From there it should drain to a second pond from which irrigation water is pumped. Ponds should be cleaned out occasionally so that ample depth for settling remains. This approach is not totally effective, however. Phytophthora inoculum is disseminated in most irrigation systems used at nurseries. To control Phytophthora inoculum that is disseminated in these systems, nurseries can install a slow-sand filtration system.
Some nurseries store water in two separate pond systems, each used for a particular container area.
The second pond contains runoff from the first production area. The greatest potential for pathogen recirculation, therefore, is associated with the second system. Crops that are more resistant to Phytophthora root rots and salinity should be irrigated with water draining from the production area where susceptible plants are produced. It is important to monitor chlorides and salinity in water. High concentrations of salts increase root rot and can break down resistance in plants to these diseases.