Keeping The Birch Leafminer at Bay

weeping birchFor many years there has been an annual ritual in our neighbourhood, at or around the first week in June, and the whole neighbourhood get’s in a real stink over it!

The “ritual” is the application of an insecticide called dimethoate to the Weeping Birches that grace the yards of many of our neighbours lawns. You see Weeping Birches, in our part of the world get affected every year with a pest called the Birch Leafminer, a little insect that’s invisible to the naked eye, but it grows in the newly grown leaves of Weeping Birch’s and literally sucks the life out of them. It’s also the time we prune the dead wood out with a Cordless Pole Saw.

Green to Dead in Days

birch leaf minerLeft untended these little beggars will decimate a beautiful tree, as about mid summer, you’ll see the leaves becoming dry and brittle, with all signs of greenness gone. By the end of summer 90% of the leaves are dried up and these beautiful birches aren’t so beautiful any more!

The Stink!

As effective as dimethoate is, it has one very unpleasant feature; it stinks. By stink, I mean REALLY stink, a pungent, nose blocking, eyes watering stink, that even from an application to a single tree, can get all your “green” neighbours watching you with disdain.

However, this stuff is so effective, those same “chemical free” neighbours, come mid summer when their trees leaves are wrinkled and dried out, will be stopping by admiring our 30 ft high lush & green tree, with its healthy leaves gently weeping and swaying in the breeze, and hinting at getting a little of “that stuff” for their tree.

The Two Application Methods

The Paint On method
When the tree is younger, the preferred method is to just paint a strip around the trunk of the tree, directly on the bark. You calculate how wide to make the strip by the height of the tree, so a small tree will have a very thin strip, then as the tree gets taller, the strip should be wider.

And when the tree gets a littler older

The Soil Drench method
When the tree gets larger, probably over 15 – 20 ft., then the better method is to soil drench the dimethoate in. This is pretty easy to do, you just determine how much to apply by a calculation from the tree’s height, then make a series of holes in the ground, directly under the “drip line”, or outer edge, of the branches. I just use a large screwdriver to make holes about 4″ deep, then simply pour the dimethoate into the holes, then water the area profusely.

Then you go and visit some friends a few miles away, as the “aroma” will be not too pleasant for a couple of hours!

How it works

Dimethoate is a “systemic” insecticide, meaning that it will be taken in by the roots, or the bark, and enter the sap of the tree. If you apply it at the first sign of leafing out in the spring, the tree’s sap is actively moving up from the soil right to the very tips of the highest branches and all the newly emerging leaves. The insecticide then is ingested by the Birch Leafminers and selectively kills them allowing the tree leaves to remain lush & green.

Nothing else is affected, no other “good” bugs are harmed and the tree flourishes.

Apart from a stink (that only lasts a few hours) it’s a thing of beauty!

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