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)

Whilst 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.

Factsheet 21/15 Testing water for plant pathogens

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.

Factsheet 22/15 Methods of water treatment for the elimination of plant pathogens

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.

Factsheet 23/15 Hygiene and disease avoidance underpin the management of Oomycete stem and root rots

Good routine hygiene, facilitated by use of effective sterilant treatments, remains the backbone of any effective Oomycete disease management strategy. Simply put – clean plants, clean containers and media, clean water and clean kit mean a clean system and no disease. This may be ‘easier said than done’, but not impossible.
In this factsheet, the main factors in maintaining good hygiene and disease avoidance are outlined with reference to more detailed factsheets and reports where relevant.

Oomycetes and how they impact your business

Methods of water treatment for the elimination of plant pathogens

Testing and monitoring your water for Oomycete plant pathogens

Hard copies are free to AHDB Horticulture levy payers and dependent on your Associate package may be free or charged at a reduced rate. If you require a hard copy of this publication then please contact Hort.Info@ahdb.org.uk