By mid June in Edmonton most woody plants are rapidly growing new shoots and leaves. This new growth is exciting to watch, but it also creates an opportunity for many unwelcome visitors that take advantage of the young tender growth. One that we’ve noticed for a few years now in our urban orchard is the apple leave curling midge.
One of the signs of the apple leaf curling midge is, unsurprisingly – curled leaves. The affected leaves are usually near the end of growing shoots and are often discoloured. There are other pests like leaf rollers that also cause rolled apple leaves. However, if leaf rollers are responsible you are less likely to see the discolouration, and there are often silk thread/webbing around the affected areas.
There isn’t a lot of advice out there for the home gardener dealing with the leaf curling midge. It usually doesn’t cause too much damage, especially on larger established trees. But – if you are like us and are working with some younger trees, the damage can be enough to impact the tree’s growth. Apple Leaf Curling Midge probably isn’t the biggest threat to your apple trees, but if you start to see a lot of curling leaves like I have, it might be worth trying to manage it.
The midge is a small flying insect that lays eggs on developing leaves, which eventually hatch into small larvae that eat the leaves as they develop, leading to the curled, deformed, discoloured leaves. The larvae usually drop to the ground, build cocoons just below the soil surface, and then emerge to fly back up an lay more eggs. I checked inside the damaged leaves, and sure enough there were the larvae!
In an urban neighbourhood with lots of apple trees there will always be more pests around the corner. We can’t control what happens in every yard, so trying to completely eliminate any one pest is unlikely to succeed. What we do instead is focus on minimizing the damage and reducing the number of pests in future generations. In this case that means doing a bit of summer pruning.
The badly damaged leaves aren’t going to do much good for the tree. Leaves are supposed to catch sunlight and a rolled up leaf will not do that very well. These larvae in the leaves will also just become more midges. More midges to lay more eggs and start the cycle all over again. I’m going to get rid of these damaged areas entirely. You may be able to pinch off individual leaves with your finger, but depending on how much of the tree is impacted, pruning tools will be helpful.
*Remember to give any tools a quick alcohol wipe in between trees to minimize the risk of spreading diseases around.*
Because of where they lay their eggs, midges are most likely to impact multiple leaves towards the end of a growing shoot/branch. I like to cut back the shoots down far enough so that all affected leaves are removed. Cutting off the growing tip of the shoot will also remove any eggs that might exist the budding leaves. Seeing that these leaves do have larvae in them, I dropped everything I cut off directly into a bucket of soapy water so that the larvae never has a chance to reach the ground and continue their cycle.
There will probably be midges on the trees again, potentially even in the same summer. The midges can sometimes complete a few lifecycles in one season. Catching these ones early enough will hopefully mean less damage in the future and give the trees a chance to put on some new healthy growth for the rest of the summer.