Description
Leafminers belong to several different genera of insects such as beetles, flies and moths. It is simple to identify a leafminer as they 'mine' through the leaf and cause damage that is unmistakable. As larvae tunnel their way through the leaf layers eating chlorophyll and other plant juices, they leave a white winding trail behind. Scouting can be done during the day when there is light to see these symptoms. Although leafmineres rarely kill a host outright, they can ultimately weaken the plant's ability to photosynthesize, which can result in stunted growth, discoloration, or even open a wound for which disease can enter. Also, in the case of leafy greens such as lettuce and spinach, leafminer damage can cause the crop to become less profitable.
Target Crops
A variety of vegetable crops, but particularly leafy greens such as spinach, lettuce, swiss chard, etc. They also tend to enjoy Aquilegia, which can be used as a trap plant, as mentioned below.
Life Cycle
Females lay eggs underneath the plant's epidermal layer on the leaves. Larvae hatch and burrow through the leaf tissue feeding on chlorophyll. After 2-3 weeks they are ready to pupate and burrow into the soil where they will emerge roughly two weeks later as adults. Multiple generations can occur each year.
Beneficial Insect Control
Steinernema feltiae is a beneficial nematode species that can be an effective biocontrol. These parasites can be applied to the soil to infect and help control an array of soil-dwelling pests. Leafminers overwinter in the soil as pupae, giving nematodes the opportunity to pounce, while not harming other beneficial inhabitants in the soil. See our Beneficial Nematode Tech Sheet for application rates and best practices.
Diglyphus isaea is a parasitic wasp that stings and paralyses the leaf miner larva while it feeds in the leaf tissue. Diglyphus females lay their eggs alongside the host, and after the eggs hatch they feed off the fluids of the still alive, but paralyzed larva. Each female wasp can kill over 300 leafminer larvae!
Release 0.25-0.5 predators per 10 sq. ft. for effective coverage, with two back to back introductions over a 2 week period recommended. To release, hold the bottle horizontally and remove the lid. Release the parasites by gently tapping the opened bottle while walking through the crop. Leave the open bottle upright in the infested area for a few hours to allow any remaining parasites to escape. In hot sunny weather, release early or late in the day. Do not cold store adults for more than 18 hours, holding in darkness at 55-60°F.
Insecticide Options
Products where neem oil is listed as the main ingredient are great for spray applications. Other products with leafminer on the label are Grandevo, Azatin O, Pyganic, Molt-X, PFR-97, and Venerate XC.
Cultural Control Tips
- To encourage Diglyphus isaea in your system, plant flowers such as dill and yarrow, which are rich in pollen and nectar, giving the wasps an accessible food source.
- Leafminers tend to enjoy Aquilegia spp., so consider utilizing these 'trap' plants in adjacent areas to the field to draw leaf miners away from vegetable crops.
- Use yellow sticky cards in crops to trap adult flies
