Caterpillars destroying my Silver Birch

Chocolate

I planted a silver birch in March.

In early July, I saw a caterpillar on one of the leaves of the tree. I looked around and saw another, and another and so on. I pulled about 50 of them off the tree when I realised they were devouring the leaves.

I sprayed the tree but the little nightmares (stronger language is required here) keep coming back and going on a feeding frenzy.

I notice every-so-often that a new branch has been completely stripped of its foliage. I spray again.

Every so often I find a leaf with loads of holes in it. If I look at the underside of the leaf, there are dozens of tiny caterpillars starting off on a new mission. I get rid of the affected leaves thinking I may have killed off the next batch but it just keeps happening.

These creatures work very fast and can strip a branch of its leaves extremely quickly.

At the moment, because the tree is young, we are able to reach the caterpillars/ leaves with baby caterpillars. As the tree grows taller, this will not be possible.

Any advice?

Irish Gardener

Hello Chocolate.

Sounds like the caterpillars you mention are the larvae of the sawfly.
While the tree is younger and small is the time to get on top of these pests.
The larvae create mines or cut the leaves, when the larvae eventually leave the mines they drop to the ground and pupate in the soil.
To prevent the breeding of further and further generations which will become an unreachable problem when the tree grows, you must act in the early years.
You must begin spraying for the first generations of sawflies and larvae to prevent large numbers in any later generations.
The best time for the first spray application is on the the new leaves as they first develop in May.
Areas in leaves where eggs have been laid will develop a grayish shade rather than the normal green of the leaf.
Developing mines will show up as tiny almost see through spots of a lighter green color than the rest of the leaf when leaves are held up to the light.
As soon as either the transparent spots or off color areas appear, a insecticide should be applied thoroughly over the whole tree.
A suitable insecticide will contain the ingredient malathion.
A repeat spray may be necessary 10 to 14 days later if new symptoms appear.

You may have to do this spaying over a few years, but it is better to quell the sawfly population now, otherwise you will be spraying atop a tall ladder in 10 years time.

Remember, read all insecticide labels carefully before applying.

Chocolate

That's them alright, IrishGardener. Thanks. At least I know the name of my enemy.

http://www.dgsgardening.btinternet.co.uk/goosesawfly.htm

They're breaking my heart!

I was hoping it was just going to be a one-off problem this year and that the frost would kill them in the winter.

We'll do our best with the measures you've suggested but I can't imagine trying to control them as the tree gets taller. I think the tree might have to receive an accidental blow of an axe!

One question. The different websites suggest that it's called a gooseberry sawfly and that it attacks gooseberry and some currant bushes. So why is it attacking my silver birch tree? Does it not taste the difference?

Reyman

They usually go for the Gooseberry bushes. If you get them at first sight early in the spring they're easy to control.

They certainly won't bother a bigger tree.

Irish Gardener

Chocolate wrote:

One question. The different websites suggest that it's called a gooseberry sawfly and that it attacks gooseberry and some currant bushes. So why is it attacking my silver birch tree? Does it not taste the difference?

You can have a gooseberry sawfly, geranium sawfly, geum sawfly etc. and so on.
The gooseberry sawfly loves gooseberries but is not adverse to munching on other plants.
I love shepards pie but put a plate of chips down in front of me and I won't say no to it.
Get on top of the sawfly larvae over the next three years, by then your well established tree should not suffer this pest anymore.

Chocolate

Okay, we'll persevere chasing the little darlings.

Thanks for the help.

Chocolate

A year later...they're back! :mad:
They're munching away to their hearts' delight.
I'm so disappointed as the tree was beginning to look quite nice.

They don't seem to have reached the adult stage yet. At the moment I can see loads of them hanging off individual leaves.

I've pulled off as many of the affected leaves as I can.

Irish Gardener wrote:

A suitable insecticide will contain the ingredient malathion.

Irish Gardener, can you recommend any particular brand of spray?

Irish Gardener

Chocolate wrote:

Irish Gardener, can you recommend any particular brand of spray?

Because you will probably be applying the spray to a tree with a bit of height which may cause spray drift, I suggest you look for "LIQUID DERRIS".
Apply this in the evening, whilst wearing rubber gloves, a filter mask and overalls.

Chocolate

Thanks, Irish Gardener. I'll give it a go.