Spring is well under way. The greens and cole crops are coming in and with them come pests. Swiss chard, spinach and beets can see some of the worst problems from the dreaded leafminers. What were once beautiful dark green leaves are now brown and decaying. I remember the first time I saw this I had no idea what was causing it. As soon as I found out it was on. These leaf miners were not going to destroy my hard work.
Leafminers are maggots. The adults are little flies that law their eggs on the undersides of leaves. The eggs look like itty bitty grains of white rice in small organized clumps of about a half dozen. The maggots burrow into the leaf and feed in between the leaf layers while making tunnels. The mature maggots then fall to the ground to pupate.
Because they live in the actual leaf organic controls are really your only option with controlling them because spraying the leaves will never reach the maggots. Fortunately there are several ways to control them, though prevention is the name of the game.
If you have leaf miners pull off the infested leaves and throw them out, no not compost them. Better yet, if you have chickens give them the leaves. They are more than happy to eat it. If the leaves aren’t infested yet, regularly check the undersides for eggs and simply remove them.
We plant our chard, beets and spinach in the fall rather than the spring. Leafminers are active in the spring so I just bypass the whole leafminer season. Since we’re in a mild winter climate this means we get healthy leaves throughout winter.
Another control that we’ve tried with good success is using row covers. These are a good option for those that can’t overwinter your chard, spinach and beets. Of course this only works if you rotate your crops every year. There’s no use in using row covers if you plant your chard where last year’s flies are going to emerge. A light agribon material over hoops is sufficient for keeping the flies away from your plants. Just remember to weigh down the edges so nothing can go under.
There are several parasites and predators of leafminers but I don’t find these to be consistent enough to save much. You can try using beneficial nematodes to disrupt the pupating stage along with providing habitat for parasitic wasps. But I wouldn’t rely on them as your primary control.