In this article we will discuss about the economic importance of pests in gardens.
The gardener is not alone in this battle for his plants’ health. Hordes of Nature’s creatures cooperate with him unwittingly in improving soil conditions and destroying harmful organisms. It is equally important, in the struggle to overcome the enemies of plants, to recognize, protect, and encourage these cooperators.
Earthworms and How they Help:
Well-nourished earthworms are one of the best indications of a soil good for plant growth. When given a well-drained, moist soil from moderately acid to slightly alkaline in reaction and ample organic material in the form of manure or dead vegetation, earthworms will mix and enrich many tons of soil annually.
Earthworms feed on plant remains in the soil, in the process of which they make burrows which help aerate the soil, and excrete casts of finely divided soil and plant material which is an important step toward making the nutrients therein available to plants. The numerous worm casts found on the soil surface in the morning or after rains help in the mixing of soil layers and make for a more uniform soil composition.
Unseen Hordes that Cooperate:
Not all bacteria are bad; many are definitely beneficial to plant life and should be encouraged. Experiments have shown that without these good soil bacteria, soil becomes barren and unfit for plant growth. One of the most important types of these soil microorganisms which produce great changes in the composition of the soil are the bacteria of decay. They break down the bodies of animal and plant material (organic matter) to such simple substances as carbon dioxide, water, and ammonia.
They thus release enormous quantities of nutrient material which growing plants utilize and which otherwise would be unavailable to the plants. They also take over where the earthworms left off and reduce the colloidal organic matter in their casts into plant nutrients. Nearly everyone is familiar with odor of ammonia issuing from damp manure or vegetable matter in the process of decay. That signifies that the bacteria are at work breaking down the material into water-soluble substances and making them available to plants.
Ammonia, one of the end products of bacterial decomposition, cannot be utilized by all plants, so here is where the nitrifying bacteria take over. They change the ammonia into nitrate salts, which is one of the chief nutrients essential to the growth of plants.
Yet another small group of bacteria, the nitrogen-fixing bacteria, have the remarkable ability to take nitrogen out of the air and make it into compounds which later become available to the plants associated with them. Some of these bacteria live freely in the soil; others are associated with the roots of peas, beans, clover, and other legumes, and produce small nodules on these roots. These fortunate plants can in this way obtain an abundant supply of nitrogen without drawing it from the soil. It has been estimated that the bacteria can fix yearly on the average of 80 pounds of nitrogen per acre.
These bacteria are present in most soils, but they may be purchased in the form of legume inoculants and mixed with the seeds of legumes at planting time to make certain that they do their good work.
Beneficial bacteria may be encouraged to work by plowing under green manure; keeping the soil from becoming too acid by liming; and providing ample moisture for the soil along with good drainage. Valuable ammonia may be prevented from escaping from decaying piles of organic matter by placing a thin layer of soil over the heap.
Recently still another bacterial organism has been harnessed and made to work against the enemies of plants. That bacterial organism is reared in the bodies of Japanese-beetle grubs. Many other bacteria and other micro-organisms too numerous to mention produce fatal diseases in animal and insect pests under natural conditions and help keep their numbers down.
Cannibals of the Insect World:
Nature has not provided its organisms with scruples, and, as a result, many insects prey on their close relations as a source of food. This is just what the gardener wants, and the more of these unscrupulous insects he can have about his garden, the safer the plants are from destructive insects. To learn to differentiate between beneficial and harmful insects is one of the important functions of the gardener, who, not infrequently, slays friend and foe alike.
The most common of these insect friends are the lady beetles, who, together with their larvae, consume countless numbers of aphids, scale insects, and insect eggs. When given time, these insects have been observed to clean up severe aphid infestations on fruit and vegetable crops. There are many different types of lady beetles, but the majority of them can be easily recognized by their brightly colored, spotted and rounded backs. Their larvae are also typically shaped and are usually black with some orange markings.
The lady beetles are not alone in their battle of extermination against the prolific aphids and other soft-bodied pests. Teaming up with them are voracious aphid lions, which are the larvae of delicate green lacewing flies; and the maggots of bee flies.
