What's eating your plants?

  • Article by: DEB BROWN , Contributing Writer
  • Updated: May 29, 2012 - 2:35 PM

Here are strategies for dealing with what's bugging your plants.

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Four-lined plant bugs

Our unseasonably warm spring has given many pests a head start in our gardens. Four-lined plant bugs and aphids are already feeding, and according to Jeff Hahn, extension entomologist at the University of Minnesota, Japanese beetles and earwigs should appear the third or fourth week of June in the Twin Cities. It's too early to know whether we'll have a bumper crop of bugs, but here are some strategies for dealing with them:

The bug: Four-lined plant bugs already are feeding on perennials, herbs and some shrubs. Nymphs can be found now -- they're small yellow insects with black blotches on their abdomens and a yellow strip on each wing -- but soon you may see the adults: greenish-yellow beetle-like bugs with four black stripes down their wings.

The bite: Their damage is so distinctive it's easy to recognize: They leave small, dark, circular depressions on the foliage, where they suck out the chlorophyll. Eventually these depressions drop out, leaving small round holes in foliage. This feeding can be both disfiguring and destructive, especially if there are lots of four-lined plant bugs in your garden.

The solution: There's just one generation of these insects a year. And because the adults are active for only about a month, they're not a problem all summer long. Although they rarely kill plants, some gardeners prefer to cut back or remove infested plants because they are unsightly.

If the damage isn't severe, learn to tolerate them. If they've damaged or killed some of your plants in the past, you might consider spraying them with an insecticide labeled for use against four-lined bugs. However, it's important to treat four-lined plant bugs as soon as you see evidence of their feeding.

The bug: Aphids -- tiny, pear-shaped insects that can be green, black, brown, pink or almost colorless -- are found on many plants throughout the growing season. They tend to cluster on stems, often just below flower buds, as well as on the undersides of leaves.

The bite: Aphids are sap suckers. While they're not likely to kill a healthy plant, large numbers can cause wilting and noticeable damage.

The solution: Aphids often can be removed with a blast from the hose. If that doesn't work, you can spray them with insecticidal soap or horticultural oil. Be sure to try a little of the soap or oil in an inconspicuous location first, however, to make sure it won't harm the plant.

The bug: Japanese beetles spend much of their life cycle as grubs in the soil. When they emerge, these oval-shaped beetles are easy to spot: they're about 3/8th of an inch long with green heads and bronze wing covers.

The bite: When they emerge sometime in June, they'll attack rosebushes, raspberries, grapevines and many other plants. They chew holes in the foliage until only the veins remain and they also devour flower buds. While flower buds can be destroyed, most survive a Japanese beetle infestation, but they look terrible. Successive years of attacks can weaken plants.

The solution: We usually don't see a lot of lawn damage from Japanese beetle grubs, but if heavy grub feeding damaged your lawn last summer, you could water insecticide into the soil this year. There are a couple of caveats: You have to treat when you first see the beetles feeding on your plants. Treating too early or too late is ineffective. And while soil treatment might slightly reduce the number of Japanese beetles next summer, it will have no effect this year. Even if you reduce the number of beetles that emerge from the soil in your yard, there's no guarantee you won't have them feeding on your plants because they can fly in from surrounding areas.

Pheromone traps, which lure the beetles to their death, don't work particularly well, either. Research has shown that the traps attract more beetles than they capture, including some that might not have come to your yard otherwise.

So what can you do? Knock the Japanese beetles off your plants into a jar of soapy water, where they'll drown. You may have to do this several times a day. If there are too many beetles to pick by hand, spray the plants with carbaryl (Sevin) or another insecticide labeled for Japanese beetles.

The bug: Earwigs are little (5/8th of an inch) brownish bugs with narrow bodies, short wings and antennae. They look menacing because they sport of pair of pincers at the tip of their abdomens, but their pincers aren't strong enough to bite people. Nor do they burrow into people's ears, as was once thought.

The bite: Instead, they feed on decaying plant tissue or insects. They also chew holes in healthy leaves, flowers and seedlings, leaving damage similar to that of slugs. And, like slugs, they hide during the day, coming out at night to feed.

The solution: Earwigs are attracted to dark, moist environments. They burrow in mulch, folded leaves and under debris. To create a less favorable environment for earwigs, try to keep the mulch relatively dry by watering heavily but less frequently.

An easy, chemical-free way to trap them is by setting out rolled-up newspapers in the garden at night. In the morning, shake the paper -- and the bugs -- into a bucket of soapy water.

If earwigs were a serious problem in your garden last year, you can spray or dust affected plants with a labeled insecticide when you first notice damage.

Deb Brown is a garden writer and former extension horticulturist with the University of Minnesota.

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