I’m a new fan of Swiss chard, after having grown it for the first time last year. Its edible Technicolor stalks – yellow, orange, red, magenta – alone would make this plant interesting. It keeps growing the more you cut. Add the qualities of leaves that can be eaten raw in salads or cooked, a hardiness that carries it through the winter, and a strong work ethic that keeps it producing even in summer heat when its taste-mate spinach has long ago bolted -- and you’ve got one versatile veggie.
Sounds too good to be true. Sigh.
Last summer when my chard plants were marked by tan, dried-up leaves, I chalked it up to extreme hot and dry July conditions. Everything else was wilted, too, and I thought water stress was the natural cause.
Chard is a biennial, meaning it grows one season and comes back the second, when it goes to seed. My chard plants sailed through winter, bursting forth with new greens early in the spring.
Yet I’ve already noticed the same sort of damage this year that occurred last, and I knew drought couldn’t be the cause so early in the game.
I more closely examined these leaves, practically recoiling upon discovering worms burrowing INSIDE the leaves, making something two-ply that I thought was just one.
I learned that leaf miners are the culprit. These maggots are the larvae of a fly that lays its eggs on the leaf. When the eggs hatch, the maggots go inside the leaves, leaving ugly black-dotted blotches in their wake. Eventually the leaves turn brown. The maggots I found ranged in size from 1/8- to 1/3-inch. After burrowing for a time the maggots drop to the ground, pupate and become another generation of egg layers in fly form.
Beets and spinach are also susceptible to leaf miners. For a leaf crop like spinach, they can be especially devastating.
By the time you see leaf damage, this downward cycle is well underway, and quite difficult to interrupt. These leaf miners know what they’re doing! As maggots they’re safely cocooned inside the leaf tissue, where two standard organic methods – handpicking them off or spraying with insecticidal soap – are thoroughly ineffective.
So what to do? My cursory research on this pest pointed to trying to kill the eggs by using Spinosad, a relatively new product, which is registered with organic growers. The eggs appear on the underside of the leaves. Long and white, they looked to me like tiny grains of rice neatly arranged in the same direction.
Another approach is to try to kill the pupae form in the soil, by adding beneficial nematodes. Using floating row covers is also said to help prevent the fly’s access in the first place. I’d be interested to know if any of you have tried these methods.
Realizing that every damaged leaf houses bugs seeking many great-grandkids, I thought it best to . . . well, nip this in the bud. I started to remove every single leaf with splotches. I cut them off with the stalk, which I separated and saved to take to the kitchen. Rather than composting these leaves, I chose to put them in the trash, because I don’t know if the leaf miners would survive the composting process. If you have chickens, feeding your brood is a great way to destroy leaf miners and their pads!
I also checked the seemingly pristine leaves for eggs. I found a few egg clusters on the top side of leaves, but for the most part the eggs were all underneath. I removed these leaves too, but set them aside for eating, since I can easily rinse or cut off the small sections with eggs.
This picture shows a plant before and after I removed damaged leaves. It was such a drastic transformation, that for the other plants I decided to save myself some time and just cut them down to about three inches off the ground. One of chard’s qualities is it will form new leaves even after such a brutal harvest.
Remember, too, that unlike spinach, chard’s stalks mean that this extreme defoliation was not a total loss. As far as I could tell the stalks were not affected by leaf miners at all. Yet from now on I’ll plant spinach and chard far from each other, so an infestation of one won’t be as likely to affect the other.
I will be more vigilant in my chard patch to remove any leaves with eggs or damage right away. I also hope that through more frequent harvest of smaller leaves there won’t be as many chances (i.e. places) for flies to take roost. If the problem persists on a large scale, however, I may dig up and destroy my plants altogether to try to get rid of these pests, and then plant chard in a new location in my garden this fall. (I saw ants tugging away what looked to me like the maggots-turned-pupae; maybe I could enlist them to help?) I’m not sure how cooler temperatures affect the leaf miner, but I will not let infested plants carry over into winter again, as I unknowingly did this time around.