Garden Help Desk: How can I protect my beets?

March 25, 2019
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Beets with leafminer damage

Question: I think I can plant my beets in a few weeks, but I don’t want to have the same problem I had last year. I don’t know what you call the disease, but the leaves got large brown patches on them and dried out. I still got lots of nice beets, but I want to avoid that problem this year. Should I plant a special variety, or spray a fungicide or something like that?

Answer: Your description sounds more like an insect problem than a disease. There are small gray flies called leafminers that like to lay their eggs on spinach and beet leaves. Take a look at today’s photos and see if the plant damage looks like what you saw last year.

When leafminer eggs hatch on beet greens, the larvae enter the leaf and feed on the tissues between the upper and lower surfaces of the leaf. Their feeding leaves trails and patches of tissue that turn brown and die. At first glance, the leaves often look diseased. Once the larvae are ready to pupate, they drop out of the leaves and into the soil. Adult flies will emerge from the soil after pupation and lay eggs for a new generation of leaf miners.

Leafminer damage doesn’t affect the quality of the beets, but if you want to eat the beet greens, their damage is a problem. There are a few things you can do to reduce leafminer damage in your garden.

The most important thing you can do is give your beets good care. Water deeply during the summer, between once and twice a week, depending on your soil and the weather. Keep your garden weeded and watch for other insect pests.

Get in the habit of inspecting your beets frequently. Look for eggs and leaf mines. Eggs can be crushed by rubbing them between your thumb and finger. Leaves with leaf mines should be removed and disposed of; don’t just drop them in the garden.

You can also shallowly and carefully cultivate the soil around your beets during the growing season to find and destroy any pupae. In the fall after you’ve cleaned out your garden, cultivate the soil again to expose any pupae to predators and winter weather.

You can also use insecticides to target the egg-laying adults and the hatching larva. Larvae that are already feeding inside the leaves will be protected from the sprays. Choose a “soft” insecticide, like the active ingredient Spinosad, to reduce harm to beneficial insects.

Each year when you plant your beets, if you choose a different part of the garden for them and also cover your planting area with lightweight floating row cover. You might be able to protect your beets from leafminers for the first part of the season.

Q: I want to get a dormant oil spray on my fruit trees. The bud stage is about right, but there is rain in the forecast. I’m worried it will be too late to spray after this storm. What should I do?

A: A dormant oil spray will be useful even with a brief dry time, so go ahead and get the spray done when you can. Don’t spray while there are open flower buds, and you shouldn’t have any blossom damage problems.

Q: When can I spray my fruit trees? I want to spray some copper to control disease problems.

A: Spray copper just before bud break; copper sprays should have several hours of dry time, but 24 hours of dry time is ideal.

Note: Don’t spray for codling moths or cherry fruit flies yet.

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