Climate and soil type in relation to Phytophthora attack on pine trees

[First paragraphs...]
In 1953 and 1954 in the Auckland district and in 1956 throughout the North Island, Pinus radiata on farms and urban properties suffered from a spectacular disease causing death or defoliation. Symptoms were caused by a group of soil fungi belonging to the genus Phytophthora.
Species of Phytophthora are amongst the most serious soil-borne parasites of plants. Infection is normally associated with asexual reproduction and liberation of motile zoospores from sporangia occurs only in actual moisture. This dependence on water is characteristic of diseases caused by Phytophthora spp. It explains why they are commonly associated with poorly drained situations, with irrigation or with wet seasons.