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Archive for Wednesday, May 15, 1996

COMPANION PLANTS CAN WARD OFF PESTS

May 15, 1996

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Every year that I've put eggplant out in my garden I've done little more than make a sacrificial offering to the flea beetle gods. This year, I've sworn, will be different.

As the weather allows me to plant more vegetables in the garden, I'm also setting aside room for flowers and herbs. The idea is not only to add variety to my garden landscape but also to make use of the plants' ability to either repel or attract various insects.

With a little thought, it's fairly easy to create an environment that is uninviting to destructive insects but accommodating to their predators.

For instance, I've proven to my satisfaction that interplanting basil with tomatoes discourages the onslaught of tomato hornworms. The same aroma that I find seductive is repulsive to that particular nemesis.

I am applying the same strategy this year with my eggplant in hopes of short-circuiting its special magnetism for flea beetles. In this case the repellent is mint, which will be set in closed-bottom pots around the eggplants.

To appreciate my smugness about this, it's helpful to have experienced the profound dismay of discovering that flea beetles have ravaged your eggplant. They cause their destruction by biting small holes in the leaves, which eventually look like they've been used for shotgun target practice.

Because mint is invasive, it's wise not to plant it directly in the garden. Catnip, a member of the mint family, also is reputed to be inhospitable to flea beetles but it, of course, has the distinction of being particularly attractive to cats. Fear of luring every feline within miles to roll in my garden keeps me from trying this alternative.

In past years I've tried in vain to battle flea beetles with pyrethrum and rotenone, two naturally occurring insecticides. Any results have been short-lived, and continuous treatment is required. This can become expensive.

I've also used rotenone and pyrethrum on Mexican bean beetles, which chew larger holes in the leaves of bean plants. Although I've enjoyed more success using natural poisons to battle this pest, I always prefer a nontoxic alternative if there is one.

Even if you don't mind using pesticides, avoiding them means you won't inadvertently kill beneficial insects and upset the balance in your garden.

In the case of my beans, I'll be planting summer savory among the rows to make them less inviting to the yellow and green spotted beetles that have arrived every year.

In addition to using herbs here and there, I established three small flower beds in my garden last year and have seeded sunflowers around the perimeter. My objective is to attract an army of bees to speed pollination, as well as lady bugs to eat aphids and parasitic wasps to zap caterpillars and other destructive insects.

In filling these beds, I choose plants with shallow flowers such as zinnias and yarrow, which are accessible to insects with small mouth parts, a description that fits many predators, but not to those that chew leaves.

Companion planting isn't fool-proof and it may be only a partial solution. However, there's good reason to incorporate this strategy into garden planning, particularly if you might be growing a beneficial herb somewhere else.

Here's a list of herbs and the insects they're known to repel:

  • Artemesia: flea beetles, cabbage worms
  • Scented marigold: asparagus beetles. The roots of French marigolds (Tagetes patula) also emit a scent that repels nematodes, which makes them a good companion plant for carrots and root crops.
  • Coriander: aphids
  • Mint: aphids, cabbage pests, flea beetles
  • Catnip: ants, flea beetles
  • Basils: flies, some worms and caterpillars
  • Anise: aphids
  • Tansy: Japanese beetles, ants, flies
  • Rue: Japanese beetles

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