plum tree advice - to spray or not...

All,
I'm new to this gardening game, but bear with me. We have a plum tree that's not too well. According to the arborists who have come to have a look, we have black knot, aphids and something that does leaf cutting (ants?). Now, both people who came out recommended pruning out the black knot, which is okay with me. However, person A said that they would use an insecticide and a fungicide to get rid of the aphid and leaf cutter problem and then fertilise the tree, whereas person B said that they would just fertilise and would not spray.
Now, my question is this, will fertilising alone invigorate the tree enough so that it'll recover next year? i.e. come back with a vengence. Or is it better to spray the tree now and then spray again and again each year? Incidentally, the plum tree is (on their estimates) approx 30 yrs old, so it must be relatively hardy? and we are apparently in Zone 43 in Canada, if that helps?
I know it's hard to give advice without seeing the tree, but I guess i'm really asking whether or not the aphid and leaf cutter problem will always be there and one should just fertilise and let the tree look after itself!
cheers
col
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On 24 Jun 2005 07:04:41 -0700, snipped-for-privacy@hotmail.com wrote:

It may already be too late.
Cut at least 6-inches below all of the ugly black growths and then see what is left. Be sure to sterilize any cutting tools after you use them on this tree.
I would then apply an appropriate insecticide to eliminate the aphids and leaf cutter to give the tree the best possible chance of survival.
Fertilizing may or may not be helpful. One of the problems that you will have is that the pruning will stimulate rapid new growth that will probably not have time to harden off before winter. I know that sounds odd as it is just barely summer but most of this year's growth has already occurred and anything that starts now may not haveenough time. Much depends upon the fall weather. Fertilizing may make the winter kill problem worse - I would not fertilize at this time but that is just a gut feel.
Nothing that you described calls for a fungicide. Perhaps "person A" spotted a fungal problem that you have not noticed?
JMHO
John
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