Apple — Crown and Collar Rot

Cause: Phytophthora cactorum and other species, a
soilborne fungus-like microorganism. Crown rot is a disease of the rootstock
portion of the tree; collar rot is a disease of the scion portion. Both are
serious diseases of apple and other orchard trees in British Columbia,
Washington, and Idaho, and have become a problem in Oregon orchards with
clonal rootstocks, principally Malling Merton 106. Crabapple can also be
infected.

The fungus survives primarily as oospores in soil, organic
debris, or infected tissues. Oospores produce a swimming spore stage
(zoospores) when soils are at or near saturation. Zoospores swim to and
infect roots. Movement within roots to the root crown is greatest between
pink bud and shoot elongation.

Symptoms: In early fall, an affected tree shows bronzing,
purpling, or yellowing foliage of one or more limbs, accompanied by bark
reddening. There is a reduction in the size of leaves and terminal growth.
Examination at the root crown or collar after scraping away the soil reveals
dead bark. The cambium will be orange-brown to red-brown, eventually becoming
dark brown instead of white. A distinct margin may separate healthy from
infected tissues. In many cases, the tree may be completely girdled before
its condition is noticed. Fire blight symptoms may be similar when confined
to the rootstock.

‘Antonovka’, ‘McIntosh’, and ‘Wealthy’ apple seedlings and
M9 clonal rootstocks have shown high resistance to collar rot. Moderately
resistant: MM111, M2, M7, M26, ‘Golden Delicious’, ‘Delicious’, and ‘Rome
Beauty’. Susceptible: MM104 and MM106.A

Cultural
control:

1. Plant on a raised bed to help keep water away from
   trunks.
2. Avoid overirrigation.
3. During summer, examine root crowns of trees for
   collar rot and scrape off diseased tissues. Leave root crowns exposed to
   the air until late fall.
4. Avoid wounding root crowns. If a wound is made, keep
   it uncovered and open to the air for the remainder of the season.

Chemical
control: Apply before symptoms appear,
especially in orchards favorable for disease development. No chemical will
revitalize trees showing moderate to severe crown rot symptoms. Although
resistance has not been reported, alternate materials so resistant fungi do
not develop quickly.

1. Agri-Fos at 1.25 to 2.5 qt/A. Do not combine with a
   copper-spray program for control of other diseases. 4-hour reentry.
2. Aliette WDG at 2.5 to 5 lb/A. Spray foliage to run
   off. Follow manufacturer’s directions for timing of spray. Do not apply
   within 14 days of harvest or more than 20 lb/A per season. Do not
   combine with a copper spray program for control of other diseases.
   Phytotoxicity may result if applied within 1 week of a copper spray.
   12-hr reentry.
3. Fixed copper products. Use 4 gal solution as a drench
   on the lower trunk of each tree in early spring or after harvest. Do not
   use if soil pH is below 5.5. Not considered organic since application is
   to the soil.
1. Champ Formula 2 at 2.75 pints/100 gal water. 24-hr
   reentry.
2. Copper-Count-N at 4 qt/100 gal water. 12-hr reentry.
   
3. Cuprofix Disperss at 5 lb/100 gal water. 24-hr
   reentry.
4. Kocide DF at 4 lb/100 gal water. 48-hr reentry.
5. Nordox 75 WG at 2.5 lb/100 gal water. 24-hr reentry.
   
4. Fosphite at 1 to 3 quarts/A. Do not use copper
   products within 20 days of treatment and do not use spray adjuvants. May
   also be injected into trunk. 4-hr reentry.
5. Phostrol at 2.5 to 5 pt/A. 4-hr reentry.
6. Ridomil Gold SL at 0.5 pint/100 gal water. Apply
   diluted mixture (based on trunk size measured at 12 inches above the
   soil line) around each tree trunk. Apply once at planting or in spring
   before growth starts. Apply again in fall after harvest. 48-hr reentry.

References:
Jones, A.L. and H.S. Aldwinkle. 1990. Compendium of Apple and Pear Diseases.
1990. St. Paul, MN: APS Press.

