Well, it officially tomorrow. Tree no feel so good.
First time out with Mrs Tree in nearly a year. 0 for 3 against #4 ranked Canadian 8 ball player although I managed to get within the 8ball once (tough when you're seeing double)
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As for leaf miner on birch, don't worry about it. You can't spray because they live within the leafs, and the membranes will prevent the insecticide from killing the little buggers.
A systemic insecticide can be somewhat effective as the tree ingests it through the root system (think an imunization shot).
Otherwise, do everything you can to boost the tree's health. For the most part, a heathly tree is capable of either fending off or weathering anything that gets thrown at it. A tree with a compamised system will be vulnerable to attacks. Particularly birch. They are highly prone to aphid infestations, minors and bronze birch borers (they take out the tops).
Water the absolute sh*t out of it! Birch love tons and tons of water. However they love good drainage too. Weird. Anyway, water, water, water. Go to a garden center and get a systemic insecticid and follow the instructions. Water, water, water. It'll work. Just before the frost sets in, water, water, water! If you can get the root system locked up in a block of ice, its a really good thing. It keeps is dormant for the entire winter, and it is a bit slower coming out in the spring, which is good because it keeps the tree from facing any of spring's litte tricks like late snows and late frosts.
Other than that, the miners are usually minor.
Most bugs exist in a sysmbiotic state with their hosts. If they killed their tree in short order, they too would die along with any eggs they've laid. Kindda pointless from an evolutionary perspective, eh?
Good luck, and I hope that this is more helpful than my last post. I'm going back to bed, my head hurts!
Tree