Yes, we’re getting to that time of year when all my friends and neighbors greet me with crinkled citrus leaves.
What’s wrong with my citrus?, they wanna know. And if you’ve got a citrus, I guarantee you’ll be horrified by the same sight: Brand new citrus leaves that are still bright green, but look like a piece of crumpled paper, folded, distorted and ready for the waste can.
You’re looking at the craftsmanship of the citrus leaf miner. Take a closer look, and you’ll actually see the leaf miner’s interesting scrollwork, as he burrows around inside the cuticle of the leaf.
But before you go all postal on the citrus leaf miner and shoot yourself in the foot, let me try to reassure you: As bad as the damage looks, it’s usually of little consequence to the citrus plant.
First off, the leaf is still green and hanging on the plant, and that means it’s still absorbing sunlight, and that’s what’s important to the plant’s health. Sure, all that digging around by the leaf miner reduces the amount of sunlight a leaf can absorb, but not by much. And the leaf miner only attacks the youngest and often the smallest leaves that appear in late summer, so most of the leaves on your citrus are not bothered at all.
There’s little or no reason to worry about the citrus miner actually reducing the yield of your citrus. And spraying has limited impact, since the leaf miner is already inside the leaf, where the caterpillar is out of the reach of any foliar chemical spray. Still, there’s no denying it LOOKS bad, and it will drive some of your to distraction. And in some unusual cases — if trees are very young and very unhealthy, or if they’ve been stripped by a hurricane — the citrus leaf miner can delay recuperation.
Is there any hope we’ll learn to control the leaf miner?
Well, sort of. Several predators of the leaf miner has been identified or introduced in Florida, and they are presumably working their way here. They’re not likely to eliminate the leaf miner, but they may well reduce the numbers.
Meanwhile, you should make sure you’re not actually promoting damage by the leaf miner. In our climate, the citrus leaf miner almost never does damage in spring. It only becomes a problem on the late summer and early fall flush of soft, new leaves. Older leaves that have already hardened off are not bothered by the leaf miner at all. So DON’T fertilize your tree heavily in the second half of the year, or you’ll actually encourage more soft leaves and more damage by the citrus leaf miner.
On very young citrus, the best protection is to make sure they’ve grown well and put on plenty of new leaves in spring. If they have, the citrus leaf miner isn’t going to do much. You may also be able to reduce damage somewhat if you spray horticultural oil on the tops and bottoms of the leaves on a fairly frequent basis from late July on. Horticultural oil is not toxic to people, but deadly to many insects. But be very careful about resorting to heavy chemicals, since you’re going to be eating the fruit of this tree.
Garden writer and MBG Executive Director Bill Finch is happy to answer your gardening questions.