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Monday, February 11, 2013

Chums and Shothole Fungus

Q. I recently saw your youtube video regarding shot hole fungus and found it very helpful.  But I was wondering if you could provide some added insights.

Q. I live in zone 5B (Montreal, Quebec, Canada) and I planted a "chum" (cherry plum cross) tree a month ago in my backyard.  I believe it is stricken with shot hole fungus (see following video: http://www.youtube.com/watch?v=hs6jPVWP0-w&feature=youtu.be). As you said in your video I will only apply a Bordeaux Powder after the leaves fall in the autumn but I was wondering if there was anything that you recommended that I could do now to prevent the spread of the disease throughout my tree and prevent the fungus from spreading to my neighbouring fruit trees/plants (asian pear, european pear, raspberry, grapes, strawberries)? 

Should I remove and burn all foliage that is stricken with the fungus? No it's a mix of cherry and plum (prunus besseyi x prunus salicina). Perhaps it is a physiological disorder then.  I can remember we used to have a large tree that was planted in the same spot as my chum tree and it always prematurely lost it's leaves come late summer or early fall. Other trees all had their leaves but it lost it's leaves well before the other trees. In the end we removed the tree.  But I'm wondering if perhaps it is something that is in the soil.  I know the soil is quite tough in our backyard and is more of a clay soil.  Not sure if that provides any valuable insights.

A. You are out of my climate zone (and comfort zone) so I sent an email to Maxwell Norton, Fruit Advisor at University of California Extension in Merced, California and Tom Spellman at Dave Wilson wholesale fruit nursery for thier comments.
Most of what I understand is that plums seldom if ever get shothole disease. They get holes in their leaves but my understanding is this is physiological and not pathological in nature. Holes from shothole fungus should be rimmed with a purple or brown margin. When they occur physiologically then are not rimmed with any color but may have a crispy brown edge rather than any color.

Response From Maxwell:
Shot hole disease is rare on cherry and plum.  If it is warm enough and wet enough anything is possible. The non-infectious shot hole disorder on plum develops in late spring, beginning on older leaves and progressing out the shoot.  Small translucent spots turn brown and fall out. There is no treatment.
Sometime bacterial blast can cause holes on stone fruit.  Cold, wet conditions may favor it.

Prunus necrotic ring spot virus can leave cherry leaves tattered.  No treatment for that either.

From Tom Spellman:
Bob, Sprite and Delight (cherry plums) are superior selections of Myroblyn Plum that seem to fruit in all climates. The fruit is about the size of a quarter or slightly larger. They have fruited successfully in all zones from 3 to 9 and the fruit ripens July through September depending on how far north you are. They have a balance just slightly toward the acid side and are quite flavorful when tree ripe. They are interfruitful and will also pollinate with other Japanese Plums and Pluots. We offer them as single budded trees and also as a two in one with both varieties grafted to one  Citation rootstock.

The new release for the 2013 season is a true Plum X Cherry cross named "Pluerry - Sweet Treat". Don't yet have much information about zone adaptability but I'm hopeful its low chill as the fruit is delicious. In the central valley it fruits from mid July through August. Requires another Japanese Plum or Pluot for cross pollinization. I strongly feel Burgundy Plum and Flavor Grenade Pluot will work well.  We are releasing it as 500 chill hours recommended. However with the Plum parentage it could be much less. This is a great variety for experimentation.  I have recently planted two to my orchard and have it in a test plot in south Orange county.

Bob, I will get you a couple for you to try in the UNCE orchard in North Las Vegas.

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