Use a water source free of Phytophthora
The environment for propagating susceptible plants is generally favorable for disease development; thus the need for a source of clean water. Irrigation water from wells or municipal sources is considered to be free of Phytophthora. This is the best water source to use in propagation facilities (cuttings, seed beds, liners).
Phytophthora spores can be found in surface water from streams or reservoirs, especially if the water flows through diseased areas. Of all the water sources, recycled water from nurseries has the greatest chance of containing Phytophthora.
Irrigation water is recycled, through drainage systems and ponds, in most container nurseries and in some field nurseries. Drainage systems move excess irrigation water and rain away from crops and to a storage reservoir.
Drainage systems can include surface ditches and/or subsurface drain tiles, depending on the layout of the growing area and the natural slope of the land.
Drainage systems are a critical link in the Phytophthora disease cycle. Phytophthora spores from diseased plants will move with drainage water and end up in storage reservoirs. They can survive for a while and might be irrigated back onto healthy plants.