The battle with insect pets seems as old as time. Modern research has provided a new strategy for the fight, however, and understanding the enemy will help protect your garden.
Integrated pest management:
Today, integrated pest management (IPM) is the buzzword for gardeners seeking healthy trees and shrubs, with an economy of labor and a concern for the environment. IPM calls for planting resistant species, using natural controls, supplying fertilizer and water for maximum plant strength, and using pesticides only where necessary and always according to label directions.
Beneficial insects such as ladybugs, lace wings, syrphids (also called flowerflies or hover flies), mantises, and parasitic wasps are part of an IPM program. Encourage their presence by providing thick shrubs. These provide not only shade, but protection from predators such as birds. If you have several large shrubs on your property and want to nurture beneficial bugs, leave the bases of the shrubs untrimmed. That slightly untidy area is a favorite trysting spot for helpful insects, and under its protection they climb up the shrub or tree, often to deposit eggs. Leafy branches then cover both eggs and larvae and keep them high enough off the ground to avoid many predators. (Be aware, however, that this also provides cover for unwanted pests such as rodents. If you are having problems with mice or rats, you may be forced to rim shrubs further.)
Many garden centers offer a variety of beneficial insects for you to release in your garden. Once released, they are free to go where they please, but if you have provided appropriate living conditions, it is likely that they will remain to feed on pests.
Hopping insects:
Trees are afflicted with their share of these common pests. Some, such as leafhoppers, are extremely small. Others are weirdly shaped, such as treehoppers. And some are large and noisy, such as cicadas.
Cicadas infest both shade and fruit trees. Most of the damage they do results from egg-laying, which damages twigs. The twigs then turn brown and drop. Nymphs chew tree roots, and their feeding may eliminate both flowers and fruit. Adults suck sap from limbs and twigs. Broods of the periodical cicada may be large and destructive or small and merely an annoyance. Cicadas usually appear where they have appeared before, because trees harbor eggs from previous generations. As many as 40,000 cicadas have been known to infest a single tree.
Each brood may spend 13 or 17 years underground, feeding on tree roots, before appearing in masses above ground. The species with the 13-year life cycle is found primarily in eastern states; the 17-year species is found primarily in southeastern states. Cicadas are wedge-shaped and black-bodied. They have red-orange eyes and red wing edges. An adult’s full size is about 1˝ inches long. Males make the annoying high-pitched droning that seems to go on forever. The females puncture twigs with knifelike egg-laying organs. Each female deposits up to 600 eggs within the twig.
Cicada young, or nymphs, resemble brown ants when young. They drop to the ground and enter soil. For the 13 or 17 years they take to complete development, nymphs feed on tree roots. In May or June of a breeding year, they crawl up from the ground on tree trunks or almost any other available object. They change to adults and begin breeding.
Cicada control consists of monitoring cicada outbreaks. Where heavy populations are known to occur, avoid planting new trees while cicadas are visibly present. Prune damaged twigs where the female has laid eggs. To protect small trees, cover them with netting or cheesecloth during cicada outbreaks. Carbaryl sprays are effective against cicadas. Spray when the males first begin to drone, and respray after one week.
Plant bugs:
Small shield-shaped insects, plant bugs often live with leafhoppers. These insects are extremely mobile—they both run and fly when disturbed. They feed by sucking sap, and several species inject toxins as they feed. The tree parts attacked wither and die.
The plant-bug category includes many species. The four-lined plant bug is greenish yellow with black stripes and 1/16 inch long. It infests many ornamental trees and shrubs as well as cropplants. Leaves develop tan to reddish brown spots. The spots may join together to totally discolor the leaf. The sycamore plant bug, 1/8 inch long, is common on sycamore as well as ash, mulberry, and hickory trees. Feeding on leaves causes yellowish or reddish spots. Sometimes holes appear where dead leaf tissue has dropped out. The yucca-plant bug appears only on yucca, causing stippled leaves covered with black waste matter. The adult of the species is blue-black with reddish head and throat. Its nymphs are bright scarlet and may be plentiful on leaves.
Control plant bugs with a malathion or carbaryl spray when you first notice damage in spring. Make certain to cover both the top and undersides of leaves. Repeat as necessary.
Leaf-destroying insects:
Leaves plagued by insects may seem as if they are punctured with shotgun pellets, cut with scissors, the victims of a hole punch, or suddenly transformed into fine lace. Sometimes leaves disappear almost overnight. Leaf-destroying insects include leafcutter bees, rose slugs, cankerworms, Japanese beetles, alder flea beetles, leaf beetles, two-banded taxus weevils, bagworms, snails, slugs, mimosa webworm, holly leafminer, tent caterpillars, stain moth caterpillars, woolly-bear caterpillars, and gypsy moth caterpillars.
Insect pests of pines:
The increasing use of pines for reforestation, conservation, city areas, yard ornamentation, and holiday trees has caused an increase in pine-infesting insects. Many times the problem is a direct result of planting pines in clusters rather than mixing species in a natural way. Pine moths, pine sawflies, and other pests move quickly from one pine to another. Insect populations quickly build up to numbers natural predators cannot control. In general, avoid planting new pines near areas that contain pest-infested trees. Do not use bluegrass in pine-planted areas. Bluegrass encourages field mice, which may girdle pine trees.
Regular inspection of pines is crucial. Trouble signs include off-color foliage, unusual leaf drop, distorted growth, and insect presence. If caught in time, problems can be eased or eliminated. If you remove damaged pine wood, destroy it—prunings are an invitation to bark beetle invasions.
Information accredited to Ortho’s Home Gardener’s Problem Solver. page 130-131.
