Q. Several years ago I purchased a Raywood Ash and I have been pruning off infected branches at the beginning of each season. Last week someone had a nursery suggested I apply a systemic containing imidacloprid and clothianidin as active ingredients to try to get some control. Do you know what the problem is?
|Cicada damage to small limbs on sweet acacia|
A. The problem you are seeing is most likely cicada damage from egg laying that is now healing. The female cuts a slit parallel along the top of the stem parallel to the branch with her ovipositor (egg laying machinery). The female deposits her flattened oval eggs, about an eighth of an inch long, stacked up against each other along that slit in a nice row.
|Cicada (probably apache cicada) on the limb of a sweet acacia in late June|
If you look at the old twig damage closely, the slit looks like tiny teeth on a saw and that slit is healing nicely. When the eggs hatch a few weeks later, the babies fall to the ground and take into the soil where they feed on tree roots.
The insecticide applied as a soil drench might work because it is systemic. Another option is to apply a soil insecticide drench intended for killing grubs in the soil or eliminating the cicadas on the tree as you see them and before they have a chance to cut a slit and lay their eggs.
Continue to cut off the branches if you want if they are unsightly to you, but the tree will heal fast if it is kept healthy.