Everything You Really Need to Know to Organically Control Birch Leaf Miner


Birch leaf miner is a particularly noxious pest of birch trees and more importantly has spawned some even more noxious chemical controls.

To Begin

it is important to keep your birch trees healthy and actively growing.

This means feeding them with compost (a quarter inch spread under the leaf canopy every spring or fall) and making sure they don’t suffer drought damage.

So feed and water are important to reduce the stress on this plant (as it is with every plant).

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Birch tree leaves

Understand that a tree under stress will be more attractive to pests. So the most important, least-costly and most-effective first step is to feed and water.

Also understand that the birch leaf miner will not usually kill a healthy tree even if it totally defoliates it.


It helps to understand the life cycle of this insect


The life cycle is important because it is an interesting and very protective one. The pest is a species of sawfly that overwinters in the ground as a pupa. The adult fly hatches in the spring and immediately flies to the emerging leaves, makes a slit in a leaf and lays the eggs. The adults then die after a very brief lifespan.

The egg hatches and an immature worm or birch leaf miner starts eating away between the layers of the leaf where it is protected from predators and our typical spray methods of control. When it is ready to develop further, the miner drops to the ground and burrows into the soil and makes a pupa. There can be several generations of birch leaf miner each year with the last one staying in the ground to overwinter and start the process again.

So how can we control this pest?


A contact spray


A spray such as soap will kill the adult sawfly but your timing has to be perfect to get it - just as the leaves are unfolding. The difficulty with these sprays is that birch trees can be quite tall and getting a complete coverage involves spraying almost everything within a half mile with the spray drift.

A contact spray will not penetrate the leaf so the miner (larval form) is quite happily eating away.

Contact sprays will not penetrate the ground to kill off the pupa.

Horticultural oil


Horticultural oil has been shown to be effective against birch leaf miner. A spray as soon as the leaves start unfurling and weekly until June will provide relief on smaller trees. Hort oil will stay on the leaves and will have some residual action. Repeated spraying are necessary as timing the hatch is critical.

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Neem oil


This oil apparently acts as a deterrent to birch leaf miner so this should be considered.

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Predator nematodes


These are the good guys. And the same species that are used against lawn grubs are listed for the control of the burrowing miner and larva. Apply as per the instructions on the label and make doubly sure you water these small creatures into the soil after you apply them.

Spinosad


This is a new form of insecticide and you might want to investigate this chemical for control. It is being used in IPM programs now. The jury is out on its effectiveness or ultimate ecological impact.

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Rotenone


Rotenone is registered for use with sawflies but the problem with Rotenone is that it is very short-lived (24 hours) and you have to ensure the fly is flying or around before you can kill it. You have to get the adult form of the birch leaf miner with this material to be effective. Again, this is a very potent botanic insecticide and full breathing masks should be worn if dusting or spraying with this material.

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Cygon 2E is Not Recommended


This the chemical of choice and most often sold but this is one of the most toxic chemicals used in the agriculture industry.

I would not recommend this in any shape or form.

The interesting factoid about this chemical is that it has probably killed more birches than the miner. You see, if you apply this using the label directions and paint it on the trunk for two years in a row (or more) then you may wind up killing the cells right under the bark and the tree will die. The birch leaf miner gets the blame but the Cygon did the deed.

Never, ever spray Cygon with a sprayer – this is acutely dangerous material.

Doug's Best Organic Option


Use predator nematodes to get basic control. You'll likely have some problems but not at a level of tree destruction.

If the problem becomes worse, apply more nematodes and spray with the horticultural oil or neem at the appropriate time



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