The gardener, in preparing or cultivating the soil, frequently turns up and unjustly kills many large flat black or metallic blue-bodied beetles. These are members of a large and varied group of night-hunting insects commonly known as ground beetles, which destroy many caterpillars and other insects in their nightly forays.
The gardener and his plants can also count on numerous other insects for help against pests. Among these may be mentioned the unjustly feared garden spiders and dragon flies; and the less frequently seen sharp-toothed and colorful tiger beetles and the robber flies, which capture insects in midair. The praying mantis is also a welcome visitor in spite of his ferocious appearance.
All types of pollinating insects such as bumblebees, honey bees, and bee flies, all of which are essential to the production of many fruits and vegetables, and the gardener finds that he is only one of many safeguarding the productivity of his garden.
Insects within Insects:
A most valuable group of large and tiny wasp like insects spend their immature stages as parasites feeding within the eggs or bodies of destructive insects which they eventually kill. In some fields hardly a tomato worm escapes a tiny wasp like insect. These parasites do not destroy the tomato worm until they emerge from the body and build tiny white cocoons all over its body—the caterpillar then sickens and dies. The green cabbage worm is similarly parasitized by maggots which build yellow cocoons on emerging.
Nearly every species of insect has one or more parasites that may attack it during some stage in its existence, and at times these are so helpful to the gardener that chemical control measures are unnecessary. Parasites are often reared under artificial conditions for release against certain insect pests. That is the only satisfactory means to date of controlling the Oriental fruit moth.
Mammals as Gardeners’ Assistants:
Many mammals who occasionally stray from the beaten path and acquire an appetite for domestic fowl have created such a bad reputation for their kin that they are killed on sight. This is a great injustice to them, as well as to the gardener, because ordinarily they are very effective consumers of rodents and insects. Numbered among these unjustly maligned animals are skunks, which consume great numbers of grubs and mice; red and gray foxes, whose main diet consists of rabbits, mice, and insects; and weasels, who can overcome rats and rabbits along with mice and insects.
Bats also, because of superstitious beliefs, are killed promiscuously; yet their main diet consists of insects. Shrews are tiny, shy, mouse like animals with short tails and pointed muzzles, which are deadly mouse and insect hunters, and are considered to be one of the chief causes of declines in mouse populations in fields and orchards.
Birds as Friends:
Some birds, too, are ruthlessly killed by those who do not know the full facts. Such destruction is unwarranted on the basis of the benefits generally derived from their presence and activities.
The chief sufferers of this misunderstanding are the hawks and owls, who do at times attack poultry, but who, at the same time, are excellent destroyers of rodents such as rats, mice, rabbits, and squirrels. Crows also have a bad reputation, yet their main diet is made up of insects.
Most of our common birds feed chiefly on insects and weed seeds, but occasionally become troublesome on fruits. Their damage to fruits, however, rarely warrants their destruction, and other means should be used to prevent damage. Flocks of birds have been known to save whole fields of crops by devouring heavy insect populations, and some nestling birds consume more than their own body weight of insects daily when fed by their parents. Birds may be attracted to gardens by planting various types of berried shrubs; by erecting proper types of bird houses; and by erecting bird-feeding stations in the wintertime.
Snakes and Toads are Friends, too:
Most people fear all reptiles instinctively and kill them on sight; yet most of our common snakes, such as milk snakes, green grass snakes, and striped garter snakes, feed mainly on small rodents and insects, and should be considered beneficial.
The rattlesnake and the copperhead are the only poisonous species in the northeastern United States that should be killed on identification. The copperhead is sometimes confused with the milk snake, because of some similarity of color and markings. The milk snake is also mistaken for a rattler because it vibrates its tail against the ground or foliage, producing a sound not unlike a rattle.
Its sharp hiss and inclination to strike also gives people the idea that it is poisonous. The copperhead may be distinguished by its coppery-red head and series of chestnut-brown hourglass-shaped markings running down its back when viewed from above. The timber rattlesnake found in the East is brownish or bluish, with fairly wide black or dark-brown V-shaped cross bands.
Both the copperhead and the rattler have a pit on each side of the head between the eyes and the nostrils. Toads feed mainly on insects. The common small garden toad usually comes out at dusk to get his fill of insects, and during the day remains hidden in the soil.