Two questions.....

[Jumper]

I really gave my own crabapple a thorough pruning this past spring and it is the only one in the entire subdivsion that is healthy....all the rest have fireblight and are missing about 2/3rds of their foliage. Is this robustness due to the fact that the tree got a prune job and thus air circulated in the crown, or was it just luck of the draw that it did not get diseased?

Secondly my otherwise healthy cedar hedge has a few brown/dead branches, about <5%. Otherwise looks OK...is this a result of the driest summer ever or should I be loking at something else?

Tanx

 

[John Paul Sanborn]

1. probably due to cultivars and maybe you water it a little. Some varieties of crab ar more disease resistant. Air movment can reduce the incidence of scab infection , but it is just one of a number of factors. Are you mulching too?

2. it is normal to have some dieback in evergreen hedges. Any number of things can cuase it, insects, squirrels...

 

[Jumper]

Originally posted by John Paul Sanborn
1. probably due to cultivars and maybe you water it a little. Some varieties of crab ar more disease resistant. Air movment can reduce the incidence of scab infection , but it is just one of a number of factors. Are you mulching too?

It was vertically mulched this spring with some fertilzer in the bottom of the hole. I think every crab here is the same as they were installed when the homes were new as part of the City's greening program. I did not water it at all as our water bills were hiked almost 200% this past year.

]

 

[tshanefreeman]

As I'm sure you know, the bacteria causing Fireblight are transported via several vectors, one being the wind. Therefore, increased air circulation should make a difference in the probability of infection. (Keeping in mind that there has been no personal research on my end.)

This summer many Mountain Ashes in my area were devistated by Fireblight. Complete blocks showed the damage. Yet, right in the center of it all, literally feet between each other, would be a healthy tree. Not a single branch illustrating dieback. Absolutely no visible signs or symptoms. Why?

* Was this due to a new resistent variety?

* Did the air move faster by this tree, thus hindering the bacteria's ability to infect the blossoms?

* Has the homeowner taken care of his/her tree in a different manor, therefore accounting for the difference in resistence?

* Or was this due to chance?

What ever the cause, it is a mystery to me, but I'm sure that the answer is just between the lines?

 

[Nickrosis]

.....or

*Does the tree possess the vigor (genetic strength) to resist attack?

 

[John Paul Sanborn]

my bet is more on vitality (
health related strength) of the individual plant and site locations.

I've heard that Sorbus is like some betula in that they need cool root zones, sunny turf can stress the tree and make it suseptable to pests.

 

[tshanefreeman]

Yes, I too have read and learned that Sorbus sp. prefer and thrive in a two-fold growing habitat, just like the unrelated Betula sp. Their root systems prefer and thus thrive in shady conditions, but their tops prefer full sun to optimize photosynthesis. Organic mulches are a great way of controlling the temperature fluxuations from day to night.

 

[Nickrosis]

My vigor concept is thrown out if they are all cuttings from one tree, grafted to root stock. Nevertheless, it seems the environmental factors are the same or inconsequential for all the trees. Therefore, it leaves the vertical mulching, pruning, and genetics as the most important variables.

Nickrosis

 

[John Paul Sanborn]

All you need is a little swale, or slope with a northerly face too it. Anything to reduce the amount of exposer to sunlight. A bush or tree or lawn ornament, or mostly eastern face....