12th September 2016
I heard on the radio this week that we can expect to see a greater number of crane flies than normal. The reason seems to be due to climate change and the wet autumn last year.
The European crane fly or to give it its proper name Tipula paludosa, emerges at this time of year. The crane fly is the short-lived adult stage, which emerge to mate and for the females to lay eggs. Typically they live for around 10 to 15 days. These adults do no harm and in fact they don’t even feed during this final part of their life cycle.
However, the larvae known as leather jackets can cause considerable damage to lawns and young plants by feeding on the roots. The larvae emerge from their eggs within 24 hours or so of being laid and then bury themselves into the top couple of centimeters of soil. They prefer moist soil and generally do not do well in dry soil at all. Evidence of their presence on lawns can be seen in early spring. An affected lawn will develop yellow/brown patches as a consequence of the grass roots being partially or completely eaten.
If you see your lawn turning yellow/brown like this (see left) in February to April then it is possible there are leather jackets. A way to confirm this is to soak the suspected area with water and then place some black plastic over the wet ground, to block out the light. The next day lift the plastic to see if there are any leather jackets, which will be visible on top of the ground.
There are no chemical controls for treating leather jackets which are available to the home gardener. However, it is possible to use a biological control that is available from Nemasys. Nemasys supply nematodes or microscopic worms which invade and kill the leather jacket. They are harmless to other wildlife and easily applied via a watering can. As these are live micro-organisms it is important they are used straight away although they can be stored in a fridge for a few days if required. The best time to apply nematodes is when the crane flies are around. The best procedure is to water the lawn thoroughly then with a watering can, water in the nematodes. You need to keep the ground moist for the next week or so after adding the nematodes as they prefer a moist environment and will die if the ground dries out.
If you find you do have a major problem with leather jackets then another option is to look at the lawn environment. A lawn which is moist for most of the year represents the ideal soil type for leather jackets and consequently they will thrive. However, Leather jackets do not do so well in a well-drained soil as they can dry out quickly and die Therefore, a way to help control a serious leather jacket problem is to improve the lawn’s drainage. This is best achieved by hollow-tinning a lawn first then sweeping in some horticultural sharp sand into the holes. As the soil becomes more free draining you should see the number of crane flies reduce noticeably.