The Phyllosphere

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 (Bt) 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 expensive.

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 microbial decomposition.

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.