Phytophthora is a soil-borne fungal disease caused by Phytophthora sojae. This pathogen causes seed rots, pre- and post emergence damping off of seedlings and stem rot of plants at various growth stages. Disease development is favored by soil temperatures is above 60oF and high soil moisture.
Symptoms of Phytophthora disease are often overlooked. As this disease typically starts with the roots, the signs remain relatively hidden while the infection is spreading.
When the diagnosis of a Phytophthora disease contamination is late, it will likely result in the loss of the tree, plant, or even an entire crop. Symptoms of the disease include:
• Blackening of the lower trunk or stem
• Stunting of foliage
• Wilting and discoloring of foliage
• Dieback of shoots and foliage
• Interveinal chlorosis (typical of nutrient deficiency)
• Soft, brown roots instead of firm, white ones
How to prevent:
• Ensure that soils, growing media and standing areas are well drained
• Ensure that water used for irrigation is free from Phytophthora. Cover storage tanks to prevent contamination from soil and plant debris.
• Consider the use of filters (e.g. slow sand filtration) or sterilisation (e.g. UV, chlorine) where water is re-circulated or known to be contaminated
• Use new pots, trays, etc. or at least treat any re-used items with a disinfectant
• Inspect bought-in plants. If possible, have a quarantine area where bought-in stock can be held and monitored for disease development for a few weeks
• When propagating, take cuttings from healthy plants only. Avoid taking cuttings of nursery stock close to the ground, as these could be contaminated by soil or compost containing Phytophthora
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