Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Apple -- Replant Disease
 
Cause: A complex of fungi, bacteria, and nematodes in addition to nonbiological factors including poor soil structure, moisture stress, low or high pH, insufficient available phosphorus, and cold stress. This is a serious, common cause of poor growth of apple trees planted in old apple orchards. Tree growth is suppressed the first year and for the life of the orchard. Compared to healthy trees, yields can be reduced by 20 to 50% and fruit quality is also lowered.

Soil analysis is recommended to detect nutrient deficiencies and to determine whether lime is required to adjust pH. There is no effective treatment of replant disease once trees are planted.
Symptoms: Apple replant disease has no definite symptoms other than trees' poor growth the first few years after transplanting. Vigorous young trees planted in a problem site stop growing in early summer. Affected trees leaf out each spring but produce little or no shoot growth. Leaves are often smaller and lighter green than leaves on vigorous trees. Few new lateral or feeder roots are produced, and existing roots become discolored and deteriorate.
Cultural control:

  1. Avoid by not planting apples on the same ground where an old apple orchard has recently been removed. Rotations out of pome fruit for 5 to 8 years are advised.
  2. Adjust soil pH if too high or low.
  3. Plant as early as possible in the spring taking care not to skip important preplant operations.
  4. Mixing monoammonium phosphate fertilizer (11-55-0 or 11-51-0) with the planting hole soil at a rate of 1 g/liter of soil is no longer recommended since the high salt concentration can burn roots. Although there is an initial growth increase, the practice has no overall benefit after 5 years.
  5. Provide proper management, from plant nutrition to irrigation.
  6. Use resistant rootstocks if and when available.

Chemical control: Preplant fumigation. Consult or hire a professional applicator to be sure it is done safely and effectively.

  1. Methyl bromide as a fall treatment is highly recommended. It is most effective if injected into a well-plowed or ripped site with warm (50 to 60°F) and dry (50% water holding capacity) soil. Restricted-use pesticide.
  2. Metam-sodium products such as Metam CLR (42%), Sectagon 42, or Vapam HL. Vapam HL can be used at 56 to 75 gal/A. Use in enough water to penetrate only 3 ft. Remove as much tree root debris as possible before application. Trees adjacent to the treatment site may be injured. 48-hr reentry.
  3. Telone C-17 (Telone plus chloropicrin) at 32.4 to 42 gal/A depending on soil type and depth of penetration. Do not use Telone alone; it has not been effective in eastern Washington. 5-day reentry. Restricted-use pesticide.
Biological control: Soil replacement with new soil or well-prepared, steamed planting soil mixture, or soil replacement with a ratio of 1 part peat to 2 parts planting-hole soil. Data indicate that a hole 6 foot square or more and 3 ft deep gives best long term control.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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