>> The copper was recommended by the nursery people. My trees have been getting brown disease that … >>
Copper, oil, in fact, many sprays if sprayed in the fall to mid spring will kill a lot of beneficial insect pupa in the trees like praying mantis, ladybug, possibly predatory beetle pupa in the mulch around the tree, and certainly other insect pupa too. The pupa need to over-winter and hatch in the spring. Anything that suffocates them (oil), or any toxin like copper will kill them. In addition copper is a phototoxin that will kill a lot of the beneficial micro flora.
In my cynical opinion, the main desire of a nursery section is to sell stuff. If they sell – or give directions to spray things that kill beneficial and predatory insects — that will only benefit the pocketbook of the nursery later on. They get to sell more garbage down the road. I’m not saying it’s deliberate either it’s just what they have been taught…. “4 out of 5 doctors recommend Camel cigarettes.”
If the symptoms you see are most obvious in summer I would spray a light compost tea on it _in summer_.
Oh, BTW, are the trees on a dwarfing rootstock? Here is a bit of a post on my blog: Starts about halfway down this post. — http://www.puravidaaquatic.com/wordpress/tanglefoot-stuff/ ….
So the agrocompanies graft onto a rootstock that cripples a tree and then are pleasantly surprised that the tree gets sick more often. Well the pests have just become more robust right? Can’t be that the tree they sold is sickly– exactly why is it a dwarf?
And horrors for the agrochemical companies, the homeowner has to use more pesticides to keep the the crippled tree healthy (darn!). Well, as healthy as possible with a dwarfing rootstock.
I used to smirk a little about compost tea, but it really does help rejuvenate the normal bioflora of the tree. They’ve finally figured out that the microbes on us humans outnumber our own cells 40 to 1 and I would bet that ratio is approximately the same for a tree. We know so little about biology. So we poison everything we don’t know anything about.