Abstract

A research orchard situated in Canterbury near Ashburton at the Winchmore Research Station is managed to produce commercial grade organic apples as well as providing a resource for research into organic systems. The 4.0ha orchard was established 8 years ago using conventional design and management. After 3 years it was converted from conventional to organic management and has been registered as a "Bio-Gro" production unit.

An interdisciplinary science team has cooperated in a research programme that has focused on biological fruit production techniques. The results from this programme are used to modify and fine tune the existing management system on the orchard, which provides a useful demonstration model for commercial feasibility testing and for technology transfer, through field days and seminars.

This paper reviews results obtained on many facets of management covered in our research programme. It will demonstrate that the vegetative understorey and its management is a key component in organic apple production, influencing tree nutrition and growth, disease levels and pest numbers. At Winchmore, within the constraints of a conventionally established orchard (ie, disease susceptible varieties and close plantings), commercial organic apple production is possible. However, it requires a moderately intensive organic fungicide spray programme to achieve export quality fruit.

Successes and failures are discussed in relation to the techniques evaluated emphasising those methods that can be fully integrated into a successful commercial organic operation.

Introduction

Modern conventional fruit production systems are based on high inputs of pesticides and chemical fertilisers. This type of management is causing concern, both from environmental pollution and food safety aspects. Apples are difficult to grow organically for a number of reasons. The modern varieties that are the basis of our plantings are inherently susceptible to pests and diseases. These plantings are based largely around monoculture designs at high tree density, thereby minimising air movement and creating an environment suitable for rapid host plant spread of diseases and pests.

Prospective organic growers usually have one of two options for development; either convert an existing conventional orchard or, plant up bare ground. The latter option allows more flexibility in terms of creating a more diverse ecosystem by using mixed plantings, planting less intensively and using varieties that have greater disease and pest tolerances than the current varieties. In New Zealand a common practice for growers wishing to produce organic fruit is to convert from existing plantings. This is the more difficult option because of the inherent limitations of a modern conventional orchard. The Winchmore orchard fits this more common scenario and was an important reason for choosing this site as a basis for our research programme.

This paper summarises much of the research that has been carried out at Winchmore with a focus on understorey and interrelated projects.

Methods

The Orchard

The orchard is located at the Winchmore Irrigation Research Station, which is approximately 16km north-west of Ashburton. The orchard was originally established in 1985/86 as a conventional planting for research purposes. Priorities changed after three years conventional operation, and the block then became the focus for an organic apple research programme which facilitated a change to organic management. Since that time the orchard has been managed according to the production standards established by the New Zealand Biological Producers Council for "Bio-Gro" registration.

The orchard is made up of four 1ha blocks. It contains around 2500 trees, comprising Royal Gala, Red Delicious, Braeburn and Fuji. The predominant rootstock is MM106, with MM793 and M9 present to a lesser extent. The day to day orchard operations are performed by an on-site manager. The research station has a meteorological site which provides weather detail necessary for research trials, and for timing strategic orchard management operations, particularly for disease control.

The Research Programme

The research programme uses a science team covering many disciplines who co-operate to investigate both component and systems research. The main objective of the programme is to develop orcharding systems that meet organic standards. The output from this programme also assists conventional growers by demonstrating management techniques that can be substituted to help reduce the use of, and dependence on, synthetic chemicals.

The focus of the research programme has been on the orchard understorey and its management, to determine its impact on pest and predator populations, disease levels and control methods, earthworm populations, irrigation requirements, nutrient cycling and tree productivity.

In December 1989 three separate 1ha orchard blocks were converted from turf grass (Lolium sp.) to either red clover (Trifolium pratense), ryegrass (Lolium perenne) or mixed herb ley (prairie grass (Bromus catharticus), timothy (Phleum pratense), red clover, chicory (Cichorium intybus), sheeps burnet (Sanguisorba minor), sulla (Hedysarum coronarium)). These large single replicate blocks with different understorey herbage treatments provided suitable sites for monitoring disease, pest and predator/parasitoid levels.

To provide detailed information on herbage production, soil nutrient changes and tree growth, a sub-trial was established with each 1ha block having two replicates. Each replicate was situated at either end of the blocks to minimise pest and disease influence on large block treatments. The measurement trees were established five year old varieties of Royal Gala in blocks 1 and 3, and Braeburn in block 2.

A compost treatment was included in July 1990 as a separate treatment used in combination with the herbage understorey (two replicates of each herbage type). This was a proprietary brand of compost called "Bio-blend" made from bark and animal processing wastes. The compost was added in 0.75m wide bands along the treeline at a rate of 5.6 kg/tree (equivalent to 60 kg N/ha).

