There are black worms crawling all over my pear tree and they seem to be eating the leaves. Do you know what they are and how I can get rid of them?
The black “worms” you're referring to are likely the larvae of pear sawflies, which are often referred to as pear slugs because when you look at them closely, you notice that these tiny beasts have a distinctly slimy appearance familiar to anyone who has ever seen a garden slug.
And that's pretty much all of us.
Pear sawflies usually produce two generations each year, which means two separate sets of larvae get the opportunity to feed on the leaves of your pear, cherry or plum trees for between three and four weeks. Sometimes they even dine on the leaves of cotoneasters.
It’s the topside of the leaves that these slugs are after and when they start munching, the leaves take on a lacy appearance. Eventually only the leaf veins will remain intact.
Pear slugs can range in color from yellow to black and if the ones you're currently seeing are quite dark, that likely means they still have a bit of feeding left to do. When they're finally ready to drop off and pupate in the soil, they'll turn yellow.
This current batch of pear slugs will overwinter in cocoons at the base of your tree until next spring when they'll be transformed into a whole new batch of sawflies that will be ready, willing, and able to torment your pear tree.
Older trees can often withstand a pear slug assault without requiring intervention, but young trees suffer, and occasionally die, when pear slugs are left to their own devices. Older trees have more leaf surface and stronger roots that enable them to withstand the challenge. Young trees need all the leaves they've got to form the strong roots that will eventually help them to survive insect attacks.
Spraying leaves with a sturdy steam of water is a good way to deal with infestations on smaller trees. In cases where the infestation is extensive, you may have to resort to organic pesticides to control the situation. Your local garden centre can advise you on the best products for this use.
Remember that any tree with leaves you can't easily access from the ground or a step ladder is too big for you too effectively spray on your own, so if you have large trees that you're concerned about, you should call in a professional to assess the situation before going any further.
If you have any questions or comments, please send them to me at vanessa@gardenmuse.ca.
Originally published in the Creston Valley Advance on September 23, 2010.
