• Organic farmers generally employ relatively non-soluble fertilizer materials, such as compost, manures, plant derived byproducts like cottonseed meal or animal byproducts like feather or blood meals. To insure adequate decomposition and timely nutrient release of these slowly available materials, early spring application is encouraged. Early application also reduces the tendency towards late season growth, which may result in winter damage.
• Surface application of organic fertilizer materials without incorporation is sometimes wasteful of the nitrogen contained in those materials. This is especially true of manures. However, incorporation by tillage could damage the roots of the fruit plants and increase erosion.
• To bypass some of the “problems” associated with slowly available organic materials, some organic fruit farmers choose soluble organic fertilizers such as fish emulsion, soluble fish powder or water soluble blood meal in some cases applying these as a foliar spray. Since these are relatively expensive, the prudent farmer seldom relies exclusively on such materials.
• Most organic fertilization programs focus on supplementing nitrogen as the key element since it is needed in the greatest amount for the crop. One way to determine a proper application rate for an organic fertilizer is to obtain a conventional chemical recommendation for the planting and calculate the approximate amount of an organic fertilizer required to meet it. For instance, if the recommendation for a berry crop is 160 kg of actual nitrogen per acre, a farmer choosing to use cottonseed meal (approximately 7% N) would need to apply about 2000 kg of that material to each acre. Such calculations are simplistic however and may lead to spending more on fertilizer inputs than in necessary. One reason is because biologically healthy soils fix and release greater amounts of nitrogen naturally than those which are not.
• Further more, when making fertilizer calculations based on nitrogen, the farmer needs to credit the estimated contributions made by legume cover crops and or leguminous mulches, where these are used. A cover crop of subterranean clover, properly fertilized and inoculated, can fix from 200 to 1000 kg of nitrogen per acre annually in a living mulch system.
• Basing application rates solely on nitrogen content can cause problems when the fertilizers themselves are imbalanced. Repeated use of poultry manure for example which is very high in phosphate, can lead to pollution problems and a zinc deficiency in the crop. These problems can be averted by regular soil testing and adjusting fertilizer selection and rates accordingly.
• The most reliable means for determining whether fertilization is adequate is to combine field observations with soil and tissue testing. Poor yields, unusual colouration of leaves, and poor plant growth are all clues to a possible nutritional imbalance or deficiency. For example, less than 10 inches annual elongation of the branches of most fruit trees probably indicates a nitrogen deficiency. A corky bark on certain apple varieties may indicate an over availability of manganese in the soil.
• A foliar analysis measures the nutrient content of the leaves and can identify a deficiency or excess well in advance of visible symptoms. It is more helpful than a soil test because the foliar analysis is a measure of what the plant is actually taking up, while soil analysis only measures what is in the soil, which may or may not be available to the plant. Annual foliar analyses generally provide the best guide for adjusting supplementary nitrogen fertilization.

Organic weed management

Research indicates that without some form of weed control in the fruit planting, crop yields and plant vigour will be greatly reduced. In organic farming, weed control is only one goal of a weed management system for perennial fruit crops. A good organic weed management plan should present a minimum erosion risk, provide a “platform” for the movement of farm equipment, not impact adversely on pest management or soil fertility, while minimizing weed competition for water and nutrients. This philosophy has already been demonstrated in discussions regarding three effective weed control tools: cover crops, mulches and soil solarization.

Organic insect and mite pest management

A major distinction between pest management in perennial fruit crops and in annual crops is that crop rotation is not an option (strawberries and to a lesser extent, brambles, are possible exceptions). The long term nature of fruit growing allows for the possible build up of a pest population over time. Conversely, it is also possible for such stable agricultural environments to sustain populations of beneficial organisms.

Plant health and vigour

Though it is sometimes overstated, maintaining the plant in general health and good vigour is important in pest management. For fruit plants, this adage is more applicable to indirect pests (those pests that feed on foliage, stems etc.) than to direct pests (pests that feed on the fruit). For instance, an apparently healthy plum tree may set a good crop of fruit, yet lose it all to the plum. On the other hand, the same tree might suffer significant defoliation by caterpillars early in the season; yet, if it is in good vigour, it can compensate and bounce back quickly still producing a marketable crop that year. There are some cases where general plant health and freedom from stress does impart a form of “resistance” not technically genetic resistance to certain pests. Two examples are apple trees in good vigour actually smothering with sap or casting out invading flathead apple tree borers and plants not suffering drought stress being much less attractive to grasshoppers.

Biological control

Biological control refers to the use of living organisms to control the population of a pest. Examples of beneficial arthropods that have been used to control pests in fruit crops include the predatory mites Phytoseiulus persimilis and Metaseiulus occidentalis, which attack spider mites; lady bird beetles and green lacewings which feed on aphids and Trichogramma wasps, which parasitize the eggs of several pests including codling moth.
Many beneficial insects can be purchased from commercial insectaries and released in fruit plantings. More economical, however is the management of cover crops and adjacent vegetation as insect refugia to attract and sustain native populations of beneficials. As a rule, it appears that beneficial arthropods are not a complete control measure for direct fruit pests at least for commercial farmers who have a low damage threshold for fresh fruit. Usually, additional control measures are required.

