In my last post, I put up a challenge that was accepted by two worthy gardeners. Readers were asked to figure out this puzzle:
What is this plant and what happened to it?
Nancy hit it on the head with columbine and leaf-miner damage.
Coming in second, Marcia makes a good case for gingko leaves, noting that many gingkoes have been planted in New York City (I have stepped on their very smelly fruits on city sidewalks).
I see leaf mining every year in columbine plants at the Clinton Community Garden. The only other plants in the garden that I’ve seen with this kind of tunneling are hollyhocks. The columbines seem strangely unperturbed by this summer-long attack on their leaves, but the hollyhocks that are invaded are often decimated. Could it be partly because columbine plants have so many leaves? Hollyhocks put out fewer, though much bigger, leaves.
The creature doing the mining is something I haven’t really paid much attention to. By the time I notice what’s happened, the adult insect has emerged and moved on. Now I know that a kind of fly is responsible for columbine damage, but there are other types of flies, moths, beetles, and wasps that also attack specific plants this way. It’s pretty ingenious on the part of the insect: She injects her eggs inside the leaf. When they hatch, they begin eating their way through, protected above and below by leaf tissue, and emerging as an adult at the end of the tunnel. You can chart the growth of the insect by the widening of the tunnel as it reaches the end of the leaf. Columbines are known for surviving this parasitism quite well and are used as traps to protect more vulnerable plants (in greenhouses, for instance). Another reason to love my columbines.
Some side notes to leaf mining: To minimize infestation, don’t compost the damaged leaves. Hairy-leaved plants discourage leaf miners.