CORVALLIS, Ore. – "Beetle banks" might not sound like something you especially want in your garden. On the other hand, like many gardeners these days, you may be looking for ways to cut back on the use of chemical insecticides, so incorporating habitat for beneficial insects is a sustainable practice that can help.
Rather than spraying wholesale to rid your garden of pests such as aphids, caterpillars, spider mites, mealy bugs, larvae and thrips, try letting their natural enemies do the work for you.
Mike Russell, a graduate student in the Department of Horticulture at Oregon State University, is researching the use of beetle banks – an agricultural practice begun in England and designed to encourage populations of beneficial insects. Beetle banks are mounds, or "banks" of soil planted with grasses and other non-crop plants where beetles, other beneficial insects, and spiders can establish healthy populations in agricultural fields.
Traditionally, before large tractors became common, European and British farm fields were plowed by a horse and farmer and were consequently small by today's standards. They were usually bordered by hedgerows, dense rows of trees, shrubs, perennials and annuals that provided habitat for small animals and insects.
As tractors displaced horses after World War II, many of the old hedgerows were removed and fields were enlarged. Habitat for beneficial beetles, other insects and spiders was lost, and what was left was farther from crops.
By the1980s, British farmers realized that by leaving banks of soil at intervals between the rows in their fields, perennial grasses could establish and provide habitat where beneficial insects and spiders could find shelter and survive the winter.
Ground beetles and rove beetles are two important beneficial beetle families that mostly walk rather than fly. During the growing season, having beetle banks close by makes it easier for these small slow-moving beetles to reach all areas of a large field.
With recent interest in sustainable farming, the use of beetle banks has spread beyond Great Britain. Russell says a few farmers in the Willamette Valley have begun incorporating the technique.
For agricultural use, beetle banks are typically four to six feet wide and the length of the field. For home gardens, something smaller, like "beetle bumps," might be more appropriate, said Russell.
Russell suggests leaving some perennial grasses, preferably bunch grass, to overwinter here and there. He's experimenting with various kinds of native perennial grasses that aren't invasive, monitoring temperatures and counting insects to see which plants are the most effective. While his research is still in its early stages, he says there is reason to believe that bunch grasses provide better habitat than sod.
Leaving some areas uncultivated also provides shelter for beneficial insects that fly, like wasps and hornets.
Adult insects need a supply of nectar for food every day, says Russell. Without a food supply, the flying insects will quickly find their way to more welcoming gardens. So it's necessary to have something blooming throughout the growing season.
Summer-long bloom isn't difficult to manage in flower beds, but in a vegetable garden it's not the usual practice. Consider leaving a few things to bolt and bloom, Russell suggests, like lettuce, spinach, arugula, or broccoli.
There are dozens of beneficial insects that you can encourage in your home garden. OSU's Integrated Plant Protection Center (IPPC) has produced a "Pocket Guide to the Common Natural Enemies of Crop and Garden Pests of the Pacific Northwest." This handy photo-illustrated guide will help you identify the good bugs in your garden. Download it at: Pocket Guide to Common Natural Enemies of Crop and Garden Pests of the Pacific Northwest.
Vist IPPC's "Banking on Beetles in Oregon" website to learn more about what OSU is doing to encourage growers to harness beneficial insects for pest control.