Organic and biorational pesticides

Pesticides approved for certified organic production are usually derived from natural sources, break down rapidly in the field and appear to have minimal impact on the environment. Examples include botanical extracts from plants, insect growth regulators, synthetic pheromone treatments that cause mating disruption, soaps, oils, minerals such as sulphur dust and biological pesticides. The term “biorational pesticide” is used to describe pesticides organically acceptable or synthetic, which have minimal impact on beneficial insects and the environment.

Biorational pesticides are considered those providing the least toxic control that can be applied against a pest. Biological pesticides (biopesticides) are both organically acceptable and biorational. Biopesticides differ from biological control in part because they are formulated, labeled and applied like standard pesticides but also because the organisms involved do not reproduce significantly in the field. Biopesticides are highly specific and do not harm humans or beneficial insects. Several biopesticides can be used in fruit pest management. To be effective, they must be used at a specific time in the pest’s development cycle.

The bacterium Bacillus thuringiensis (Bt) is an example of a commonly used biological insecticide. Bt is not as effective against lepidopterous pests that spend their larval stage feeding inside stems, crowns, trunks, or fruit, etc. (e.g., peach tree borer, codling moth, grape root borer, etc.). Other microbial insecticides include Bacillus popilliae for Japanese beetle grubs, a granulosis virus for codling moth, and insect parasitic nematodes for grubs and wireworms.

Botanical insecticides are formulated by extracting toxic compounds from plants that have pesticidal properties. They are naturally occurring, short-lived in the environment and do not leave harmful residues. However, many botanicals are broad spectrum poisons, affecting pests and beneficial organisms alike and are not always the biorational choice. Organic farmers, who are prohibited from using synthetic pesticides, frequently use botanical extracts. Some commonly used plant-derived insecticides are pyrethrum, rotenone, ryania and neem.

Specially formulated soaps that are high in fatty acids are effective against several soft bodied insects including aphids, whiteflies, leafhoppers and spider mites. Insecticidal soap penetrates the insect’s body and disrupts the normal function of cells and their membranes, causing the contents to leak out.

Applying a thin layer of dormant oil to certain woody plants such as fruit trees, grapevines and bushes suppresses pests like leaf rollers, aphids, mites and scales by suffocating over wintering adults and eggs. Dormant oils should be applied prior to bud break and should never be mixed with sulphur because foliage damage may occur. So-called summer oils have a very low viscosity and can be used during the growing season to control aphids and mites without plant damage if label cautions are observed. Insect pheromones are chemicals produced by insects to help them communicate such things as mate availability and sexual receptivity. They are usually specific to a given insect species or genus.

Scientists have learned how to synthesize many of these pheromones and they are widely used for monitoring the emergence or simple presence of crop pests. This information is commonly used to time pesticide applications. New technology also allows pheromones to be used for mating disruption of certain pests. Mating disruption pheromones are available for the oriental fruit moth, codling moth and peach tree borer and grape berry moth.

Organic disease management

General disorders and cultural controls

There are however, some types of disease problems, which are common to almost all temperate zone perennial fruit crops. For instance, because of the relatively soft nature and high sugar content of most mature or nearly mature fruits, fruit rots are common afflictions. The organic farmer can help to minimize the chances of fruit rots by allowing good air circulation and sunlight penetration into the interior plant canopy. Sunlight and circulating air help to dry leaf and fruit surfaces, thereby limiting fungal and bacterial infections. In tree crops, this would mean proper pruning and training techniques. In brambles and berries, reducing plant density helps. In grapes, discouraging rank vine growth and removing leaves that shade fruit clusters is beneficial. For all fruit crops, a site that allows for good air circulation should be chosen.

Another problem common to many fruit crops is root rots and intolerance of poorly drained soils. Most pear rootstocks and some apple rootstocks are relatively tolerant of heavy of poorly drained soils, but even these crops will succumb to persistently waterlogged conditions. Prunus species (peaches, plums, cherries, etc) are very intolerant of poorly drained soils and are generally susceptible to root rotting organisms common in such soils. Other cultural aids in minimizing disease can include such things as maintaining plants in good health and vigour, removal through prunings from the planting site, rouging out of diseased plants, removal of alternate hosts or inoculum sources for the disease organisms.

Organic fungicides and bactericides

Copper and sulphur compounds are the principal fungicides and bactericides used by organic farmers, but they have drawbacks. These materials can cause damage to plants if applied incorrectly. Sulphur is also lethal to some beneficial insects, spiders and mites and can set the stage for further pest problems. Long term use of copper fungicides can also lead to toxic levels of copper in the soil. Furthermore, these fungicides are typically inferior to synthetic alternatives, and have to be used on a protective schedule requiring frequent applications. Research on biofungicides is encouraging. Several formulations of the fungus Trichoderma harzianium are now come to market as a control for grey mold (Botrytis). Other biofungicides now available include a control for powdery mildew in grapes and a protectant against tree wound pathogens.