[NAFEX] Help identifying apple disease

dmnorton at royaloakfarmorchard.com dmnorton at royaloakfarmorchard.com
Sun Jun 24 20:36:18 EDT 2007

Mark, here is some info I have on burr knots:

These notes are from Dr. Turner Sutton, NCSU Apple Specialist: 

Burr knot is where adventitious roots are trying to develop. A few apple varieties (especially early "June" apples) appear particularly prone to the development of the burr knots, as does some rootstocks such as MM111, Mark and M26. No one knows exactly what causes it although it has been associated with wooly aphid feeding injury. Control wooly aphid so burr knots are not allowed to form.  There is no control for burr knots. A product known as Gallex can be painted on burr knots and will result in at least some of them forming callus and "healing". Often various organisms (i.e. dogwood borers) get in the burr knots predisposing the tree to secondary wood rot fungi that can girdle branches, or even the trunk, weakening the tree. 

The tree is not likely to be productive in the future and should be removed or at least remove the affected scaffolds of branches. also, see my other post on dogwood borer.

Hope this helps! 

Dennis Norton
Royal Oak Farm Orchard
  ----- Original Message ----- 
  From: Lon J. Rombough 
  To: North American Fruit Explorers 
  Sent: Saturday, June 23, 2007 11:05 PM
  Subject: Re: [NAFEX] Help identifying apple disease

  Burr knot of apples. Related to crown gall. Certain rootstocks, and apple varieties, are more susceptible to the condition than others. Some sources say the tree is non productive with them, but others say they can be controlled with Gallex, a treatment for crown gall.
  I've seen apples that had the knots but were apparently healthy and productive, so your neighbors have to decide if the problem is bad enough to remove the tree.
  -Lon Rombough
  Grapes, writing, consulting, my book, The Grape Grower, at http://www.bunchgrapes.com Winner of the Garden Writers Association "Best Talent in Writing" award for 2003. 
  For even more grape lessons, go to http://www.grapeschool.com
  For growing supplies and more; http://www.grapegrowersolutions.com

  On Jun 23, 2007, at 8:59 PM, Mark & Helen Angermayer wrote:

  One of my neighbors has a couple of diseased apple trees that have severe cankers all over.  They've had these cankers for many years, but the trees continue to survive.  Both trees produce fruit.  I have never seen the typical fireblight symptoms of black shepherd crook twigs, but there are small mummified black fruits left over from last season on at least one of the trees.  Additionally, one of the trees shows symptoms of CAR on the foliage, but the other shows no CAR.  As far as I can tell there doesn't seem to be any major scab going on.  Except for the CAR on the one tree, the leaves look fairly clean.  Any ideas what may be producing these ugly cankers?  Oh, by the way, there is a third apple tree right in the middle of the diseased ones that doesn't have any cankers.
  Here are some photos:
  Zone 5 Kansas
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