Pink Rot (Phytophthora Erythroseptica): Potato & Carrot Disease & Prevention Techniques

What Is Pink Rot?

Pink Rot And Its Effect On Potato & Carrot Crops

A potato suffering from pink rotPink Rot (Phytophthora Erythroseptica) is an aggressive plant pathogen which is particularly prevalent in moist soil during hot, dry years.

First recorded in Ireland, the disease has since extended to countries across the world – including New Zealand – where it mostly affects potatoes (including Kumara and Sweet Potato), as well as in carrots.

Phytophthora Erythroseptica is also related to other varieties of pink rot, some of which are known to affect raspberries, tomatoes, asparagus and strawberries.

The disease itself is considered an ‘oomycete’, which means that it follows a similar cycle to other Phytophthora species. Oospores, sporangia, and zoospores infect any part of the potato plant found below the ground, whether healthy or not. Though it’s worth noting that the presence of a wound greatly increases the severity of the infection.

When affected tubers are cut open and exposed to air, they turn a salmon pink – hence the name – before decaying to a brown and then later turning black.

Pink Rot isn’t an easy disease to eradicate. It’s known among most growers as a particularly hardy pathogen, surviving up to seven years in moist soil. This combination of hot weather and damp soil sees the pathogen at its worst, as moisture makes it easier for the infectious zoospores to move through the soil, and infect potato tubers.

Signs & Symptoms Phytophthora Cactorum May Be Affecting Your Potato & Carrot Crops

Pink Rot (Phytophthora Erythroseptica) generally attacks the underground part of the plant which, upon closer examination, should reveal brown or blackened stolons or roots on mature affected plants. In more severe cases, the infection can cause chlorosis in the leaves, as well as stunting and wilting symptoms in the above-ground stems.

This penchant for affecting potato tubers and tubers alone makes this a tricky disease to spot, though there are some other warning signs to look for. Infected tubers can often be spotted at time of lifting, where the soil will stick firmly to the affected surface. On closer inspection, the tuber itself will appear dark, wet or spongy, oozing a clear colourless liquid and giving off a very distinct, sweet smell.

The skin may also be loose, and have blackened lenticels. There may be occasions where tubers exhibit further signs, though this is often due to another soil pest or pathogen infecting the tuber alongside the Pink Rot.

More often than not, tubers remain intact and may even appear sound at the time of harvesting and loading, but will quickly break down in storage, usually rotting from the heel end first. In fact, while infection can occur early on in the potato’s development, the majority of diseased tubers are infected while in storage.

This usually occurs during handling, particularly if otherwise healthy potatoes are bruised during the handling process. This weakening or damage to the outer skin allows the pathogen an easier point of entry, and a higher chance of successfully taking hold.

Phytophthora Erythroseptica Prevention & Management Techniques

Ways To Prevent & Manage Phytophthora Erythroseptica In Potato & Carrot Crops

Common Prevention Techniques

  • Ensure your soil has good drainage.
  • Be mindful not to oversaturate your soil while irrigating.
  • Harvest when the soil is dry, and your potatoes have a good skin set. This will help eliminate the possibility of entry points being created for the pathogen during the handling process.
  • Handle any potatoes with care to limit the amount of wounds in the skin, which is a common entry point for the pathogen.
  • Ensure your potatoes are stored in a dry, well-ventilated, cool area below 5-10° Celsius.

Common Management Techniques

Pink Rot is a difficult pathogen to control, so the combined efforts of multiple prevention techniques are often required to effectively subdue the disease.

  • Remove infected potatoes and debris from your fields.
  • Rotate your potatoes with other crops like Legumes or Brassicas.
  • Choose Pink Rot resistant varieties whenever possible.
  • Effective soil fumigation techniques and products like Metalaxyl and chemicals like it disrupt RNA polymerase and prevent transcription, and is often used around a month before harvest.

Images via Images via Ontario Ministry of Agriculture, Food, & Rural Affairs

  • Contact Information

    Leicesters Soil Fumigation
    6 Waitane Place
    PO Box 4036
    Marewa, 4143
    Napier, New Zealand

    Phone: +64 6 843 5330
    Fax: + 64 6 843 5158

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