In this second part of a report on Phytophthora root rots, Dr Aileen Reid (Development Officer Horticulture, Dept of Agriculture, WA) looks at disease management and control methods.
Disease management
It is extremely difficult to eradicate Phytophthora from an infested site, especially when perennial crops are involved. If it is known the disease is limited to a particular area, or if the crop is being grown in soil-less media in bags or containers, then it may be possible to remove the soil to as great a depth as possible. While the spores may be predominantly in the root zone, they may have been carried to a depth of a metre or more in soil water. The more soil can be removed, the better.
Soil or media may be treated to reduce the pathogen. The difficulty is achieving treatment at depth. Most soil sterilants only penetrate to a depth of about 30cm at best. Steam is a chemical-free option but treatment in the field relies on having the correct equipment, access to power and a suitable water supply. The use of steam permits pasteurisation instead, which uses a slightly lower temperature and so allows a range of “friendly” microflora to remain. The presence of this beneficial microflora usually helps to limit the growth of pathogens if and when they are reintroduced, as opposed to chemical fumigation which eliminates both harmful and beneficial organisms. 

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