Identifying Bacteria And Viruses In Your Garden
Bacteria
Bacteria are one-celled organisms that can cause a variety of diseases in plants, many of
them with symptoms similar to those caused by fungi. A foul odor is one symptom of bacterial diseases that is not often associated with fungal or viral diseases and is easy to distinguish.
Bacteria cause a variety of blights, characterized by plant parts that wilt and die, leaving blighted stem tips with leaves attached. Rot may set in after the blight occurs. Bacteria can also cause leaf spots and stem, crown, or fruit rots. They can also cause swellings and wilts. Unlike fungal rots, bacterial rots are often accompanied by a foul odor; afflicted parts may be filled with slimy, rotted tissue. Since they are single celled, bacteria don’t produce the threadlike web of hyphae or the spore-bearing stalks characteristic of fungi.
Bacteria can enter plants only through existing openings. But since plants have so many little natural holes in their leaf surfaces, this requirement doesn’t slow bacteria down in the slightest. Even the smallest bruise on a stem or leaf makes a tiny dead spot, or extra doorway for bacteria. They can also enter through puncture wounds caused by insect feeding.
Basic control of bacterial diseases is quite similar to fungal diseases. When you spot the first sign of a bacterial infection, remove all plants or parts of plants that show symptoms. If you have a newly built hot compost pile, one that will heat to 160F, you can discard infected plant parts near its center to kill the bacteria. Otherwise, dispose of infected plants in the trash, or burn them.
For soil-borne diseases, dig and dispose of the infected soil as well. Also, try not to damage plants by digging into crowns or brushing into or tearing foliage; damaged plant tissue provides an open invitation to bacterial diseases. For vegetables and other annuals, establish a rotation system to avoid planting susceptible plants in the same spot year after year.
Viruses
Plant pathologists have identified more than 300 viruses and virus-like organisms that attack
plants. Viral organisms are much smaller than bacterial cells. Although they cause a broad
range of symptoms, they are spread in similar ways, and control measures for all virus diseases are similar. In some cases, symptoms of viral disease may closely resemble symptoms of nutrient deficiencies: Plant analysis is the only sure way to diagnose the problem.
Viruses can cause stunting and abnormal growth patterns such as leaf cupping or twisting. Other symptoms include leaves that are mottled or streaked with yellow or have ring-shaped spots. Viruses are only active when inhabiting living hosts like your garden plants. They reproduce by stimulating their host cells to create more viruses. When the host dies, the virus becomes inactive. However, many dormant viruses can remain capable of infecting new hosts for as long as 50 years.
Viruses are most frequently transmitted by insects, called vectors. The most notable virus vectors are aphids and leafhoppers. Some viruses are carried from one plant to another in an insect’s saliva. These pathogens are particularly dependent upon sucking or chewing insects for transportation. Viruses may also be carried on an insect’s feet and can also be spread mechanically, when they are picked up and moved around by a breeze, or even by the gardener’s hand, clothing, or tools, especially pruning tools.
Since many common viruses can remain dormant but capable of infection for long periods of time, digging and destroying an infected plant in your garden doesn’t really do any good unless other infected host plants are removed from the area, including weeds and plants in the neighbor’s yard. Unlike bacteria, a hot compost pile does not usually kill viruses. Remove virus-diseased plants from the garden and surrounding areas and bury them in a faraway spot, burn them, or put them out in sealed containers with your household trash.
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