Above-ground symptoms often do not develop until the root decay is well advanced. They are not specific to Phytophthora root rot, and merely indicate that the plant is having trouble taking up water and To grow well, plants need a wide range of nutrients in various amounts, depending on the individual plant and its stage of growth. The three key plant nutrients usually derived from soil are nitrogen, phosphorus and potassium, while carbon, oxygen and hydrogen are absorbed from the air. Other vital soil nutrients include magnesium, calcium and sulphur. Most garden soils contain enough nutrients to promote healthy plant growth.
Symptoms include wilting, yellow or sparse foliage and branch dieback. In many cases the symptoms get progressively worse until the plant dies. A common symptom in conifers is a gradual fading in the colour of the foliage, from a vibrant to a dull green, through to greyish and finally brown.
Below-ground examination of the roots, collar and stem base of an affected plant will reveal a poor root system. Many of the fine, feeder roots will have rotted away. Some or all of the larger roots will also show evidence of decay – they will be brown or black internally, softer than normal and may break easily. Because Phytophthora species are microscopic organisms there will be no evidence of the pathogen itself in association with the decay, unlike with honey fungus where a prominent white fungal growth may be found below the bark. Very similar root symptoms to those of Phytophthora infection can be caused by prolonged waterlogging, and the situation is further complicated by the fact that Phytophthora root rot is frequently associated with Describes soil or potting compost that is saturated with water. The water displaces air from the spaces between soil particles and plant roots can literally drown, unless they are adapted to growing in waterlogged conditions. Waterlogging is common on poorly drained soil or when heavy soil is compacted.
In severe infections Phytophthora invades the collar or stem base of the plant, causing a brown or black discoloration below the Bark is the outermost layer of woody plants (trees, shrubs and woody climbers). It is several cells thick and provides protection against physical damage, disease and environmental stresses. Bark comes in a wide variety of colours and patterns, and these can help gardeners when identifying plants. The fissures and crevices of bark on older plants also creates valuable habitat for many garden creatures as well as lichens and small plants.