Phytophthora: managing outbreaks

Phytophthora root rot can cause heavy losses in a garden, but there are steps you can take to limit its impact. Here we explore the options available and how best to implement these measures in your garden.

Phytophthora root rot on yew

Phytophthora root rot on yew

Quick facts

  • Phytophthora root rot is caused by a micro-organism
  • Spores swim through wet soil to reach new plant roots
  • Infected soil spreads on footwear or when moving plants
  • Disease is more likely in stressed plants
  • The spores can persist in soils for several years

Remove, contain, clean and drain

Phytophthora root rot is a soil based disease that can kill a wide range of plants. It is one of a number of causes of woody plant death. If you have had the disease confirmed follow these initial steps;

  1. REMOVE: Remove sick-looking plants that do not appear to have enough strength to continue to grow.
  2. CONTAIN: Avoid moving infected soil around the garden. Unwanted soil should be bagged securely and sent to landfill.
  3. CLEAN: Prevent spread of the disease to other areas of the garden using good garden hygiene. Tools, shoes and boots can carry disease around the garden. Either clean footwear at the edge of the diseased area, walk away only on dry, hard surfaces or change shoes and carry the footwear away for cleaning. Cleaning shoes/boots with hot, soapy water is usually sufficient for this task. Tools can be cleaned with a disinfectant such as Jeyes Fluid, used according to its labelling.
  4. DRAIN: Improve drainage and aeration. Prevent excess water flowing into affected beds. This could be caused by run-off from hard surfaces, a leaking drain, an over-flowing water butt, or a soak-away. Use a fork pushed full depth into the soil to create aeration holes. Rocking the fork backwards and forwards slightly can be helpful. Consider brushing horticultural (unsalted) sand into these holes if they appear large enough, which will keep the holes open to the air for longer. In areas with compacted soil, digging over the area and incorporating organic matter will help to open up the soil. Avoid further compaction by working in dry weather.

Replant the area

You're now ready to put some plants back into the area.

Replanting

  • Replant with resistant plants, as listed on our Phytophthora host list and do not plant too deeply (ensure the root collar is exposed)
  • Replant into a raised bed or mound to aid good drainage
  • Avoid forming a soil ‘bucket’, or sump, when planting. Holes dug into compacted or clay soils and filled with a better draining compost can cause water to pool at the bottom of the hole. Avoid this effect by forking the sides and base of the hole

Alternative planting schemes

  • Rethink the garden scheme if drainage cannot be achieved. Examples of alternative schemes to use include installing a pond or a bog garden
  • If the soil surface drains freely, putting the area down to a lawn or growing ornamental grasses are good options

Plant care

Simple measures can help reduce further plant losses to Phytophthora root rot;

  • Avoid overwatering and maintain good plant health. Provide adequate fertiliser for each species and prune at suitable times of year to minimise stress on the plants
  • Check that none of the plants have soil or mulch piled up around their stems. If necessary expose a small amount of the root collar to the air and to help keep them dry
  • Use a dry mulch such as grit or shingle, rather than using a mulch that will hold moisture


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