Content
edited by: Jay W. Pscheidt on January 1,
2008

Cause: Phytophthora cactorum and other species, a
soilborne fungus-like microorganism. Crown rot is a disease of the rootstock
portion of the tree; collar rot is a disease of the scion portion. Both are
serious diseases of apple and other orchard trees in British Columbia,
Washington, and Idaho, and have become a problem in Oregon orchards with
clonal rootstocks, principally Malling Merton 106. Crabapple can also be
infected.

The fungus survives primarily as oospores in soil, organic
debris, or infected tissues. Oospores produce a swimming spore stage
(zoospores) when soils are at or near saturation. Zoospores swim to and
infect roots. Movement within roots to the root crown is greatest between
pink bud and shoot elongation.

Symptoms: In early fall, an affected tree shows bronzing,
purpling, or yellowing foliage of one or more limbs, accompanied by bark
reddening. There is a reduction in the size of leaves and terminal growth.
Examination at the root crown or collar after scraping away the soil reveals
dead bark. The cambium will be orange-brown to red-brown, eventually becoming
dark brown instead of white. A distinct margin may separate healthy from
infected tissues. In many cases, the tree may be completely girdled before
its condition is noticed. Fire blight symptoms may be similar when confined
to the rootstock.

‘Antonovka’, ‘McIntosh’, and ‘Wealthy’ apple seedlings and
M9 clonal rootstocks have shown high resistance to collar rot. Moderately
resistant: MM111, M2, M7, M26, ‘Golden Delicious’, ‘Delicious’, and ‘Rome
Beauty’. Susceptible: MM104 and MM106.A

Cultural
control:

1. Plant on a raised bed to help keep water away from
   trunks.

1. Avoid overirrigation.

1. During summer, examine root crowns of trees for
   collar rot and scrape off diseased tissues. Leave root crowns exposed to
   the air until late fall.

1. Avoid wounding root crowns. If a wound is made, keep
   it uncovered and open to the air for the remainder of the season.

Chemical
control: Apply before symptoms appear,
especially in orchards favorable for disease development. No chemical will
revitalize trees showing moderate to severe crown rot symptoms. Although
resistance has not been reported, alternate materials so resistant fungi do
not develop quickly.

1. Agri-Fos at 1.25 to 2.5 qt/A. Do not combine with a
   copper-spray program for control of other diseases. 4-hour reentry.

1. Aliette WDG at 2.5 to 5 lb/A. Spray foliage to run
   off. Follow manufacturer’s directions for timing of spray. Do not apply
   within 14 days of harvest or more than 20 lb/A per season. Do not
   combine with a copper spray program for control of other diseases.
   Phytotoxicity may result if applied within 1 week of a copper spray.
   12-hr reentry.

1. Fixed copper products. Use 4 gal solution as a drench
   on the lower trunk of each tree in early spring or after harvest. Do not
   use if soil pH is below 5.5. Not considered organic since application is
   to the soil.

1. Champ Formula 2 at 2.75 pints/100 gal water. 24-hr
   reentry.

1. Copper-Count-N at 4 qt/100 gal water. 12-hr reentry.
   

1. Cuprofix Disperss at 5 lb/100 gal water. 24-hr
   reentry.

1. Kocide DF at 4 lb/100 gal water. 48-hr reentry.

1. Nordox 75 WG at 2.5 lb/100 gal water. 24-hr reentry.
   

1. Fosphite at 1 to 3 quarts/A. Do not use copper
   products within 20 days of treatment and do not use spray adjuvants. May
   also be injected into trunk. 4-hr reentry.

1. Phostrol at 2.5 to 5 pt/A. 4-hr reentry.

1. Ridomil Gold SL at 0.5 pint/100 gal water. Apply
   diluted mixture (based on trunk size measured at 12 inches above the
   soil line) around each tree trunk. Apply once at planting or in spring
   before growth starts. Apply again in fall after harvest. 48-hr reentry.

References:

Jones, A.L. and H.S. Aldwinkle. 1990. Compendium of Apple and Pear Diseases.
1990. St. Paul, MN: APS Press.

Content
edited by: Jay W. Pscheidt on January 1,
2008