Any damage to the root will interfere with the ability of the plant to take in the nutrients it needs to survive. The roots of a plant can start to rot because of cultural problems and because of fungus living in the soil. Damage to the plant will depend on how quickly the rot is identified and how much of the root system has been damaged.
Root rot is caused by bacteria and fungi that live in moist soil. Roots that are unhealthy because of poor drainage are especially susceptible to root rot. Too much or too little water are equally bad for healthy roots. Roots can also be damaged when the gardener digs too close to the plant and become susceptible to root rot.
Early signs that a plant may have root rot are color changes to the leaves. They may take on a dull appearance. Some may turn yellow; others may just wilt and fall off. In some cases, only half of the plant shows symptoms of root rot. This is especially true in trees and shrubs where only half of the root system is infected.
The length of time it takes for root rot to become fatal varies. Trees and shrubs can withstand the rot longer than smaller plants, sometimes taking years for the disease to become fatal. Once the smaller plant shows symptoms of root rot it's important to take immediate action as the disease can kill quickly.
If root rot is suspected, dig up the plant if possible to examine the roots. The feeder rootlets on a healthy root system are white. Roots that appear brown and mushy are diseased.
Check for rot on larger plants and trees that can't be dug up by peeling back the bark at the crown just above the soil. Sometimes root rot will move its way up the stem or trunk. Look for brown spots or streaks, or in advanced cases, cankers.
Nursery or greenhouse plants that have been diagnosed with root rot in the early stages can be treated with fungicides. Garden plants, shrubs and trees, however, won't receive much benefit from fungicidal treatments. Instead, improve the drainage around the plants.
Water the soil around the plant instead of letting the moisture fall directly on the plant stem or the tree trunk or crown. Allow the soil to become dry several inches deep before watering. Remove some of the soil from around the crown of the plant, without exposing any of the roots, to allow drying air circulation.
Finally, avoid using fertilizer on the plant when the weather is hot and dry.
Soil drainage problems are responsible for most of the stress to the root system, but the properly planned garden can help fight root rot.
In low areas where water tends to stand for longer periods, consider planting in raised beds. Give the plants good air circulation by spacing the plantings with consideration of potential growth.
Work organic matter into gardening areas to prevent soil from compacting and to aid in proper drainage.