From time to time, most gardeners are faced with an invasion of unwanted creatures of the creepy, crawly, six-legged variety. Although it’s sometimes tempting to pull out the heavy artillery, this is usually not necessary, and it can even be counterproductive. Spraying with powerful insecticides often backfires by killing off natural predators while the pests develop resistance. So what can a person do to ensure that the garden is not overtaken by pesky critters? Many problems can be prevented or at least lessened with proper plant selection, siting and maintenance.
Choose disease resistant varieties, as healthy plants are less likely to be attacked by insects, and more likely to survive any invasions that do occur. When planning the garden, consider sun, soil type, drainage and exposure to wind. For example, do not try to grow German Iris in a heavy, wet soil, as the plants are likely to languish and rot, and weak plants are far more vulnerable to both insects and diseases. Likewise, trying to grow Delphiniums in a windy location is a battle the gardener is sure to lose. Planting in such a location would require serious staking effort. Even so, breakage would be extremely likely, leaving the plants subject to insect attack at the site of the damage.
Know the cultural requirements of the plants in question. Proper care can also go a long way towards preventing pest problems. Many perennials do not require a great deal of supplemental fertilizer, and too much fertilizer can result in overly lush, insect-attracting growth at the expense
of flowers. Take care not to over or under-water, and, if possible, avoid overhead watering late in the day. Foliage that stays wet into the evening encourages diseases and can lead to subsequent insect invasion.
Plant a diverse mix of plants. This helps to limit the spread of both insects and diseases, preventing them from running rampant through the garden. Crop rotation works in a similar way, preventing the build-up of pest populations from year to year.
Reduce weeds and clean up and dispose of dead or dying foliage. Weeds often act as co-hosts to both insects and diseases. Weed the garden thoroughly in the spring, and then use mulch between plants to discourage any re-growth. Clean plants of damaged foliage and remove any infected leaves that may fall to the ground. If not cleaned up, infected foliage perpetuates disease and harbors damaging insects over winter.
Encourage natural predators. Keep in mind that birds, bats, toads, frogs, snakes and predator insects are all the gardener’s friends. Encourage them to stay nearby by providing them with water and shelter. Consider having two birdbaths—one out in the open for the birds, and one in the flower garden for beneficial insects. Add some stones for the insects so that they may drink without drowning. A variety of shrubs and other plantings will provide habitats for many natural predators. Many beneficial insects also need pollen and/or nectar to survive. Most herbs are heavy pollen producers, along with carrots and the many members of the daisy family (Asters, Chrysanthemums, Black-eyed Susans, etc.). Try to include some of these plants in the garden mix.
While proper plant siting and care will reduce many pest problems, they won’t eliminate all unwelcome visitors. Keep in mind that some insects are innocuous. Sow bugs, for example, feed on organic matter in the soil and will not harm healthy plants. Remember, also that the predators need prey in order to survive, so it is often in the gardener’s best interest to accept low populations of pest insects. A hole or two eaten in a leaf is rarely a concern. A garden is never a
sterile environment.
If it is determined that control is necessary, start with the least toxic method. A strong blast of water from the garden hose can knock down populations of mites or aphids. Spittlebugs or caterpillars can be hand-picked and crushed. Knock Japanese beetles into a bucket filled with soapy water or a 10% bleach solution. Try paper collars to prevent cutworms from damaging vegetable transplants, and sprinkle diatomaceous earth or crushed eggshells around Hostas to prevent slug or earwig damage.
Insecticidal soaps and horticultural oils fall into the next level of control. They are effective controls for a number of pests, and safer than insecticides, but keep in mind that they can kill insect predators as well as pests. Timing of application is important with these products, and the product must contact the targeted insect. Be sure to follow instructions carefully.
Biological controls--Bt (Bacillus thuringiensis) for caterpillars and Milky Spore Disease (Bacilus popilliae) for grubs—are environmentally safer than insecticides because they are specific to those organisms. Be aware that Bt kills all caterpillars, though, so if butterflies are desired, try hand-picking first. Timing is critical with Bt. It must be applied when the caterpillars are feeding.
Botanical products such as Pyrethrum or Neem fall into the next level of control. While less toxic to the environment than traditional insecticides, they can be harmful to some beneficial insects. Again, follow directions carefully.
Traditional insecticides should be used with great care, and only as a last resort. Many are very broad spectrum, killing all insects, including honeybees, and many are toxic to fish. When properly sited and cared for, most plants are surprisingly resilient and will never need to be treated with an insecticide.
Date: April 11, 2000
Author: Maureen Safarik
Maureen Safarik is a Horticulturist at The Planter's Palette