Phyllosphere is a term used to refer to the environment in the areas
of the aboveground portions of a plant, especially the leaves. It
attracts many insects. The study of insects is called entomology
and a horticulturist must learn to recognize the beneficial and
harmful insects in a garden. Insect pollinators are beneficial.
Insects that eat plant parts are destructive. Common destructive
insects are mealy bugs, aphids, white flies, thrips, caterpillars, and
grasshoppers. Plant viruses are often spread from plant to plant
by aphids and thrips, as well as mealybugs and some leafhoppers,
so you need to watch for signs of viral infections in plants that
have been infested with these insects.
Daily walks through the garden, greenhouse, or commercial
field will alert you to potential insect infestations before they get
out of hand. This is one of the responsibilities of the greenhouse
or farm manager. If plants become heavily infested, physical
methods may be used to remove the insect pest. These methods
can include the application of water or shaking the plant over a
container to catch the insects as they fall. If it is a localized infestation
of annual plants, the affected plants are removed from the
garden. If the plants are perennial, other options to rid the plants
of the pest may be tried before removal. Texts on organic gardening
can be consulted for advice on a particular problem.
|Figure 5.3 Lady beetles, also known as ladybugs,
feed on aphids, which are a common garden pest.
Predatory insects and spiders that feed on destructive insects
are beneficial to the garden (Figure 5.3). Lady beetles (commonly
called ladybugs), parasitic wasps, spiders, lacewings, syrphide
flies, damsel bugs, assassin bugs, and minute pirate bugs are all
beneficials. Beneficial insects can be encouraged to live and eat
in the garden if there is a high diversity of plants and the use of
insecticides is avoided—many insecticides do not discriminate
between the harmful and beneficial insects.
Some species of beneficial insects may be purchased for intentional
release into a field or greenhouse. This is known as biological
control and is a relatively new method. Microbes can also be
purchased for use in biological control. Bacillus thuringiensis
is a commonly used microbial biological control. Experiments
are underway to determine how effective the intentional release
of insects and microbes are for commercial applications. Other
creatures such as birds, toads, reptiles, bats, snakes, and rodents
also eat harmful insects.
Trap crops are plants that are not intended for harvest but
supply habitat for insects and are planted along the perimeter
of a garden. In the foothills of northern Colorado, the wild sunflower
plants and native yucca are good examples of trap crops.
Trap crops can provide a breeding ground for beneficial insects
that feed on pests. This ensures a high population of beneficials
available to protect your crop during the growing season.
Companion crops sometimes work because some plants produce
chemicals that are a deterrent to the insect pest of the crop
you plant next to it. The scent of the companion plant may overwhelm
the scent of the crop that the insect is attracted to such
that the insect is unable to find its food source. Other scents may
be unpleasant enough that the insect stays away from the area.
For example, French marigolds and basil emit a scent that deters
many insect pests and are often planted among vegetable plants
in the garden as companions.
Staggered planting is the strategy of planting a crop earlier
or later in the season than usual to confound the insect pest that
is expecting to find it at a particular time. This works for crops
that are day neutral and do not rely on the day length to initiate
flowering. Tomatoes are one example.
Commercial growers may find that insecticides are necessary
to save a crop in distress, but it is important to identify the under
lying cause of the infestation and try to correct it. Sometimes
the methods used, such as monocropping and amendments that
reduce the tilth of the soil, are the crux of the problem. Insecticides
may require that you obtain a pesticide license before you
can apply them. Since they are toxic, they require a safe place for
storage and may require special disposal methods. They may also
require special equipment to apply. Many insecticides persist in
the soil or contaminate water supplies. Also, insecticides can be
Composting: How to Make Black Gold
Compost, the black crumbly material that remains after decomposition of
plant residues and animal manures, is worth its weight in gold to the organic
or sustainable grower, but it must be of good quality. Compost heaps can
be made directly on the ground or in containers. A source of microbial
inoculation, such as soil or commercially available compost starter, is also
required. A proper mix of carbon and nitrogen in the starting materials is
very important. Straw and dried leaves are high in carbon and are often
combined in layers with grass clippings or kitchen scraps, which are high in
nitrogen. Straw also helps to keep air in the pile, which encourages aerobic
decomposition and prevents the formation of noxious gases. Growers may
also add fresh animal manure or fish scraps to the compost pile as a source
of nitrogen. Fresh manure is not appropriate for direct application to the
garden, as it is too strong and may burn plant roots or spread disease-causing
microbes such as E. coli. Manure sources should be investigated, as some
farmers give their animals high quantities of antibiotics that can inhibit
The composting process takes about six months but is sensitive to cold
temperatures. A correctly built compost pile heats up to more than 60ºC.
This high heat kills pathogens and weed seeds while special microbes
adapted to the high temperature continue the decomposition process. The
pile should be turned regularly to rotate freshly added materials into the
center of the pile and keep it aerated. After the temperature stabilizes and
cools, the compost should ripen prior to addition to the garden. Municipal
compost piles may include sewage sludge, the residue from sewage treatment
facilities, which contains concentrated toxic heavy metals, such as
cadmium, mercury, and lead. There are strict EPA regulations with regard
to how much composted sewage sludge can be applied to the soil. Compost
made with sludge should be avoided by home gardeners.