Determining Plant Damage Produced by Fungus, Bacteria, Viruses, and Nematodes
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By Agnes Farside
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In order to determine which living factors such as fungus, bacteria, virus, or nematodes are causing plant damage, a gardener must play detective and look for clues in the way of signs and symptoms. It is not always easy for a gardener to determine if plant damage is caused from a bacteria or a fungus, so close observation and sometimes even record keeping of the changes the plant is going through is needed.
Fungus
Since each fungus has its own distinct cell structure, pathologists can make easy identification of the type of fungus that is damaging a plant. Ranging in size from microscopic to being able to be seen by the naked eye, signs of fungal damage can be seen in leaf or stem spots, which are usually circular, dry, and brownish-black in color. Sometimes the spots may have red, yellow, or purple halos. Root rot is a type of fungus that infects the root tissues leading to wilting in the above ground shoots.
Bacteria
Unlike a fungus, bacteria will attack plants through wounds or natural openings, reproducing rapidly to kill plant cells. Some bacteria such as bacterial leaf spot may be of a slimy or sticky texture and/or produce a rotten odor. One distinct clue on identifying bacteria leaf spots is that the color of the spots is usually uniform. Bacteria gall can produce toxic material resulting in abnormalities of roots, leaves, and/or stems. Some bacteria cause yellowing, wilting, or dieback of leaves and stems by plugging water-conducting tissue.
Viruses
Viruses infect host plant cells enabling them to infect other cells within the plant. They can cause cells to grow rapidly or slowly, causing stunting, and/or plant death. Viruses also cause leaf and flower distortion, and prevent the flow of chlorophyll, which will result in mottled colors of green and yellow. Plants can contract viruses through mites, insects, fungus, nematodes, abrasions, grafting, and other propagation techniques. Viruses are hard to identify and may require a gardener to obtain a microscope for identification and verification.
Nematodes
Nematodes are round-shaped, microscopic worms that feed on plant tissue. More often, they will be found on or in the plant’s root tissue, with these being appropriately named root nematodes. Root nematodes damage roots, stunt plant growth, and can even cause galls or knots. Shoot nematodes are discovered inside leaves with damaged seen at the base of older foliage. A wedge-shaped, discolored area on a leaf is another sign of Shoot nematodes.
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Author Bio Box: Agnes Farside
 http://www.associatedcontent.com/user/110407/agnes_farside.html
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