Archive for Wednesday, June 23, 1999


June 23, 1999


Insects are both a vital and unavoidable component of the garden environment. While some damage the vegetables we plant and may need to be controlled, others perform good works, as pollinators and destroyers of harmful insects, and should be spared. That's the tricky part of managing the bugs in your vegetable garden.

The list of good bugs includes the lady beetle, which eats aphids and looks pretty; bees, which help pollinate many of the vegetables that bloom to set fruit; the spined soldier bug, which eats caterpillars, grubs and the larvae of flies and destructive beetles; ground beetles, which prey on root maggots, cutworms and beetle larvae; and tachinid flies, which closely resemble house flies and eat caterpillars, many beetles and squash bugs.

You can encourage lady bugs and the bees that act as pollinators to come into your garden by planting small beds of perennial flowers inside the garden. This also gives beneficial insects a place to hide when you do use pesticide and a place to overwinter.

My list of unwelcome bugs is fairly short but my history with these insects is such that their appearance is usually enough to spur me to action.

  • Squash vine borers: This is Gardener's Enemy No. 1, given the swiftness and completeness of its destruction. Within hours, these insects can annihilate a squash, pumpkin or melon plant.
  • Squash bugs: The little gray bugs lay their eggs on the undersides of squash leaves and chew the leaves and suck juice from the stems.
  • Blister beetles: It took me awhile to figure out what these were, since there are so many variations of this bug featured in pest books. The ones I battle are dark gray and attack both the leaves and fruit of tomato plants. Even before you see them, you know they're there because they leave disgusting black droppings all over the plant. They are poisonous and will blister the skin if you squish them in your hand.
  • Flea beetles: These tiny black bugs love eggplant. The leaves of an infested plant will be riddled with pin-sized holes.
  • Mexican bean beetles: These are kin of lady bugs. They are spotted like the lady bug, but their dominant color is yellow, rather than red or orange. They chew through the leaves of bean plants and take bites out of the bean pods.

Left to their own devices, the insects that populate a vegetable garden will do battle and take and cede territory. The beneficial insects in the garden will do their part to control the bugs that destroy plants, just as the pests will target growing vegetables for food and habitat. When the balance they strike does not suit the gardener's standards and we start finding holes in leaves and damaged fruit on the vine, that's when we have to make a decision about using pesticides.

The problem with a broadly effective synthetic pesticide is that it not only clobbers our enemies but also the insects that assist with pollination and kill the larvae of emerging pests. It's like calling in a SWAT team when a fly swatter will do.

When I resort to pesticide, I first try rotenone powder, which is a plant derivative rather than a synthetic pesticide. Rotenone is supposed to be safe for most beneficials but it's highly effective for the targeted insects so I suspect it kills its share of good bugs, too. By dusting only the plants under attack, I can minimize the damage to the beneficial insect population.

A more potent plant-derived pesticide is pyrethrum, and I go for this one first when it comes to squash bugs and vine borers. Again, I treat only the affected plants and the area immediately around them, since the bugs do swarm on the ground near the vines.

Read the label precautions. As a general rule, however, these plant-derived insecticides can be used on vegetables up to the day before harvest. Be sure to wash your vegetables thoroughly. By comparison, waiting periods of 14 days are not unusual for vegetables treated with synthetic pesticides.

Worms are also a problem in the garden. Tomato and tobacco hornworms rarely arrive in large numbers and can be controlled by hand picking, however one worm can wreak havoc on a tomato plant.

Corn earworms can be controlled with pesticide but I generally leave them alone. They chew into the ends of corn ears but only rarely do they decimate an ear. I'm content to let them have the top inch, which I cut off during shucking.

If you decide you need to declare war on worms, BTK, a variation of bacililus thuringiensis, is a microbial control for caterpillars. The caterpillars die when they eat plants treated with it.

-- When she's not writing about foods and gardening, Gwyn Mellinger is teaching journalism at Baker University. You can send e-mail to her at Her phone number is (785) 594-4554.

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