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Ministry of Agriculture, Food and Rural Affairs

Apple Replant Disease

Apple Replant DiseaseClick to enlarge.

Beginner

Scientific Names
Biological factors include a complex of several fungal pathogens including Cylindrocarpon, Phytophthora, Pythium spp. and Rhizoctonia, as well as parasitic nematodes and bacteria.

Identification

  • Stunting of the tree with short internodes,
  • Small and light green rosette leaves,
  • Small root systems and decayed or discoloured roots,
  • Few new lateral or feeder roots are produced,
  • Affected trees leaf out in the spring but often produce little or no shoot growth,
  • Severe disease results in the death of young trees and entire orchards,
  • Trees in orchards not killed by replant disease often bear fruit two to three years later than healthy tree and rarely attain comparable yields.

Often Confused With

  • Zinc deficiency - Zinc deficiency’s characteristic symptom is rosetting of leaves at the tips of the shoots as they first leaf out. Application of foliar zinc products reduces the symptoms. Replant disease can have leaf rosettes but also have small decayed root systems.
  • Phytophthora root rot - Phytophthora root rot infected trees have small root systems with decayed roots but are limited to areas where there is moisture stress. Infected trees wilt and collapse suddenly after bud break. Replant disease can have small decayed root systems but the above ground symptoms are gradual and reflect the replant site.

Period of Activity
Symptoms appear during the growing season.

Scouting Notes
During regular scouting in orchard blocks make note of sections where young trees show stunted growth, short internodes and rosette leaves.

Thresholds
None established.

Advanced

Apple trees that do not establish well or fail to establish when planted on a site previously grown with apples are often considered to be suffering from apple replant disease. Although thought to occur in sites replanted after removing very old fruit trees, replant disease has been documented to occur within three years of establishing an orchard on new ground. The causes and symptoms of replant disease vary from region to region and even from site to site. Biological factors play a major role in this disorder.

Scientific Names
Biological factors include a complex of several fungal pathogens including Cylindrocarpon, Phytophthora, Pythium spp. and Rhizoctonia, as well as parasitic nematodes and bacteria.

Identification
Symptoms of replant disease on affected trees include stunting, short internodes, rosette leaves, small root systems and decayed or discoloured roots which results in poor productivity. Often affected trees have fewer lateral roots and root hairs. Vigorous young trees affected by apple replant disease often stop growing in early summer. Affected trees leaf out in the spring but often produce little or no shoot growth. Leaves are generally small and light green in colour as compared to the leaves on vigorous trees. Few new lateral or feeder roots are produced, and existing roots become discoloured and deteriorate. Severe replant disease results in the death of young trees and entire orchards. Trees in orchards not killed by replant disease have delayed fruit bearing and reduction in overall yield.

Often Confused With

  • Zinc deficiency - Zinc deficiency’s characteristic symptom is rosetting of leaves at the tips of the shoots as they first leaf out. Application of foliar zinc products reduces the symptoms. Replant disease can have leaf rosettes but also have small decayed root systems.
  • Phytophthora root rot - Phytophthora root rot infected trees have small root systems with decayed roots but are limited to areas where there is moisture stress. Infected trees wilt and collapse suddenly after bud break. Replant disease can have small decayed root systems but the above ground symptoms are gradual and reflect the replant site.

Biology
The disease and causal agent of apple replant disease are not well understood. A complex of various fungi, bacteria and nematodes are associated with replant disease. In addition to biological factors, other non-biological factors such as soil pH, moisture stress (too much and too little), soil compaction, toxins, soil structure, heavy metals and insufficient availability of nutrients (particularly phosphorous) are also implicated as part of the complex of factors contributing to replant disease. Although abiotic factors play an important role in this disease, research showing dramatic tree growth in response to soil pasteurization and fumigation suggests this disease is primarily a biological phenomenon. The current theory is that a complex of several fungal pathogen combinations including Cylindrocarpon, Phytophthora, Pythium spp. and Rhizoctonia, as well as parasitic nematodes and bacteria, are involved with replant disease.

Period of Activity
Symptoms appear during the growing season.

Scouting Notes
During regular scouting in orchard blocks make note of sections where young trees show stunted growth,short internodes and rosette leaves.

Thresholds
None established.

Management Notes

  • Prevention of replant problems is much easier and more successful than control. There is very little that can be done to correct replant problems once the trees are planted.
  • Root-lesion nematodes are often associated with other biological factors contributing to replant disease. Take a soil sample for nematodes at a site before establishing a new young orchard particularly if the site was planted with apples or other fruit trees in the past.
  • The causes of apple replant disease on different sites are highly variable. Not all soils respond in the same way to the various pre-plant treatments, and a treatment that is beneficial in one orchard may have no effect in another.
  • The following cultural controls help avoid apple replant disease.
  • Avoid planting apples on the same ground where an old apple orchard has recently been removed. Rotating out of pome fruit for several years (two to eight years) is advised.
  • Adjust soil pH if too high or low prior to planting with a lime or sulfur application.
  • Plant as early as possible in the spring taking care not to skip important pre-plant operations.
  • Provide adequate nutrition and irrigation as indicated by soil and tissue tests, and soil moisture monitoring equipment.
  • Use root rot resistant rootstocks.
  •  Research to reduce apple replant disease has some success with:
    • nematode-suppressing cover crops, plowing down various types of cover crop residue containing biologically active ingredients;
    • poultry manure at a rate of 4%(v/v) (equivalent to 8.9 tonnes/ha including tree rows);
    • rootstocks resistant to Phytophthora (e.g. CG.30, CG.6210 and CG.16) at sites where Phytophthora is a contributing factor;
    • staggering planting rows to avoid planting directly in old tree sites.
  • Currently, chemical control of apple replant disease is accomplished by use of pre-plant soil fumigation. The use of fumigants may not be available in the future because of their negative environmental impact.
  • For information on soil fumigants, see OMAFRA Publication 360, Guide to Fruit Production.