What Is Specific Apple Replant Disease (SARD)?

What Is Specific Apple Replant Disease?

Specific apple replant disease apple treeSpecific Apple Replant Disease (SARD) occurs when apple trees are planted in soil where similar species of fruit trees have been grown previously. Surviving for up to 15 years within dead wood and other organic matter in the affected soil, SARD can severely impact the health, yield and growth of apple trees.

Affecting all varieties of apple tree – each to varying degrees – SARD occurs worldwide. With the specifics of its causes, and the severity of its impact, varying from region to region, and country to country.

While this disease is known as Specific Apple Replant Disease when affecting apple trees, it’s also commonly referred to as ‘sick soil syndrome’, and can affect a wide range of other perennial fruits.

What Causes Apple Replant Disease?

While the exact causes of SARD are still largely unknown, it’s thought to occur when soil pests and pathogens build up in the soil over the lifetime of the initial tree planting.

This build up is generally slow, so by the time this reaches critical levels, existing trees are usually old and strong enough to cope. It isn’t until young, infant apple trees are introduced to this hostile soil that these pathogens begin to have an impact.

The exact organisms that contribute to this build-up vary wildly between regions the world over, though there are a number of soil-based suspects on the list. These include fungal pathogens, fungal root diseases and nematodes – eelworms specifically – and various viruses. As well as bacteria such as Actinomycetes (filamentous bacteria) and fungi including Rhizoctonia, Pythium, and Phytophthora. Other soil factors have also been shown to cause SARD, including improper Ph levels and insufficient phosphorus.

The severity of SARD can also depend on the soil density, with sandy soils showing a greater sensitivity to SARD than heavier soils. The density of the affected species’ root levels in the soil, and the amount of time without crops or trees can also play a role.

The disease isn’t just limited to apple trees, either. It also affects roses (Rose Sickness), as well as a number of other fruit trees. These include:

  • Cherry
  • Citrus
  • Peach
  • Pear
  • Plum
  • Quince

What Are The Symptoms Of Apple Replant Disease?

Apple trees affected by SARD present numerous symptoms, most commonly seen in the stunted growth of trees compared to those planted in healthy soil. Leaves will often remain small, and light green in colour, while the fruit these trees produce will be lesser in both quantity and quality.

Affected apple trees will also show limited root growth, and the existing root system will be small, and show signs of decay or discolouring. In severe cases, this can result in the death of the tree, or the entire orchard.

What Can I Do To Treat Apple Replant Disease?

General Tips For Combating Apple Replant Disease

Swap Soil

If you’re a nursery or orachard and find that you need to replant your apple trees in the same location – or if planting in a new location isn’t viable – then soil replacement can be an effective method for smaller sites.

It’s important to ensure that this replacement soil is of a high quality, and has not been used for old apple or fruit tree planting in the past.

When replacing soil, it’s recommended that you do so with an area that’s slightly larger than the full spread of the tree’s roots. And, as always, it’s important that any old, ‘contaminated’ soil is then disposed of appropriately.

Apply Fertilisers

When planting your trees, apply Nitrogen rich fertilisers such as Hoof And Horn or Sulphate Of Ammonia.

Use Resistant Strains

There are a number of strains of fruit trees and roses that are shown to be more resistant to replant disease than others. When deciding on the right trees for your orchard, keep an eye out for:

  • Apples on M27
  • Cherries on ‘Colt’
  • Plums on Myrobalan B
  • Roses on Rosa Laxa

Meanwhile, look to avoid the following strains that are more susceptible to replant disease:

  • Roses on Rosa Canina
  • Flowering Cherries on Prunus Avium

Combating Apple Replant Disease For Growers & Nurseries

There is little that can be done to help apple trees that have been affected by apple replant disease after planting. As always, this means that prevention is a far more cost effective – and efficient – method for dealing with SARD than finding a possible cure.

Multiple studies have been conducted into the effectiveness of methods used to treat SARD, which continue to highlight that soil fumigation remains the only viable, reliable method of commercially guaranteeing future orchard performance, as well as the healthy growth of apple trees following replanting.

While it’s clear that soil fumigation remains your best bet in the fight against SARD, there are some other preventative measure you can use to ensure you’re doing your best to keep this disease from taking hold.

Have Your Soil Tested

While there are no tests available for SARD specifically, soil tests will provide vital information on Ph levels and soil fertility. It’s recommended that this soil testing and analysis be carried out a year before planting. As this allows for sufficient time to determine fertiliser requirements as well as whether any adjustments are required to the soil Ph levels.

It’s also recommended that testing be carried out for pathogenic nematodes: a common occurrence in SARD-affected soil.

Remove Old Plant Matter

Ensure you remove old plant material as soon – and as thoroughly – as possible. Taking special care to remove all traces of roots during this process.

Grow ‘Break Crops’

When possible, avoid replanting similar species in the same spot. For many, this may not be practical, but growing a ‘break crop’ can often play a vital role in prevention, as certain investigations have shown.

Following the ‘Pomes and Stones’ rule can also prove effective. This involves avoiding following a ‘Pome’ fruit (such as apples or pears) with a fruit from the same group. Instead, following this with a ‘Stone’ fruit (such as plum, cherry, peach or almond).

This method is not guaranteed, however. As these trees can still be susceptible to non-specific replant disease. Which affects Pomes trees that are planted after Stone crops, and vice-versa. Believed to be caused by a combination of nematodes and fungi.

Fumigate your soil.

Soil fumigation chemicals lead the fight against SARD, with a number of treatment options available depending on the crop in question.

Methyl Bromide was once commonly used to control apple replant disease in the 90’s, however this has since been phased out to make way for more modern alternatives in recent times. Chief among these being Chloropicrin. A solution which has been shown to be an effective combatant in the war against SARD.

Download the PDF on Chloropicrin Soil Fumigation to Resolve SARD.

Note! If soil fumigation is used in the prevention of SARD, it’s important to ensure non-fumigated and fumigated soil isn’t mixed, as this can reintroduce the disease into the otherwise healthy soil.

Further Studies, Reading & Resources On Apple Replant Disease

  • Controlling Replant Disease In Stone & Pome Fruits In North East United States | Read More
  • Growing Apple Orchards In Replant Sites In Washington State | Read More
  • The Control Of Apple Replant Disease In Nova Scotia, Including Chloropicrin | Read More
  • The Role Of Microbial Ecology In The Cause & Control Of Apple Replant Disease | Read More
  • The Role Of Soil Microflora & Pratylenchus Penetrans In Apple Replant Disease | Read More
  • The Fungi Associated With Apple Replant Sites | Read More
  • Cherry & Apple Replant Disease And Their Control With Soil Fumigation | Read More
  • The Effects Of Nematodes, Fungi & Bacteria Of Apple Trees Grown In Apple Replant Disease Affected Soil | Read More

Images via Redwoods Garden Centre


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