In addition the sub-trial incorporated a split plot comparison of two sward mowing techniques which were, either mown and returned evenly back to the plot, or mown and transferred as a mulch to the treeline area. Pea straw was added to the treeline area of the mulch treatments each year in July at a rate of one small (15kg) bale/tree. This was done to initiate the mulching process and to help control weeds in the treeline. The mown treatment, which did not have pea straw, had a complete cover of herbage throughout the pathway and treeline.

Results

Understorey Management

The importance of the understorey complex, particularly the floriferous component, has been described as a key component in biological orchard systems (Crowder 1986).

Our work at Winchmore has subsequently shown (Daly and Thomas 1992; Daly 1993) the influence of various perennial herbage species sown as ground cover in an apple orchard and how the cutting management of that understorey sward can influence tree growth, fruit production and tree nutrition, and have implications for pest (Thomas and Burnip 1993) and disease control (Daly 1993) when strategically cut or grazed.

Table 1: Influence of understorey sward type and cutting management on,herbage production, tree growth and fruit yield at Winchmore, 1990-1994.

Further to those results, mixed herb ley has shown to be a most promising ground cover. It has proved to be persistent, to produce well and to have a positive influence on tree growth (Table 1) and nutrition compared to ryegrass and clover.

Red clover performed very well in the first 2-3 years, in terms of growth, but had to be resown after year 3 because of a lack of persistence. It provided the best tree growth and highest tree nitrogen levels in the first 2-3 years (Daly 1993) indicating its potential as a ground cover for young establishing trees that could be resown to mixed ley when it ran out.

Ryegrass, a standard ground cover in conventional orchards has persisted satisfactorily, although it has shown susceptibility to grass grub damage. Ryegrass has been the poorest performing ground cover in terms of tree growth and production. It has however given better fruit colour than some of the other treatments particularly red clover, this may be a low nitrogen or stress induced effect (Saure 1990).

Table 2: Earthworm populations in treeline mulched area versus pathway grassed area at Winchmore, 1991-94.

The mowing management and associated mulching had a significant positive affect on tree production (Table 1) and has to be strongly recommended for use in orcharding systems. The associated benefits of mulching include increased earthworm populations, improved moisture retention and improved nutrition and has been shown in previous publications on this project (in McCarthy, Daly and Burnip 1993).

Earthworms populations have increased enormously since the start of the project particularly in the mulched areas (Table 2). This could be attributed in part to a lack of soil disturbance allowing a natural build up since the initial cultivation and redevelopment, but also possibly to the exclusion of chemical pesticides and fertilisers which can be toxic to earthworms (Edwards and Lofty 1977). There has been some concern expressed over the use of copper on the orchard and the possible negative effects of this element on earthworms. Our soils in the orchard are naturally low in copper and thus far our monitoring has suggested no emerging problem, although we are watchful of copper levels and potential toxicity.

The pathway, the grassed region between tree rows, showed a steady increase from 108 to 517 earthworms per metre square over 4 years (Table 2). The treeline area was mulched intensively in the first year after establishment and may explain the initial very large increase in numbers from 1990 to 1992. Mulching with pea straw was reduced after 1992 and more reliance placed on transfer mulching of fresh green herbage from the pathway (see methods). This may have resulted in the lower population in the treeline from the peak in 1992, nevertheless this population is still very high (4 times higher than the initial level) and the advantage of mulching is still apparent.

Nutrition

There is no indication of falling soil nutrient reserves despite little or no input of fertiliser (small quantities of foliar fish fertiliser) over four years since the trial began (Table 3). Enhanced microbial activity in the absence of chemical fertilisers and pesticides and increasing earthworm activity may be keeping nutrient levels from falling (Lopez-Real 1986).

Table 3: Fertility changes after four years of organic management comparing mowing (clippings returned) versus mulching (clippings transferred) at Winchmore.

There are no apparent nutrition and associated fruit storage problems such as bitterpit, despite no application of calcium to the crop which is a standard procedure in conventional orchards particularly on the variety Braeburn.

Prunings are mulched and retained in the orchard and the utilisation of the herbage understorey by cutting and mulching into the treeline has shown to be an efficient system for maintaining fertility Table 3).

Disease Control

Blackspot (Venturia inaequalis) is the biggest concern in the orchard from a fruit quality aspect. The principle varieties in the orchard, Royal Gala, Braeburn and Red Delicious are all susceptible to blackspot. If blackspot is not controlled extremely well, the total crop can be rejected. Control of this disease is thus a priority.

Most of the disease control work has focussed on blackspot using copper, sulphur and some alternative products such as oil, bentonite clay and slaked lime (Beresford et al. 1991; Beresford and Spink 1993).

