This section notes the options for the main maintenance operations in orchards, apart from pruning and those associated with establishment: grass management, control of pests and diseases, mulching and fertilization. The actual operations appropriate in any one orchard are very dependent on the context.

 Grass

Trees are generally sensitive to competition from grass for water and nutrients, especially for soil nitrogen (N). If trees are excessively vigorous and unfruitful the soil is likely to be high in N, and a sward may beneficially check growth and encourage cropping. A sward also contributes organic matter and may alleviate some mineral deficiency symptoms (particularly potassium and iron), tends to delay the time of blossoming, improves fruit colour, reduces pre-harvest drop and provides a good working surface. Apples from grassed orchards also store relatively well. Many of these effects are due to the moderation of soil and plant N and to the growth of the tree’s roots into the surface layers of the soil beneath the sward (ADAS/MAFF, 1972).

Under different circumstances, the competition from a sward may be so high as to be detrimental to growth and cropping. In this case, competition can be restricted by irrigation or N fertilization (provided the grass doesn't preferentially benefit). Grass competition is eliminated altogether in intensively-managed orchards by keeping the rows bare of vegetation with herbicide. Freedom from weeds is also achieved by cultivation, although this can damage surface roots, or by mulching.

Herbaceous ground vegetation is sometimes managed sympathetically for wildlife by cutting just once or twice a year, allowing diverse herbs to flower and set seed but preventing woody vegetation from establishing itself. Only the most vigorous of trees are capable of withstanding this much competition. Short grass at harvest is helpful in the collection of windfalls, whether desired for a processed end use (such as cider) or to be composted for the sake of good hygiene.

Options for the control of grass/weeds, diseases and pests

Herbicides and pesticides available to the uncertificated user (ie. available in the retail trade) have become increasingly restricted in recent years, as have the sprays approved for organic culture such as the traditional sulphur and copper-based preparations and derris (rotenone).    

Grass/weed control

Within the row (if not grassed), the options are: Hand-weeding, organic mulches, plastic sheet mulches, mechanical cultivation, sowing/harvest of cover crop, herbicide (eg. glyphosate, or Roundup) or some mixture of these.

Between rows, which are grassed even in intensively managed orchards, and within the row (if grassed): Mowing, the use of mechanical hand tools such as strimmers (for which the base of the tree may have to be protected), scything or grazing. Sheep are likely to browse fruit tree foliage if within reach, up to height 1.5m from ground level (Hodge & Pepper, 1998).

Disease control

In low-input management, the use of resistant varieties and good hygiene including winter pruning, the raking and destruction of scabby leaves and the removal of any incidence of disease as soon as it appears during the growing season.

Pest control

Recommendations for organic culture (Bevan & Knight, 2001) include the dedication of say 10% of the orchard area to habitats suitable for predatory insects, birds (that are also predators of insects) and alternative prey (to encourage predator populations to increase). These include floral strips, hedgerows, shelterbelts, areas of uncut nettle, artificial shelters for predatory insects such as earwigs, bird and bat boxes, and accessible water (for birds). 

Grease bands (winter moth), pheremone and other traps (codling moth), biological control of caterpillars with Bacillus thuringiensis, good hygiene including keeping the base of the tree bare of vegetation (to reduce shelter for overwintering pupae) and the destruction of maggoty fruit. These options are discussed in more detail in Bevan & Knight (2001) and Soil Association (2001).

Mulches

 Mulches consist of material put on the surface of the soil, variously to suppress vegetation, provide nutrients or organic matter, allow better penetration of rain and slow the loss of soil moisture. They may be organic (compost, manure, wood chip, straw etc.) or inorganic (such as plastic sheeting). They are relatively valuable for conserving soil moisture on soils with low water reserves and in areas of low rainfall. On wet sites they may retain too much water, leading to poor aeration, waterlogging or compaction. Mulches also insulate the soil so that they slow the radiation of heat from bare soil to the air above on cold nights, increasing the risk of frost damage to blossom on susceptible sites.

Organic mulches are variable in their nutrient content. They can be so low in nutrients (especially woody ones) that they temporarily deplete the soil as they decompose.

 Fertilizer

 The main nutrients of plants are nitrogen (N), phosphorus (P) and potassium (K). Soil N is mainly present in, and released from, soil organic matter. Other nutrients including P and K are also released gradually from decomposing organic matter. Soils that are biologically active generally have high fertility.

The most reliable way of determining nutrient requirements is by soil and leaf analysis. In their absence mineral fertilizers have to be applied with caution. They can be physically damaging to plant roots if too concentrated and can cause (as well as cure) mineral deficiencies. For example, too much K can lead to a deficiency of magnesium (Mg) or calcium (Ca), resulting in the disorder ‘bitter pit’ in susceptible varieties. In many situations it is best to rely primarily on the natural fertility of the site, supplemented with an N:P:K fertilizer at planting or according to the later growth of the trees.

References

 A.D.A.S./M.A.F.F. (1972). Apples. Bulletin 207. H.M.S.O. London.

Bevan, J. and Knight, S. (2001). Organic apple production: Pest and disease management. Henry Doubleday Research Association, Ryton Organic Gardens, Coventry CV8 3LG. Emmerson Press, Kenilworth. ISBN 0 905343 31 X.

Hodge, S. and Pepper, H. (1998). The prevention of mammal damage to trees in woodland. Practice Note FCPN 3 The Forestry Authority, 231 Corstorphine Road, Edinburgh, EH12 7AT. ISBN 0-85538-373-9.

Soil Association (2001). Guidelines for the production of organic apples and pears in the United Kingdom. By the Organic Top Fruit Group, Soil Association, South Plaza, Marlborough Street, Bristol BS1 3NX. Downloadable from: http://www.soilassociation.org/web/sa/saweb.nsf/2a64bf6e719c195980256efc00560910/e25e97750de2391d8025733d0032f7c1!OpenDocument