Problems on the empty plot next to mine! Well, the half-empty plot because the front bit is taken by a new fellow who is working hard. But the rear is in mess. There was a large, overgrown damson tree and plenty of tree root penetration in the ground that makes it hard to dig. I thought of taking it over to get the greenhouse that has been left there, but in the end thought the better of it. I don't fancy working from scratch. But I did do some digging on the plot, purely voluntary and out of need, as the place is infected with plum sawfly larvae, and they might get to my damson and plum trees [plum and damson are so closely related that they are susceptible to the same pests]. So needs must!
Sawflies are a group of flies that each take a specific host. They are characterised by the female's having a saw-like ovipositor. With this she cuts into the leaf and deposits her eggs, which then a week later turn to larvae that munch away happily at your leaves. Leaves can be ravaged by this fly. After a while the larvae drop off the tree and burrow into soil, where they dig cells in which to hibernate for the winter. In the cell they become adult and in Spring come out to mate and start the problems over again.
Which plants are affected?
Fruit saw flies include apple, pear [which also affects cherries], plum and gooseberry. There are several different rose sawflies. Willow bean, Solomon's seal, pine, spirea and aquilegia are also affected. Hazel saw fly will affect birch, acer, hornbeam, ash, poplar, willow and some others.
What to do about them.
The best bet is to dig over the soil in Autumn or early Spring when the larva are pupating in their cells. This exposes the larva to cold and to predatory birds. Regular garden maintenance, which involves digging ground once a year will help break up the sawflies' cells.
Cultivation techniques involve picking the sawflies off the plants. Ensure that you look under the leaves, as that is where the larvae prefer to feed, in the shade and the shelter, nice and safe. They hope! Solomon's seal sawfly lays its eggs in the joints where branches break out from the stem, so you can look there. Most gardeners pick off and burn infected leaves. On roses, if leaves are rolled, it might be leaf-rolling sawfly, for which the solution is to pick off and burn the infected leaf.
If you are not organic you can use a contact insecticidebut poisoning the sawflies risks poisoning useful insects. I have never used an insecticide