|ORGANIC FARMING :: Horticulture Crops :: Fruit Crops|
Organic Farming - Introduction
Organic Cultivation of Fruits
Organic fruit production essentially excludes the use of many inputs associated with modern farming, most notably synthetic pesticides and fertilizers. To the maximum extent possible, organic farming systems rely upon crop rotations, crop residues, animal manures, legumes, green manures, off-farm organic wastes, mechanical cultivation, mineral- bearing rock powders and biological pest control. These components maintain soil productivity and tilth, supply plant nutrients and help to control insects, weeds and other pests.
All factors regarding site suitability for conventional fruit plantings (air and water drainage, etc.) apply even more and so to organic operations. While conventional farmers may fall back on chemical fertilizers and pesticides to compensate for poor site decisions, organic farmers largely give up such luxuries. The presence of certain weeds and forage species are also of particular concern to the organic farmer. Bermudagrass, Johnsongrass and several other species can be quite problematic to farmers and are difficult to control through nonchemical means.
Growing fruit crops offers an advantage to farmers interested in sustainable agriculture. Because fruit plantings are perennial, the soil may not require additional tillage or cultivation beyond that needed at establishment, thereby minimizing soil erosion. Because the potential for erosion is low, hillsides and other sites unsuitable for tillage agriculture can safely and successfully produce fruit crops.
Environmental constraints (climate, presence of certain pests and diseases, suitable soils, etc.) can greatly impact the suitability of a given site or even a bioregion for organic production of a given fruit crop. Generally speaking, some perennial fruits are easier to grow organically than others. The small fruits (berries) for example, seem easier to grow organically than the tree fruits in almost all locations. Lastly, successful organic fruit growing may depend largely on whether the venture is for home production or for commercial sales.
Attention to the details of site preparation can go a long way towards reducing weed and disease problems and assuring a vital planting through soil improvement.
In general, fruit crops do not require highly fertile soils for good production. In fact, highly fertile soils, rich in nitrogen, can promote too much vegetative growth at the expense of fruiting. A nutritionally balanced soil, proper oil pH and plentiful amounts of organic matter are the fundamentals of an organic fertility management plan for fruits. Preplant soil improvement for organic fruit plantings is typically accomplished through some combination of cover cropping/green manuring and the use of imported materials, which may include manures, compost, rock powders and organic wastes.
Of particular importance at this stage is the application of required amounts of lime or sulphur. The need for lime or sulphur is dependent on the crop to be grown and the results of soil testing. Adjusting the oil pH with lime (to raise the pH) or sulphur (to lower pH) is much more easily done before planting. Most fruit plants perform best around pH 6.5, although they tolerate a pH range between 5.5 and 7.2. Blueberries are an exception. They require an acid oil-ideally pH 4.8 to 5.2 soil testing should also be used to guide applications of manures and other rock powders to avoid nutrient imbalances.
Cover crops and green manures not only contribute to soil fertility but also can become part of an active plan for pre-plant weed suppression as smother crops. The basic strategy begins with ploughing under sod or other existing vegetation, planting a cover crop to suppress weed growth, tilling under the cover crop and setting plants. Sometimes several rotations of cover crops are used before setting plants.
Selection of specific cover crops and their management varies with location, depending on such factors as seasonal rainfall, soil type, soil erosion potential, available equipment and seed cost. For example, crotalaria probably performed less effectively than sesbania at different centre because it is poorly adapted to low, wet soils. Some other warm season cover crops that might be considered include aggressive maize varieties and forage soybean varieties.
Crops such as berries (strawberries) are often grown on raised beds to encourage drainage and reduce root rot disease problems.
Another technique for site preparation is soil solarization. The process involves placing transparent polyethylene plastic on moist soil during the hot summer months to increase soil temperatures to levels lethal to many pests.
