Question: I have two 2-year-old Miss Kim lilac bushes which have done fine until about a month ago. Since then, the leaves have developed brown edges and are slightly folding closed. I cannot tell the cause and have sprayed twice -- once with Safer fungicide and once with Safer insecticide, but there has been no change. The old established lilac next to them has not been affected. Can you tell me what's wrong with the Miss Kim's?
can play host to leafminers (which tunnel around between the upper and lower leaf surfaces), and to bacterial leaf blight. Both of these problems will make leaf tips turn brown and curl up.
Leafminers are the larvae of an adult fly. She makes a little slit in the surface of a leaf and lays her eggs. The eggs hatch into little worms who happily feed on leaf tissue. Since they're between the upper and lower leaf surfaces, they are immune to insecticide applications. When they're mature enough they make an exit hole in the leaf and spin a thin web to lower themselves down to the ground. Here's where they pupate, emerging the following spring.
Insecticides are not very effective against these pests. Your best course of action is to pick off any leaves with miner tunnels and squish them to kill the larvae.
Lilac leaf blight is a common problem, especially if plants are stressed. To avoid, maintain adequate spacing between plants, prune out and dispose of affected tissues as soon as you seed them, and don't overfertilize.
The disease can overwinter, and can be resistant to copper based fungicides. Spray with Bordeaux (lime-sulfur) after leaf fall and again in the early spring. Be sure to rake and remove all fallen leaves from the garden.
Hope your Miss Kim regains her health!
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