on affected plants. Control spider mites with predatory mites. Allow adequate ventilation, and damp down frequently. Spray with insecticidal soap or miticide.

Botrytis: Many plants are susceptible to this fungus. Fuzzy, gray patches develop on infected areas. Plant tissue becomes discolored and deteriorates, and there may be extensive dieback. White or yellow circles appear on tomato skins. Clear out all plant debris. Remove and destroy infected tissue promptly. Avoid injuring the plants, and improve air circulation around them by pruning. If necessary, spray with a suitable fungicide.

Aphıds: Aphids feed by sucking sap and may cause plant parts to become discolored and distorted. Their sticky excreta may encourage the growth of black sooty mold. Aphids can be many colors; some are covered with white, waxy wool. Natural or introduced predators and parasites may help to reduce numbers. Spray with a strong stream of water from a hose to dislodge them, or with insecticidal soap, or insecticide.

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Viruses: Many viruses have a wide and diverse host range. Symptoms can vary. Stunting, poor growth, leaf yellowing (usually as flecks, ring-spots, streaks, or mosaic patterns), distortion, and flower-color changes are the most common symptoms. Viruses are spread by handling or other mechanical injuries, and by pests such as aphids, thrips, and nematodes. Some are seed-borne. Avoid damaging plants, and disinfect pruning tools frequently. Control virus-carrying pests, and remove infected plants promptly.

Clubroot: Clubroot affects many brassicas, including broccoli, brussels sprouts, cabbage, radishes, and rutabagas, as well as some ornamentals. Symptoms include distorted and swollen roots, and poorly developed, often discolored, stunted foliage. Improve soil drainage and add lime to discourage the slime mold responsible for clubroot. Raise plants in individual pots, and plant out when they have a strong root system. If possible, choose resistant cultivars.

Foot and Root: Rot Bedding plants, seedlings, beans, cucumbers, tomatoes, and peas are particularly susceptible. Soil- or waterborne fungi cause discoloration of stem bases, which shrink inward. Plants grow poorly and ultimately wilt, wither, and die. Observe strict hygiene: use sterilized commercial soil mix, clean trays and pots, and tap water. Do not overwater or crowd plants. Water seeds and seedlings with a copper-based fungicide. Remove affected plants immediately.

pest header

Scab: These are most common on apples, pears, and Pyracantha. Gray or black, scabby patches develop on affected plants. Leaves and fruit are commonly affected, but stems may be attacked, too. Leaf puckering and fruit distortion often occur. Avoid overhead watering. Rake up and dispose of affected leaves, and prune out infected shoots. Keep the center of plants open by pruning carefully. Spray with a suitable fungicide.

Codlıng Moths: Apples and pears may be attacked by the larvae of codling moths. Holes, often surrounded by brown, powder¬like droppings, appear on ripe fruit. The codling moth larvae feed in the core of the fruit, tunneling out when mature. Hang pheromone traps in trees from late spring to midsummer to catch male moths this will reduce the number of codling moth eggs that will be fertilized by the miles. Spray with a suitable pesticide.

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Cabbage Root Flıes: Many brassicas, including cabbage, rutabagas, cauliflower, and Brussels sprouts, may be attacked by this pest. Seedlings die, and plants may wilt and become discolored. Larvae measuring up to in (9 mm) long tunnel into the roots of crops. Place collars of carpet padding, roofing felt, or cardboard around the base of each plant when it is transplanted Alternatively, dust transplanted brassicas and seed rows with a suitable soil insecticide.

Carrot u Rust Flies: Carrots are the most common host to this pest, but other plants may also be attacked, including celery and parsley. Carrot rust fly larvae tunnel into roots, causing rust-brown lesions on roots and plants. Plants may develop discolored foliage. Erect a plastic barrier around crops to keep out female flies or protect a whole crop with a row cover. Avoid handling crops, since the smell of the leaves may attract adult flies. Treat seed rows with a suitable insecticide.

Flea Beetles: Seedlings of brassicas, leafy vegetables, radishes, stocks, nasturtiums, and wallflowers are particularly vulnerable. The tiny beetles feed on leaves, making numerous holes on the upper surfaces. Hot, dry summers encourage this pest. Flea beetles overwinter in plant debris, so clean up debris thoroughly to avoid damage. Use sticky traps Warm soil before sowing seeds, and water regularly to encourage rapid, strong growth. Use a suitable insecticide.

Wireworms: Many plants may be attacked, particularly potatoes and other root crops. Perennials, annuals, seedlings, and bulbous plants may also be damaged. Young plants may wilt, wither, and die as wireworms tunnel into their roots. Recently cultivated soil, or an area recently converted from grass, is most likely to harbor these pests. Bury carrot and potato pieces as bait. Lift root crops as early as possible. Apply a suitable insecticide to infested soil.

Peach Leaf Curl: Peaches, nectarines, and ornamental and edible almonds may be attacked by this fungus. Affected leaves pucker and become blistered and swollen, then turn red or purple; as spore layers develop on the surfaces, the leaves turn white. Erect a plastic shelter over susceptible trees to prevent the air- or waterborne spores from l. Pick off affected leaves. Spray with a copper fungicide in midwinter, and again two weeks later. Spray again when the leaves fall.

Pests & Disease Symptoms Controls