Leaf Miners on Vegetables
If you have ever grown columbine you probably recognize the insect damage on the leaf above. Leaf miners is the common name for the larval stage of several different types of insects including moths, flies, beetles and sawflies. The term “leaf miner” is actually referring to the tunneling damage caused by those insects between the layers of the leaf surface. Many of those insects will feed their entire larval period within the leaf and some will pupate inside the leaf before emerging as an adult. There are usually two generations in our area with the second generation overwintering as pupa in the ground to emerge as adults in the spring.
In Kansas the most common leaf mining insect of vegetables are a type of fly and the maggot is what is causing the damage in the leaf. In tomatoes and ornamental plants, the damage they cause usually doesn’t harm the plant and only makes the leaf look bad. When it comes to plants that we eat the leaves from however the damage isn’t just superficial, it can make the leaf inedible. While the tunnels and the insects themselves are not a cause to stop eating the leaves, the feces left behind in the tunnels is. (Hope you weren’t eating as you read this.)
Controlling leaf miners in vegetables should start with cultural control methods including monitoring for the adults using yellow sticky traps, monitoring the leaves for larva and then removing the leaves if you can. Other cultural controls include using floating row covers over the plants as soon as you plant them to exclude the flies from laying eggs on the leaves, mixing your leafy vegetables with other crops as monocultures are prone to worse infestations, removing plants immediately after harvesting to prevent the pupa from entering the soil and working the soil in that area to kill any pupa in the ground. You should also avoid using excess nitrogen on leafy plants as this can cause leaf miner infestations to be worse. There are several natural predators that can help keep the leaf miners in check if you can encourage them to live in your garden.
If the infestation warrants it you can use chemical control. The tricky part about treating for leaf mining insects is that they are protected by the leaf itself so spraying the surface of the leaf is not sufficient to achieve control. With ornamental plants you could use a systemic insecticide to control the miners if the damage is severe but that is not an option for controlling these insects in vegetable crops. To treat for leaf miners, use products with the following active ingredients: Spinosad, permethrin, neem oil or horticultural oils. Only use chemicals to treat when necessary as resistance to several insecticides has been found in areas with intensive vegetable gardening and over use of chemicals has also been found to make infestations worse by killing beneficial insects.
