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Battling a Swiss Chard Pest

Every year, the leaf miners ruin my Swiss chard all summer. Maggots in the leaves, with their accompanying frass (bug doo) render it rather unappetizing. In past years, I have sprayed with summer oil every week, or as often as I can remember to do it, but the improvement has been only slight.

I have been reading about a new product, called Spinosad, and have finally tried it on my Swiss chard. About a week and a half after the first spraying, there seem to be fewer new injuries. I also sprayed spinach that was being damaged, with similar results. Tomorrow, I will clean up the plants and spray it again.

Spinosad (also sold as Bulls-Eye), is made by fermenting the bacterium Saccharopolyspora spinosa. Two of the metabolites of this bacterium (that is, products of its metabolism) are highly toxic to a number of insects. It is said to stop susceptible insects from feeding in one hour, and remain toxic to newly arriving insects for the next week or two. It is also said to spare lady beetles, lacewings, and minute pirate bugs, all creatures that eat pest insects in our gardens. It breaks down in sunlight and does not persist in soil. The amount of time to wait after spraying before you harvest varies, but for Swiss chard and other leafy greens, it is one day. It is OMRI, meaining approved for use by organic farmers.

At this point, I don't know every detail about this material, but if the leafminers desist from mining in my Swiss chard leaves, I will find out the ones I don't know yet and report them. It is also said to kill thrips, caterpillars, sawflies, and a number of other pests. (A critter called a rose slug is a sawfly larva. I see it on San Francisco roses often. Summer oil is relatively effective against it, but for serious infestations, Spinosad may be just the ticket.)

By the way, the leafminer in the chard and spinach is the larva of a fly (therefore it's a maggot) that eats out the inside of leaves, causing ugly blotches.The fly lays eggs on the leaves of chard and spinach; the larvae hatch out and enter the leaves. When they have eaten their fill, they drop to the ground to pupate. When they emerge from the pupae, the flies breed and lay eggs again. This goes on in the warmer part of the year here in San Francisco, from late March until mid-October. (Chard and spinach growing October to March are safe, but you have to start them earlier than mid-October for good winter production.)

The fact that the pupae live in the soil means that beneficial nematodes watered into the soil might help as well. I am thinking of getting some this year. These microscopic creatures that you can purchase are only effective when the soil is warm, so I will wait a few more weeks before adding them.

Comments

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Larry

Is a sprinkling of Diatimatious Earth of any use? What about 2 cups water & 2 teaspoons of dishsoap (w/o Bleach), & maybe the addition of diced hot peppers (~1/2 cup) &/or garlic (~5 or so cloves crushed)? I believe you put the dishsoap in after you have let the other ingredients brew for 24 hours & strained the pulps out. It is supposed to work with spittlebug, & I heard similar remedies work against ants & aphids. I`ve also heard/read 10 parts water to 1 part vinegar works against aphids, I think. I am returning to gardening just recently, after not having done much of it, except weeding, since I was less than 10 years old. I am surprised at how few of the details I am now, or then was barely aware of, because my mother or grandmothers must have been attending to it back then. I know that we had pests, & I know they did things, many with simple household materials & a spray bottle, but I apparently wasn`t pay as close attention as my adult self wanted to believe a few months ago.

Larry McMahan


This is great news to me! My swiss chard has been ravaged by these pests this years. It just happens that I have been spraying my Cherry tree for Spotted Wing Dorsophila (Cherry Vinegar Fly) with Spinosad. I will just start spraying any chard which I plant also. I was wondering what I was going to do other than wait a year or two for the leafminers to leave. Great info!

Lynette

I too have had this problem with my beets and chard for about two years! I read an article in the Chronicle regarding this pest, and have been picking the leaves faithfully but nothing has made it stop and it's now almost December. I have even tryed food grade DE like I use on my brasicas! Next step will be the Bulls-Eye as we love our greens!

Pam Peirce

Hi Keith,

I am perplexed by your "unseen bugs." By skeletonized,do you mean they ate all the leaf except the midrib and large veins? Can I ask where you are gardening? Are you in the SF Bay Area? Have you looked at your chard at night, with a flashlight to check for nocturnal pests? I'd like to figure out what the pest is before you choose a pesticide.

Keith

I had unseen bugs that skeletonized the leaves of my Swiss Chard this year. The "frass" mentioned in the article was present at the end (before my plants died!) I think most of the larvae were gone by the time I tried harvesting, and even the stems seemed damaged. This was the first year I had this problem, as Swiss Chard is pretty reliable normally. Also, in answer to the previous post, none of my lettuce was affected - just the Swiss Chard. I may try some rotenone next season as it breaks down fairly quickly before harvesting.

Richard

This information has saved me a trip to the nursery and I thank you for that. I also have romaine and red leaf lettuce in the garden and currently haven't seen any problem yet. Do they eat lettuce too ? Thanks for any help.

Teri in Minneapolis

Sticky paper also helps by trapping the flies and interrupting the reproduction cycle. I remove the leaves that have been mined or just the affected parts on larger leaves. Early intervention is important--if you catch it early the odds of success are better. Bulls Eye sounds fishy to me! Neem is supposed to help but I had no luck with that.

chard man

Leaf miners are no problem. Wash the eggs of the leaves every few days. If you somehow miss one and they get into the leaf, cut the mined part right out of the leaf.

I have a 100 percent success rate this way.

pam

Charlene,

You can't get rid of leafminers by washing the leaves. The larvae live inside the leaf, between the top and bottome "skins" of the leaf. They lay eggs at first, on the outside of the leaf, and you can brush these off, but then the eggs hatch and enter the leaves.
The leafminer larvae wouldn't survive being eaten by you. They are totally incapable of surviving inside you and do not parasitize anything but spinach, beets, and Swiss chard. Most people wouldn't want to eat them due to the ugh factor, but they would just be, as they say, extra protein, nutritionally speaking.
In order to avoid eating them, most people would cut away the part of the spinach or chard leaves that had damage, problem being, of course, that if spinach leaves aren't very big, you might not have much left to eat.
There is more on this pest in later posts, including ideas for controlling it. Do a search for "chard" to find them. There are photographs.
Yes, gardeners often, within reason, wash off the pests and eat the rest, but this one is a hard one to deal with once it is in there.
If you don't mind, I would like to consider your question for a column that I write for the SF Chronicle (and sfgate.com).

charlene

I have a question, as I am a new gardener. Is it OK to eat spinach that has had the leafminer larvae on it? I have just painstakingly washed, leaf by leaf, a small harvest of spinach, brushing the larvae off each until I am sure they're gone. The last thing I want is to contract a parasite. I don't know what is safe or standard practice in terms of eating from an imperfect garden. Advice??

charlene oneil

where to buy bulls-eye in Bay area?

pam

I don't have any info about boric acid and leafminers. Boric acid is effective against ants. The link provided in the previous post is a link to a site dealing with indoor pests, not garden pests. I don't recommend use of boric acid for leafminers in the garden.

dee

Boric acid is very effective against these pests . From http://pests.in

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