To Cope With The Spinach Leaf Miner

Many of you have expressed concern over your spinach plants that appear to be drying out. The farmer from Gateway Garden have done a little research and it looks like what we have here is aSpinach leaf miner. Removing infected leaves prevents the larvae from pupating, burrowing into the soil and returning later as egg-laying adults, which start the cycle of damage over again. This will be especially important for long-standing plants like Swiss Chard. In short, the eggs (white fleck on the underside of leaves) are the eggs of the Spinach Leaf Miner Fly, and once hatched feed on the tissue within the leaf. Hence, the name ‘leaf miner’. “ The maggots feed between the upper and lower leaf surfaces of the host plants mining out the tissue in between. As the maggot grows, the mines coalesce with others and blotches are seen on the affected leaves. It is not unusual for several larvae to be in the same leaf.” If you have the time an inclination, crushing those eggs on the undersides of leaves will limit hatching.

Prepare your site

​Since this insect overwinters as a puparium in the soil near where the crop was infested the previous year, crop rotation should be practiced especially if one tries to mechanically protect plants from this insect. Cover plants with fine netting or cheesecloth or floating row covers to protect them from adult egg-laying flies. Netting will not keep out insects that are already in the soil. Be sure that the edges of the row cover are well anchored so insects cannot get under them. The protective covering should be placed over the crop at planting time and, with spinach, might be left on until ready to harvest. Hand pick and destroy infested mined leaves when first seen before the larvae drop to the soil will help control the leaf miners. If leaves are just placed on a compost pile, fly larvae might continue to develop and emerge as adults to reinfest crops."

Double your harvest

Destroying the insects' wild food plants should also be  helpful in reducing  the numbers of leaf miners. This includes lamb's-quarters, chickweed and  nightshade in and around the garden.

 Control in beets

 Beets are typically not sprayed for leaf miners except if leaves intended for  consumption are infested. Use horticultural oil, or neem oil. Some products  require a longer number of days between application and harvest; check  labels. 

 Control in spinach

 If needed when mines appear and, if necessary, at seven-day intervals  thereafter (check label directions), apply neem oil, or spinosad.

Prevent problems

Most plants require about 1" of water per week. With little rain, be sure to water plants thoroughly. If using a sprinkler or hose, water plants early in the day to avoid evaporation during midday heat. Soaker or drip irrigation systems are more effective than sprinklers in that they provide consistent moisture to roots and conserve water. Adding organic compost and mulch can also help soil retain moisture. To prevent the buildup of pests and diseases, it is important to rotate crops. Plant crops (and members of the same crop family) in different locations each year. For additional tips on managing weeds and pests, see Common Concerns. 

Information provided by the farmer and mentor of The Gateway Garden