Earwigs chomp on marigolds

My marigolds are all being eaten by something invisible. I thought nothing eats marigolds. What’s chewing on them?

— Betty

What you are seeing is feeding damage by earwigs. I’ve come to think that it is a myth that nothing eats marigolds.

Earwigs are dark brown beetles with pincers on their hind ends. We used to think they wouldn’t hurt plants because their mouth parts aren’t that strong, but in the past several years we’ve found that they can cause plant problems.

Earwigs mostly feed on soft, decaying organic matter and sometimes soft fruits such as strawberries. However, they also will feed on new succulent growth of plants. We see their feeding damage mostly on marigolds and butterfly bushes. They just eat the leaf tissue between the veins, leaving a lacy, skeletonized appearance.

You almost never see them feeding on a plant because they hide in moist, cool shady spots during the day and come out at night. It might surprise you how many are lurking around your flower bed and seemingly overnight, the leaves are gone.

The best way to get rid of these little devils is to spray with a synthetic pyrethroid insecticide such as permethrin or bifenthrin. This group of sprays is pretty safe for people, pets and birds but does a great job on insects.

Spray plants twice, about 10 days apart. Completely cover them and spray the ground several feet out from them.

My daughter has about eight aspen trees that border her patio. The other morning she woke up to find that aphids were on her trees, so she sprayed them with water. The next morning they were still there, so she sprayed them with a water-soap solution. Now the leaves are turning black and falling off. Do you have any idea what is causing this?

— Bob

The water-soap solution may have burned the tree. The soaps dissolve the waxy skin, called cutin, of the aphids so that they desiccate and die. It’s basically skinning them alive. Kind of gruesome, but heck, they’re aphids after all.

The problem is the leaves of plants have that same waxy cutin. If the soap solution is too strong, it kills the aphids, but it also strips off the waxy skin of the leaves, burning them.

The trick is to have the soap solution strong enough to kill the aphids but not so strong that it strips the wax off leaves. I don’t have a mixture to give you because it varies on what the weather is doing. When it’s cooler and more humid, the leaf can withstand a stronger spray, but now that it’s hot and dry, there’s no margin for error.

Next time, she should use a commercial insecticidal soap. They’re formulated to kill the insect but not harm the leaf. They can still burn foliage, but they’re a lot safer than mixing your own with dish soap.

Actually, if she just kept up spraying the tree with plain water every day or two, she’d see those aphids disappear in a couple of weeks. If she waited two or three weeks, the ladybugs, lacewings and other predatory insects would probably control them.

For now, she should just hang in there with the trees; there’s probably no real long-term damage.

Dennis Hill is the nursery manager at Bookcliff Gardens, bookcliffgardens.com. Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or email .(JavaScript must be enabled to view this email address).


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