Notable features of this work has been that copper (cupric hydroxide) has been shown to be very effective as a protectant fungicide against blackspot. However it requires intensive spraying to maintain a protective cover on the crop. Much lower rates can be used, down to one fifth of the recommended rate (25g a.i./100 litres) and still be effective as a protectant. The work has also shown that by using a low rate of copper in combination with sulphur a degree of synergy occurs, giving better control than those products used in isolation at equivalent rates.

Copper fungicides also cause fruit russet which can have a major effect on fruit appearance and subsequent downgrading. By reducing the rate of copper and taking care over the russet sensitive period (petalfall-early fruitlet stage) russeting can be minimised. Our orchard manager has settled on a low copper/sulphur based fungicide which appears to work well on blackspot as a protectant and also helps control powdery mildew (Podosphaera leucotricha). Another product which is undergoing testing and showing a great deal of promise is slaked lime (Beresford unpublished data). This product is cheap and does not have the same concerns that copper has regarding potential earthworm toxicity.

Powdery mildew is not considered as serious as blackspot because it does not visually affect fruit quality. However, its affect is often under-estimated as it can suppress new growth and tree development quite severely. Colloidal sulphur together with hard pruning of infected apical shoots has been used at Winchmore in the past, however recent results (Beresford and Spink 1993) have shown copper to be more effective than sulphur for controlling powdery mildew. Alternative products are needed to help control this disease more effectively.

Blackspot overwinters on fallen leaf material and then reinfects new leaf growth in the following spring. A trial looking at ways to manage leaf litter showed that mobstocking with sheep during the winter resulted in a 99% removal and disappearance of the leaf litter (Daly 1993). This particular trial also demonstrated that mulch mowing the leaf material encouraged more rapid leaf breakdown and proved a useful alternative to grazing should that option not be available.

Pests

The pest/predator complex has been well monitored and described since the start of the programme, and some interesting changes have occurred (Table 4).

From an initial survey (Burnip and Thomas 1993) it was determined that leafroller, noctuid moths and mites represented the most serious threats to the production of quality fruit at Winchmore. Codling moth, although found in extremely low numbers, was assumed could become a major pest with time.

Two spotted mite (Tetranychus urticae) has, after initially high and damaging levels, settled to a low level presumed to be kept in check by predators (Stethorus sp. and Phytoseiulus persimilis). European red mite (Panonychus ulmi) has increased steadily and although a potentially effective predator is available and has been released into the orchard (Typhlodromus pyri), has failed to persist and adequately control mite populations. Entomologists working at Winchmore suspect that sulphur applications are responsible for this (Burnip pers. comm.).

While lightbrown apple moth (Epiphyas postvittana) was the most abundant leafroller at first, greenheaded leafroller (Planotortrix octo) has become the dominant leafroller species at Winchmore and is the most serious pest at present. No attempts have been made to reduce these leafroller populations, however, as they provide the basis for mating disruption trials (Suckling et al. 1993). The wide plant host range of leafrollers and their high mobility means that mating disruption alone is not usually totally effective, but if supplemented with other techniques such as Bt (Bacillus thuringiensis) applications, may yet give a satisfactory level of control.

Mating disruption trials for codling moth (Cydia pomonella ) has shown to be highly effective particularly at this site where there is very limited potential for immigration of mated female moths.

Mating disruption, alone or in combination with other methods, offers a promising alternative for the control of both codling moth and leafrollers in all apple orchard systems (Suckling et al. 1996, this volume).

Table 4: Trends in insect pests at Winchmore as determined by incidence of fruit damage.

There has been an increasing level of parasitism occurring over time within the orchard. The most notable of these being Dolichogenidea tasmanica on leafrollers. In general, up to about 30% of the leafroller population is being controlled by parasites (Thomas pers. comm.), but is highly variable between seasons.

Thomas and Burnip (1993) found red clover to be a host for leafroller and where red clover is a significant component of an understorey this increases the survival of this pest within the orchard. They concluded that the overwintering population contained on red clover could be very effectively controlled by hard winter grazing with sheep.

Varieties

Varieties that have greater levels of resistance to blackspot in particular are needed to reduce the risk currently associated with commercial organic apple production in Canterbury. Blackspot is the greatest threat to production of high quality grades of fruit. Under an organic system growing varieties which are highly susceptible to black spot, there is often a fine line between keeping the orchard disease free and suffering a disease epidemic. The weather conditions can dominate with a prolonged wet period leaving the crop unprotected and open to blackspot infection. In conventional systems the availability and use of synthetic fungicides with "reachback" or curative activity reduces this risk considerably. Thus there is an urgent need for blackspot resistant varieties in biological systems.

