[NAFEX] Apple question

dmnorton at royaloakfarmorchard.com dmnorton at royaloakfarmorchard.com
Mon Apr 30 09:23:11 EDT 2007

The material on the apple tree trunk could be sooty mold, a saprophyte that lives on the surface of the branches and does not become directly parasitic. Left unchecked, it can interfere with the photosynthetic activity of the tree in some cases, weakening it to attack by parasitic organisms. It is easily controlled with insecticidal soap. The photo was a bit small and difficult to see, but there could be winter injury on the trunk.  Damage to trunks or limbs caused by wounds, cankers from other disease, insects or winter injury can provide an entrance for black rot fungus to invade and become established. The cankers first appear as reddish or pinkish, brown sunken areas in the bark. Cankers often remain small and superficial but can sometimes enlarge up to half a meter in length along the infected limb killing the bark which eventually cracks. Cankers that developed last winter could be providing the inoculum which could also develop into frog eye leaf spot.  

Ap[ple scab could be another possibility.  The fungus causes circular, olive-black spots on the leaves, fruit, and young fruit stems and trunks.  Heavy infections can result in defoliation and affected fruit can drop, become distorted, and crack. The fungus overwinters on dead, fallen leaves and produces spores (primary) in the spring that can infect sepals, young leaves, and young fruit during periods of rain. Infection from these primary spores can take place any time after apple growth begins until mid to late June if suitable weather conditions exist. During the summer, a different spore (secondary) is produced by the fungus that is capable of inciting more new infections when splashed onto leaves and fruits by rain.  We had a high scab infection period last Friday and Saturday here at Royal Oak Farm.  It was our first infection period and we applied Dithane and Nova.  Captan is usually our first cover spray for scab, but we still have to do our oil applications and cannot spray captan within 2 weeks of an oil spray.  The nights have not been warm enough yet to apply our oil.

If there is a canker in the location, cut it out and apply a fungicide directly to the affected area.  I usually use apple cider vinegar for dressing the wounds from cankers.  Keep watching your leaves for frog eye leaf spot in case its black rot.  Visit http://www.caes.state.ct.us/FactSheetFiles/PlantPathology/fspp017f.htm and http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2006/21hrt06a5.htm ofr controls and a photo for frog eye leaf spot.  Hope this helps.

Dennis Norton
Royal Oak Farm Orchard
  ----- Original Message ----- 
  From: Thomas Olenio 
  To: 'North American Fruit Explorers' 
  Sent: Monday, April 30, 2007 7:50 AM
  Subject: [NAFEX] Apple question

  Hello All,


  Can anybody tell me what is going on with an apple tree?


  The trunk is about 2" in diameter and part way up the trunk there is a circular, black, sooty spot, 1 ½" in diameter, that appears wet in the center.  It also appears to have run sap at some time in the past.  I have not wiped off the sooty mark yet, but there appears to be no bark damage.


  What would cause this injury?


  Image here;




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