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quarta-feira, 27 de março de 2013

Common Signs And Treatment For A Phytophthora Infection

Among the most common causes of decay of the roots and stems of a wide variety of trees and shrubs is Phytophthora. There are around 100 species of Phytophthora that have been described and each specie affects over 1000 different plant species. Still, experts believe that there are approximately 100-500 species that remain undiscovered.This plant-damaging Oomycete is capable of causing tremendous economic losses on crop growers worldwide. In fact, it was responsible for the potato blight which resulted to the Great Irish Famine in 1845 to 1849.

It is difficult to detect plant infection until the root decay has become severe. Root decay may also indicate that the plant is not taking enough water and nutrients because of a poorly-functioning root system. Factors such as water logging, root diseases and drought may also cause similar foliar symptoms.

Other symptoms include yellow or sparse foliage, wilting and branch dieback. In most cases, the symptoms get worse which eventually cause the plants to die. In conifers, the common Phytophthora root rot symptom is a slow fading in the color of the foliage, from vibrant to dull green, then grayish and finally, brown.

Examining the roots, stem base and collar of an affected plant typically shows a poor root system. Most of the fine roots may have rotted completely. Some of the larger roots may show signs of decay. Decaying roots are usually black or brown internally, soft and breaks easily. Phytophthora also releases long-lived resting spores from the decaying roots which may cause soil contamination in the vicinity of the infected plant for several years.

Since Phytophthora is a microscopic organism, it is hard to find any evidence that the fungus is indeed responsible for the root rot. Unlike other plant pathogens such as honey fungus that leaves a noticeable white fungal growth below the bark of a plant. Most growers also often mistake the rotting root symptoms of a Phytophthora infection to prolonged water logging. Typically, a laboratory examination is required to find out whether the root problem is caused by Phytophthora or water logging.

Remember that there are thee main ingredients for a disease to occur - host, fungal source and a suitable environment. Removing one or more of these elements prevents a disease outbreak or stops a disease from spreading. Phytophthora does not develop as often or may not be as severe on properly drained environment. On other hand, it can thrive severely in heavy clays and poorly drained soils as well as in areas where run-off water or rain water collects around the roots. It is important to prevent the growth of this disease as chemicals are usually ineffective in eliminating the disease after the symptoms have become severe and obvious.

Make sure to buy disease-free plants from your local nursery. Do not purchase plants that don't have a normal green color, looks wilted in the morning and evergreen plants with serious winter defoliation or dark and discolored roots. Avoid planting plants that are susceptible to root rot.

The spread of Phytophthora can also be reduced with the use of fungicides. However, these chemicals may not totally eliminate the fungus in the infected plants. For individual plants, treat around 10 sq ft. of soil surrounding the plant. For large shrubs, treat at least 20 to 30 Ft of soil.


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