Orchard Floor Management and Mulching
The floor or inter row areas of perennial fruit plantings may be managed in a variety of ways, ranging from clean cultivation to various combinations of cover crops and organic mulches. In terms of controlling erosion at least, a system that results in full or close-to-full ground coverage is best. If the decision is made to plant a between row ground cover, it should consist of a species adapted to the region and to the fruit farmer’s management plan. Where adapted, orchard grass and other cool season grasses are often recommended because they go dormant during the heat of the summer, thereby minimizing competition with the fruit crop for water. With proper fertility management these grasses may also provide plentiful material for mulch. Many warm season legumes are deep rooted and compete with the trees for water, they should not be allowed to grow under the tree canopy. However, legumes and the mulch made from leguminous ground covers can provide significant nitrogen to fruit trees or vines. Furthermore, even though they complete with the fruit plants for water, legumes (like the grasses) increase the water permeability of the soil. Increasing the organic matter content of the soil also increases the soil’s moisture retentiveness.
Subterranean clover reseeds itself in early summer and dies back during hottest part of the growing season leaving a relatively thick, weed suppressive duff or mulch. This system has shown applicability in apple and peach orchards and for a variety of orchard crops. Subterranean clover is not adapted to climates where winter temperatures regularly drop below 0 °F.
Many researchers have also investigated the relationship between orchard floor management and pest control. In some place apple orchards peach orchards, a diverse mix of cover crop spices provided habitat and food for an array of beneficial organisms, resulting in a decrease of orchard pests.
Mustards, buckwheat, dwarf sorghum and various members of the Umbelliferae and Compositae families support substantial numbers of beneficial insects without attracting as many pests.
After a planting is established, mulching with organic materials such as straw, leaves or sawdust can provide significant weed suppression. If applied thickly enough or supplemented with sheets of paper or cardboard as the bottom layer, complete suppression might be achieved. Application of mulch varies somewhat by crop. In strawberries for instance, mulch might cover entire aisles between rows or only be placed next to the bed to inhibit encroachment by creeping weeds. In vineyards and orchards, mulch might be placed only under individual trees or vines or along the entire row, ideally extending to the drip line.
Generally, mulch should be kept well away from the trunk to reduce damage from voles. This is especially important in winter. Keeping the mulch 8-12 inches away from the trunk also reduces the likelihood of crown rot and other diseases in susceptible species most notably applies on certain rootstocks. In mulberries, sawdust mulch is commonly spread along the entire row with extra sawdust mounded around the canes, often to a depth of 8 or more inches. In addition to controlling weeds, mulching with organic materials improves the soil by enhancing soil aggregation and water availability.
Because the plants are perennial and represent a considerable investment in both time and money, it is important to start the fruit planting with the optimum varieties for location and markets.
Good information on varietal selection is available from Cooperative Extension, nurseries and local commercial farmers. It is also important to obtain clean planting stock. Buying from reputable nurseries that provide stock certified by certifying inspectors to be free of diseases and insect pests is recommended.
Genetic resistance refers to inheritable traits in the plants that inhibit disease and pest damage. Choosing genetically resistant cultivars is a very important control measure for organic farmers especially with regard to disease management. In some cases, such as bacterial spot in peaches, cultivar resistance is the best or only control.
Aphid resistant berries, Phylloxera resistant grape rootstocks, wooly aphid resistant apple rootstocks, mite resistant strawberry cultivars, and nematode resistant peach rootstocks are available. As important as this resistance is there is no cultivar of any fruit species with multiple insect pest resistance; therefore, means other than resistance will most likely have to be employed to protect fruit plant from a complex of several pest species.
Organic fertilization practices
Harvested fruit, being largely water, removes relatively few nutrients from the soil, compared to other crops. Therefore, a significant amount of the fertility needs of fruit crops can be met through cover crop management and organic mulches in systems which use them and by the application of lime and other slow release rock powders at the preplant stage. Still, supplementary fertilization is often required for optimum growth and production.
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 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.
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.
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