File Name: compendium of onion and garlic diseases and pests .zip
A valuable and comprehensive treatise covering the many complex factors and effects involved in the movement of spores and pollen through the air.
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Content Content 1. Diseases - Fungal. Pests - Mites. See questions about Garlic. Garlic scapes. Garlic scape. Garlic sprouting. Harvested garlic. Field of garlic. Garlic flowerhead. Garlic plants. Garlic beginning to turn yellow. Garlic sprout emerging. Garlic curing. Common Pests and Diseases Diseases. Pale spots or elongated patches on leaves; gray-purple fuzzy growth on leaf surface; leaves turning pale then yellow; leaf tips collapsing.
Management Avoid planting infected sets; rotate crops to non-allium species for years; plant in well-draining areas and do not overcrowd plants; destroy all infected crop debris; apply appropriate foliar fungicides taking care to apply thoroughly to waxy leaves. Small water-soaked lesions lesions on leaves or stalk with white centers; which enlarge to become zonate and brown to purple in color with red or purple margin surrounded by yellow zone; large lesions may coalesce and girdle leaf, killing any tissue between the lesions and the leaf tip; severely infected foliage may die.
Disease emergence favored by wet foliage, with sporulation occuring during the night during periods of high humidity. Management Cultural controls include long rotations with non-hosts and the reduction of leaf wetness by planting in well-draining soil and timing irrigation to allow plants to dry adequately during the day; some fungicides are effective at controlling the disease but should be rotated for optimal control.
Cultivated garlic plant suffering from rust. Rust pustules on garlic leaf. Small white flecks on leaves and stems which develop into circular or elongated orange pustules; severe infestations can cause leaves to yellow and die. Favors high humidity but low rainfall; spores can be transported over long distances by wind. Management No resistance known; use only disease-free seed and plant in well-draining soil; control weeds around crop; apply appropriate protective fungicide.
Close up of white rot on base of garlic stem. Yellowing leaves of garlic plant caused by white rot infection. Older leaves yellowing; stunted growth; death of all leaves; fluffy white growth on base of bulb which spreads up bulb to storage leaves. Once disease is established the field is unusable for garlic production; fungus can survive in soil for 20 years and is one of the most damaging diseases of Allium crops worldwide, causing major crop losses.
Management Fungicide treatment may not be effective at controlling white rot under conditions which are favorable to the fungi's development and control may have to rely on cultural methods: avoid transferring soil or plant material between sites; treat seeds with hot water prior to planting; use a long term rotation with non-allium crops; apply appropriate fungicides if available.
Mosaic patterns on leaves; chlorotic mottling or streaks on leaves; stunted plant growth and reduced bulb size. Transmitted by aphids; infections can be latent and produce no symptoms; infection in garlic are often found alongside other viruses such as onion yellow dwarf. Management Plant virus-free cloves that were produced from meristem tip culture in virus-free conditions. Stunted plant growth; reduced stand; bulbs rotting in ground or in storage; pest is a cream-white, bulbous mite Damage to plants by bulb mites allows secondary invasion by other pathogens and can cause bulb rots.
Management Do not plant successive crops of onion or garlic in same location; allow field to fallow to ensure that any residual organic matter decomposes completely - crop residues can harbor mite populations; treating garlic seed cloves with hot water prior to planting may help reduce mite populations. Example of typical leafminer damage onion leaf. Thin, white, winding trails on leaves; heavy mining can result in white blotches on leaves and leaves dropping from the plant prematurely; early infestation can cause yield to be reduced; adult leafminer is a small black and yellow fly which lays its eggs in the leaf; larvae hatch and feed on leaf interior.
Mature larvae drop from leaves into soil to pupate; entire lifecycle can take as little as 2 weeks in warm weather; insect may go through 7 to 10 generations per year. Management Check transplants for signs of leafminer damage prior to planting; remove plants from soil immediately after harvest; only use insecticides when leafminer damage has been identified as unnecessary spraying will also reduce populations of their natural enemies.
Stunted or wilting seedlings; plant will commonly break at soil line if an attempt is made to pull it up; if infestation occurs when plants are bulbing, bulbs will be deformed and susceptable to storage rots after harvest; adult insect is a greyish fly which lays white, elongate eggs around the base of the plant; the larvae that emerge from the eggs are tiny and white and bore into the plant; mature larvae are about 1 cm 0.
Females can lay several hundred eggs during their week lifespan; insect overwinters as pupae in the soil. Management Management of onion maggots is heavily reliant on good snaitation; all onion bulbs should be removed at the end of the season as maggots will die without a food source; commercial onion growers must often rely on the application of appropriate granular insecticides and, in some cases, insecticide sprays are also required; home gardeners should try to remove any volunteer wild onion and chive plants as these can act as an infection source; floating row covers may help to protect plants and prevent females from laying eggs around plants.
Western flower thrips. Discolored, distorted tissue; scarring of leaves; severly infected plants may have a silvery appearance; insect is small 1. Onion thrips and western flower thrips have an extensive host range and can be introduced to garlic from other plants. Management Natural enemies include some species of predatory mite, pirate bugs and lacewings; avoid planting onion in close proximity to grain fields as thrips populations build up on these plant in the spring; overhead irrigation of plants may help reduce thrips numbers; apply appropriate insecticides at first sign of thrips damage.
Category : Nematodes. Stunted plants; root system lacks fine roots; round or irregular lesions on roots. Lesion nematode has one of the widest host ranges of any nematode; nematode enters the plant through the root epidermis and consumes cell contents. Management Hot water dips can be used to control nematodes in bulbs; crop rotation is not usually very effective at controlling lesion nematodes due to its extensive host range.
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The Epidemiology of Plant Diseases pp Cite as. Onions Allium cepa are grown worldwide as a vegetable for human consumption. They are harvested as dry bulbs, which are eaten raw or cooked. In certain countries e. Mexico they may be thinned when young for use in salads.
Onion Farming in Kenya Onions and especially onions grown from sets, are usually trouble cosmeticstandart. Marked progress has been made in the control of diseases of such crops as asparagus, cab- bage, beans, tomatoes, potatoes, peas, lettuce, celery, and spinach through the breeding and selection of disease-resistant strains and varieties. In many cases these resistant strains are exceptionally. Cultural control: Remove and destroy infected plant material. Work in the field only when foliage is dry.
Click here to download a PDF version of this spotlight. The bulb of an onion, the harvested product, develops as a result of the leaves of the onion plant producing sugars through photosynthesis, and these sugars then being translocated into the developing bulb. Anything, including disease, that impairs this process will impact the yield and quality of onion production.
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Compendium of Onion and Garlic. Diseases and Pests. SECOND EDITION. Edited by. Howard F. Schwartz. Colorado State University. Fort Collins. S. Krishna.Reply
Introduction. Howard F. Schwartz and; S. Krishna Mohan. Pages:1–7. https://doi.org// · Abstract · PDF. Preview Abstract.Reply
Front and back cover photographs by H.Reply
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