Swiss Chard Leaf Miner

(Question)

Hi there,

After a bit of research, I’ve concluded my Swiss Chard definitely has leaf miner issues. Some of the leaves have white, wilty bits, and some leaves also have the small oval eggs on them.

I’ve been pulling all affected leaves, and throwing them in a garbage far away, but I basically don’t have many leaves on my chard left.

I planted the card a bit late in the season–put the seedlings in on the May long weekend.

I don’t know if the problem will get better if I just keep pulling the affected leaves, or if I should just dig up the chard and try something else? I don’t know if the yields will be very good in the summer anyway…

Any advice is appreciated.

Thanks!

 

(Answer)

Vegetable Leaf Miner, Liriomyza species (there are several types that eat vegetable crops) burrows through the leaves leaving wiggly white lines, which eventually cause dead patches on the leaf. In spring the Leaf Miner Fly lays eggs under the Chard leaves. Small white oblong eggs, up to 5 in a neat row. The eggs hatch and the caterpillars eat their way through the leaves for several weeks before falling to the ground where they pupate. The flies emerge after several more weeks and lay a second round of eggs. The second round pupate in the ground over winter and emerge as flies in the spring.

Removing the infected leaves, like you have been doing, reduces the population significantly. The Cornell University Horticulture Diagnostic Laboratory (HDL) give a detailed description of insect identification, life cycle and treatment (see link). For this season you can continue removing leaves, keeping the plants well watered, offering them an application of slow release vegetable fertilizer (14-14-14), some organic compost (if you haven’t already) and mulch to reduce evaporation, weeds and to make it difficult for the pupating grubs to burrow into the soil. This may give your plants a chance, if it was a small infestation. If all of your plants are stripped of most leaves, then removing the plants and disposing of them in the garbage would be easier and more cost effective.

You need to plant leaf miner resistant species if you use the same site. There is a lot of on going research into vegetable resistance, with new species being developed, so talk with your nursery to see if they carry more tolerant species.

For next spring, Cornell HDL recommend rotating your crop, so the emerging flies have no food source. This could work if you have a spot somewhere else in your garden to grow your chard. You could also plant an alternative resistant crop in the infected site. If you change sites next spring, you can protect your chard crop with a floating row cover or fine netting, secured at soil level after planting, to prevent the flies from laying their eggs.

Keeping the plants vigorous, with water, organic compost and mulch, can reduce the effects of any local infections. Your crop was quite young this year when the flies laid their eggs, so the Leaf Miner Fly had the upper hand. Next spring, try to get your plants in as soon as the snow melts and the ground can be worked. They are quite cold hardy.

https://ccesuffolk.org/assets/Horticulture-Leaflets/Spinach-Leafminer.pdf

 https://www.omafra.gov.on.ca/english/crops/facts/00-039.htm