Oomycetes

The stem and root-rotting oomycetes are a large group of related fungus-like plant pathogens, including the genera Phytophthora, Pythium and Aphanomyces, which cause significant plant losses and yield declines in a wide range of plants across all sectors of horticulture.

Although diverse, this group of pathogens do share a number of characteristics that make certain generic practices, such as the treatment of irrigation water and the implementation of simple hygiene measures, highly effective for their management and control. Three factsheets are presented here explaining:

1. How to test water for the presence/absence of oomycete plant pathogens (21/15).
2. The current range of available water-treatment technologies – their pros and cons, and their efficacy against oomycetes (22/15).
3. Effective hygiene procedures for reducing the incidence and spread of oomycete stem- and root-rots (23/15).

While focused on oomycete stem- and root-rot diseases, the procedures and systems described in the accompanying factsheets and videos below have broad applicability to the practice of good horticulture and generally effective disease management and avoidance.

Water for irrigation can easily become contaminated with potential plant pathogens and, whether a new source of water is being considered or there are concerns with  the current supply such as possibly contaminated storage tanks or the occurrence of suspicious disease outbreaks, water testing is essential for guiding management  decisions.

However, the approach to testing can strongly influence the value of the results.

This factsheet explains the appropriate testing that is currently available to properly assess the disease risks and outlines interpretation of results, together with the questions to ask a prospective test provider.

Many plant diseases can be introduced to, and spread within, cropping systems by contaminated irrigation water, especially those caused by species of Pythium, Phytophthora and Fusarium. Fortunately, it is possible to eliminate or significantly reduce this disease threat by treating water before irrigation use. There is a wide range of effective water treatment methods available and selection of an appropriate method or system for a particular horticultural concern is very much a case of different concerns are suited to different methods.

In this factsheet the current most readily available water treatment methods are outlined, together with some emerging technologies and some considerations to assist individual nurseries in the selection of an appropriate technology.