Summer garden bug wars

  • Article by: JANE FRIEDMANN , Star Tribune
  • Updated: July 28, 2009 - 1:25 PM

Here are a few of the more common critters you may come across and some strategies you can use to combat the bugs on the wrong side of the battlefield, while encouraging those that are on your side.

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You may not see them, but the signs are there: damaged heads on your broccoli, wilted delphiniums, chomped tomatoes. You may not have them bad, but every garden has bad bugs. Knowing that beneficial bugs far outnumber bad ones is scant comfort when faced with a ravaged garden.

So here are a few of the more common critters you may come across and some strategies you can use to combat the bugs on the wrong side of the battlefield, while encouraging those that are on your side.

THE BAD BUGS

APHIDS

Size: About the size of a pinhead.

Threat: They suck plant sap, causing foliage to yellow, curl or wilt. Some aphids are winged and can transmit disease from plant to plant.

Host: Many, including kale-family vegetables, root vegetables, leafy greens and flowers including roses, mums, delphiniums and geraniums.

What you can do: Aphids generally don't significantly harm healthy plants and they attract beneficial bugs to your yard. Horticultural oil can be used in late winter to suffocate eggs or in spring and summer to kill nymphs and adults. Insecticidal soap, Neem or Naturalis-O also are effective and have little impact on beneficial bugs.

TOMATO HORNWORM

Size: Up to 4 inches

Threat: Young caterpillars feed on the upper leaves of plants, creating dark green or black droppings. Older ones increase defoliation and may eat the fruit of plants, as well.

Host: Tomatoes, sometimes potatoes, eggplants and peppers.

What you can do: Keep garden as weed-free as possible. Handpick hornworms and drown them in soapy water. Till soil after harvest to destroy burrowing caterpillars. Several insecticides are appropriate for use if handpicking is not practical, including insecticidal soap, bacillus thuringiensis and spinosad.

SQUASH VINE BORER

Size: About 1/2 inch

Threat: Adults lay eggs singly at the base of plants. In about a week, the eggs hatch and the larvae bore into stems to feed, blocking the flow of water to the plant. Plants wilt and eventually collapse and die.

Host: Summer squash, winter squash, pumpkins and sometimes cucumbers and melons.

What you can do: Watch for these buzzing insects starting in late June. At first sighting, spray or dust pesticide on the base of plant stems. Repeat every seven to 10 days until the end of July. For a chemical-free approach, cover the vines with securely anchored floating row covers as soon as you see any borers. Leave row covers on for about two weeks. If larvae tunnel into vines, the plant's prognosis is poor. As a last resort, try carefully slitting affected vines lengthwise until larvae are found. Stab the larvae to kill them, then bury the slit section of the vine and water well to encourage it to root.

SLUGS

Size: From 1/4 inch to 2 inches or longer

Threat: Slugs begin feeding as soon as they hatch and are partial to garden plants with large leaves or plants that grow close to the ground. They flourish in cold, wet weather and are more active at night.

Host: Many plants including delphiniums, geraniums, lettuces, pears, rose leaves, strawberries, hostas and tomatoes.

What you can do: Keep the surface of garden soil fairly dry by raking up debris, pruning lower leaves and watering in the morning rather than the evening. Trap slugs with damp newspapers laid out overnight. Check under paper in the morning and crush slugs or spray them with a diluted ammonia solution. Some insecticides are effective against slugs.

THE GOOD BUGS

LADY BEETLES (LADYBUGS AND LADYBIRD BEETLES)

Size: 1/4 inch or less

Benefit: Both adult and larval ladybugs actively consume pests such as aphids and scale insects.

How to attract: Buying ladybugs is not a good idea. If you don't have ladybugs already, the purchased ones probably won't stick around, either. Instead, plant a wide variety of flowering plants that bloom at different times and be careful about using pesticides in your garden.

ASSASSIN BUGS

Size: 1/2 to 3/4 inch

Benefit: Assassin bugs are real generalists. They eat many pesky insects by stabbing them with their proboscises and injecting a toxin that dissolves tissue. The bugs then suck out the tissue.

How to attract: They are partial to gardens well mulched with organic material. Plant a variety of small-flowered plants. Don't handle assassin bugs; they bite when they feel threatened.

HONEYBEES, BUMBLEBEES, SOLITARY BEES

Size: 1/2 to 1 inch

Benefit: Bees are the major pollinator of flowering food crops. Honeybees provide us with honey and wax. Since 2006, honeybee populations have been hard hit by colony collapse disorder, a mass disappearance of worker bees probably brought on by pesticide use, loss of habitat and parasitic mites.

How to attract: Avoid using pesticides on flowering plants. Plant a wide variety of flowering plants such

as bee balm, gaillardia and coreopsis.

DRAGONFLIES AND DAMSELFLIES

Size: 1 to 4 inches

Benefit: They eat many insects, particularly gnats and mosquitoes.

How to attract: Install a garden pond. (Find out how at www.nwf.org/gardenforwildlife/dragonflies.cfm.) Avoid using pesticides. Don't use a bug zapper for mosquitoes; they zap dragonflies, too. If you have outdoor cats, you may only be enticing dragonflies to their grisly deaths.

Sources: Jeff Hahn, entomologist with the University of Minnesota Extension Service; Nancy Rose, horticulturist with the Arnold Arboretum of Harvard University; Minnesota Landscape Arboretum; National Wildlife Federation.

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