Symptoms and outcomes
Plants' roots are not typically visible as they are below the surface of the soil, so the symptoms of root rot are often only apparent when the disease is advanced. Roots of plants affected by root rot may turn from firm and white to black/brown and soft. Affected roots may also fall off the plant when touched. The leaves of affected plants may also wilt, become small or discolored. Affected plants may also look stunted due to poor growth, develop cankers or ooze sap.
Prolonged root rot may lead to death of the plant. In extreme cases, plants affected by root rot may die within 10 days. Root rot is usually lethal although it is treatable. An affected plant will not normally survive, but may potentially be propagated.
Root rot is primarily caused by poor drainage of damp soil, overwatering or a poorly functioning root system. Prolonged exposure to excess water causes waterlogging, which interferes with aeration of the roots, leading to low oxygenation and decay. Planting in a dense soil, such as garden soil, can also lead to root rot. Rot can spread from affected roots to other ones. Excess or insufficient light and fertilizer can also increase the chance of a plant developing root rot.
Aside from waterlogging, many cases of root rot are caused by pathogens, such as the water mold genus Phytophthora; particularly the species P. cinnamomi. Other commonly responsible pathogens include Pythium, Rhizoctonia, and Fusarium. Spores from root rot causing agents do contaminate other plants, but the rot cannot take hold unless there is adequate moisture. Spores are not only airborne, but are also carried by insects and other arthropods in the soil. The wet environment of waterlogged soil promotes the growth of these fungi, allowing them to cause the disease. Garden soil often contains spores of pathogens so it is not advised to be used as a potting medium for indoor house plants.
Other causes of root rot include:
- Armillaria, which cause white root rot disease and shoestring root rot
- Rhododendron root rot
- Texas root rot
- Rosellinia necatrix aka Dematophora necatrix
- Scytinostroma galactinum aka Corticium galactinum
Treatment and prevention
The most effective treatment for root rot is prevention such as destruction of affected plants. It is recommended that, in localised cases of root rot, the affected plant simply be destroyed and the surrounding soil replaced.
Treatment options depend on the extent of the rot. To treat root rot, is recommended to replant the affected plant in fresh soil with good drainage to avoid standing water. It is also recommended to gently wash diseased roots and remove all brown, soft parts of the roots with a sterilized pair of scissors or a tool such as a pulaski for larger roots. Rapid treatment and replanting of root rot is imperative to stop the disease spreading to the rest of the affected plant or to other plants and to allow plants to form new roots. Chemical treatments, such as fungicides, chloropicrin and methyl bromide may also be used to limit progression of the disease but must be specific to the responsible pathogen.
Some sources claim that cinnamon powder is an effective treatment for reducing spread of root rot, when applied to exposed tissue after removal of diseased tissue. Cinnamon is also claimed to act as a potential fungicide.
To prevent recurrence and progression of root rot, it is recommended to only water plants when the soil becomes dry, and to plant the plant in a well-drained pot. It is recommended that pots used for diseased plants should be sterilized with bleach to kill potential spores. This allows the plant to drain properly and prevents fungal spores affecting the plant. It is recommended to keep the soil around the plant as dry as possible and to pry back the soil to allow proper aeration.
Root rot can occur in hydroponic applications, if the water is not properly aerated. Aeration is usually accomplished by use of an air pump, air stones, air diffusers and by adjustment of the frequency and length of watering cycles where applicable. Hydroponic air pumps function in much the same way as aquarium pumps, which are used for the same purpose. Root rot and other problems associated with poor water aeration were principal reasons for the development of aeroponics.
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