Last week I visited my friend to get some crabapples for my crabapple jam. While I was there we wandered around her makeshift orchard, admiring the various fruit trees she had planted.

When we got to her pear tree she pointed out this strange, black sludgy thing that was on the leaves of her pear tree. She had no idea what it was, and I had never seen it either. We both hoped it wasn’t anything particularly bad, and moved on to discuss some of her other plans.

Today I was out in the garden picking some apricots and admiring the fact that my pear trees still have pears (the immature fruit mysteriously disappeared last year).

Pears still growing!

As I admired the fact that I still had pears I noticed that I, too, had these strange, black sludgy things on the leaves of my pear trees!

My first thought was “GROSS!” and my second was “what on earth is this thing?”.

A quick google search tells me that my pear trees are currently infected by a fairly common garden pest – the pear and cherry slug.

Apparently the slug is actually a caterpillar and is the larval stage of a sawfly (closely related to a wasp, though it is unable to sting). The caterpillar (and wasp) aren’t dangerous, and the main damage they cause are the skeletonisation of leaves. Ruin enough leaves and the plant won’t grow, though, so this is particularly problematic for new and establishing trees. Interestingly, while my newer pear tree has a fair few of these caterpillars feasting on it, my older pear tree is basically untouched…

These pests are fairly easy to control without resorting to insecticide (though you can do that if you want). The three main ways of dealing with them seem to be as follows:

1. Squishing the bugs by hand (this is the approach I took, though I’m slightly squeamish about squishing the bugs so where leaves were fairly ruined and/or had more than one caterpillar, I removed the leaf from the tree).
2. Hosing the tree down with a high pressure hose. Apparently the caterpillars are weaklings and a sharp blast of water is enough to have them fall to the ground where they stay.
3. Drying the caterpillars out by covering them with woodash or another form of dust.

All of these approaches will need to be repeated frequently to ensure that the pests remain under control (though if you only have a mild infestation you could also choose to leave them on the tree where they won’t do too much damage).

They also overwinter as a pupae in the soil at the base of the pear/cherry trees, so some people have had success in controlling these pests by letting their hens scratch up this ground and destroy the pupae. I wonder if Nick will find this a compelling reason to get hens (so far he is refusing)…

Have you encountered any garden pests? How do you deal with them?