Garden pests' natural foes

Insects: Bugs vs. bugs -- that's the theory behind biocontrol.

July 25, 1999|By Nancy Taylor Robson | Nancy Taylor Robson,Special to the Sun

It's a jungle out there, a pitched battle between gardener and voracious pest. Although I don't mind sharing a little, I resent the 50/50 split the marauding bugs often try to take. Yet, while I feel murderous toward greedy garden pests, I want to protect the birds, toads, and helpful insects. And by some estimates, 98 percent of insects are beneficial to the human enterprise. The trick is to thwart the others, the ones chowing down on your produce.

One solution: Enlist their natural enemies -- other insects.

These days, it's possible to order up a pint -- or a gallon even -- of a beneficial bug. Many garden catalogs sell everything from ladybugs to lacewings. Customers usually order by phone or online. Within a week or two, the bugs arrive in the mail.

"We try to tell our customers when they're coming so they don't sit for a day and a half in a black mailbox in the sun," says Craig Harmer, entomologist at Gardens Alive!, a catalog company that sells bugs and garden products.

There are benefits to biocontrol -- the practice of using an insect's natural enemies against itself.

Robert Shroder, a researcher at the Beltsville Agricultural Research Center, is exploring this option for the corn rootworm and the Colorado potato beetle, which ravages potatoes, eggplant and tomatoes.

"I am searching ... for beneficial organisms, including parasites, predators and pathogens, that can be ... used against these pests," he says.

One reason Shroder seeks biological controls is that in addition to the cost and the environmental concerns insecticides raise, pests are developing resistance to them.

The key to successful use of beneficial bugs is figuring out what's demolishing your plants.

"It's crucial to get the pest identified," says Harmer.

There are several ways to do this. You can go into the garden, insect guide in hand, and examine the plant damage and, probably, the culprit. Harmer uses "The Colored Handbook of Garden Insects" by Anne Carr (Rodale Press, $21.95).

"It has really nice pictures, and groups them so it's easy to understand," he says.

Or, you can call the county extension agent.

"Give a description of what the insect looks like, what plant it's on, and when it came," Harmer ad- vises. "They can probably tell you what it is over the phone. Or, you can bring it in and show them."

Prior to identification, be careful what you kill. Most people know what a ladybug looks like, but not the larvae, which is just as helpful.

"Immature beneficial insects often look a lot different from the adult," notes Harmer.

The saviors of the natural world, ladybugs each consume over 5,000 pests in a lifetime. Other less well-known bugs can also do yeoman service in the pest wars. Assassin bugs, for example, which look like black moon buggies with orange headlights, eat Mexican bean beetles. Praying mantis eat any insect they can catch. In late spring, their butterscotch-colored kumquat-sized cocoons disgorge swarms of little eating machines.

If you've got a heavy infestation, you may want to spray before ordering bugs. "For example, if you have aphids all over your roses, you're probably going to have to use something first to knock them down such as an oil or insecticidal soap," says Harmer. "Then you can bring in the beneficial insects to continue to take care of them. But, once you've released the beneficials, you shouldn't spray most products after that."

Release timing depends on what you're ordering -- for example, aphids start munching on roses at the end of May and continue into July, (so from May on, ladybugs will have prey), while beneficial nematodes can be put out as soon as the soil is above 55 degrees and can continue all summer.

On arrival, remember that these are living organisms. Although it's better to release them immediately after they are delivered, the cooler late afternoon is optimum. If necessary, you can put them in the refrigerator for a couple of hours to cool if they arrived in the middle of a scorching day. "And give them water," Harmer adds, "by misting rose petals or whatever vegetation you're working with."

Not all beneficial bugs arrive prepared to take wing. Lacewings (which attack aphids, mealybugs, immature scales and whiteflies, as well as the eggs of mites, thrips, spider mites and others), arrive in the larval stage, hungry and mobile, but not flight-ready. Ladybugs are shipped as adults, and the trichogramma wasps (which eats gypsy moths, Oriental fruit moths, asparagus fern caterpillar, cutworms, and fall webworms among others) arrive in pupal form to emerge as adults a short time later.

These buys can be an economical way to protect your garden. A package of 900 Sta-Home Lady Beetles costs $13.99 in the Gardens Alive! catalog. The Grub-Away Nematode is an even better deal: 5 million for $13.90.

But how to keep them in your yard? If you have an infestation of pests they like, the good bugs are likely to stay close to their food source. To help the beneficial population stay nearby and multiply, provide a floral smorgasbord.

"Fennel, dill and small flowers will give them a sugar source," Harmer says. As a rule of thumb, nectar-bearing flowers attract and sustain beneficials.

Results of beneficial bugs vary with soil condition, plant health, the extent of the infestation and weather conditions. Some people see a difference overnight; others wait days or weeks.

Sources:

* Gardens Alive!

5100 Schenley Place

Lawrenceburg, Ind. 47025

812-537-8650

* The Beneficial Insect Co.

137 Forrest St.

Fort Mill, S.C. 29715

803-547-2301

http://bugfarm.com/

* March Biological

26115 Chehalem Station Road

Sherwood, Ore. 97140

503-554-1077

800-328-9140

Fax 503-554-0182

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