A trial at Winchmore examining up to 40 varieties for disease resistance has shown the potential of a few of these to perform extremely well in an unsprayed situation (no applied biological disease or pest controls). Varieties showing high levels of blackspot resistance are: Prima, Priscilla, Sir Prize, Discovery, Merton Worcester and Laxton’s Fortune (McCarthy 1993). This trial has demonstrated also that in this untreated situation, varieties such as Red Delicious are severely infected with blackspot and often do not produce any marketable fruit.

Commercial Production and Market Outlets

The orchard has served foremost as a research site and for this reason the overall commercial potential and performance of the unit has not been fully demonstrated. A number of research trials has precluded the manager using general application of some biological controls and this has then compromised crop performance. Despite this there has been some encouraging progress towards achieving a reliable packout and producing export quality fruit (Table 5). There has been a general increase in production which reflects the developing maturity of the orchard. Some of the year to year variation is likely to be a biennial bearing effect.

Table 5: Achieving export quality fruit: market outlet, grading % and total volume - Winchmore 1990-94.

The orchard’s fruit has been made available for product development and test marketing and has been well utilised in this respect. Currently our first grade fruit goes to the New Zealand Apple and Pear Marketing Board and they sell both to the local and export markets. Our process grade fruit is made into baby food by a local company ("Only Organic") and marketed both on the domestic and international markets as a canned product.

Conclusions

The programme at Winchmore has made significant contributions towards biological systems research, and in the short duration made considerable progress in developing a viable commercial management system for organic growers.

The science approach used at Winchmore has helped greatly our understanding of the interdependence of various components which make up the whole system, notably the relationships between understorey plants and management on pests, diseases, tree nutrition and soil fertility.

The Winchmore model has shown to be vulnerable to disease infection in particular, an inherent weakness common to modern commercial plantings which invariably have used susceptible varieties. Many of our prospective and practising organic growers operate under these constraints and to change would require a major capital investment. This vulnerability has been overcome to some extent with the progress that has been made on disease management. The work on copper, sulphur, and other alternatives has improved the viability of disease control considerably. Also the recommendation to cut concentrations of copper fungicide by up to 75% must improve the sustainability of this practice. The work needs to continue in this area particularly to finding ‘softer ‘ biologicals as an alternative to copper and to developing resistant varieties.

The monitoring of pest populations and the impact of natural enemies provided essential basic information for understanding this whole complex. The significant progress made on mating disruption of leafroller and codling moth at Winchmore and other research sites in New Zealand will greatly assist growers in their efforts to control these pests.

To conclude, this work must continue and feature as a priority as we strive for management practices that reduce pesticide inputs and improve the overall sustainability of our orchard production systems.

Acknowledgements

Thanks to Neil Alexander our orchard manager for details on management. Thanks also to Dr Howard Wearing and Graham Burnip for their comments on the manuscript.

References

Beresford, R.M. and Spink, M. 1993. Averting the disease scourge in organic apples. Proceedings of Biological Apple Production seminar (July 1993), Lincoln, NZ. ISBNO-478-06803-4, ISSN 1171-9583: 29-33

Beresford, R.M., Elmer, P.A.G., Spink, M., Alexander, R.T. and Daly, M.J. 1991. Fungicides for control of blackspot and powdery mildew in organic apple production systems. Proceedings of the 44th New Zealand Weed and Pest Control Conference : 86-90.

Burnip, G.M. and Thomas, W.P. 1993. Orchard Pests- Monitoring and Management. Proceedings Biological Apple Production seminar (July 1993), Lincoln, NZ.ISBNO-478-06803-4, ISSN 1171-9583: 5-12.

Crowder, R.A. 1986. The orchard understorey - the key to sustained biological production. New Zealand and Southern Hemisphere Horticulture, December 1986: 14.

Daly, M.J. 1993. Understorey management: choice of herbage species and effect on tree performance. Proceedings of Biological Apple Production seminar (July 1993), Lincoln, NZ. ISBNO-478-06803-4, ISSN 1171-9583: 34-41.

Daly, M.J. 1993. Winter management strategies for hastening leaf litter disappearance in an organic apple orchard. Proceedings of Biological Apple Production seminar (July 1993), Lincoln, NZ. ISBNO-478-06803-4, ISSN 1171-9583: 25-28.

Daly, M.J. and Thomas, W.P. 1992. Organic apple production: understorey management, some preliminary findings after the conversion from conventional to organic management. Proceedings of the 9th International Scientific Conference, IFOAM (November 1992), Sao Paulo, Brazil: 2-8.

Edwards, C.A. and Lofty, J.R. 1977. Biology of earthworms. Chapman and Hall, London.

Lopez-Real, J.M. 1986. Sustainable Agriculture: the microbial potential - the microbiologists challenge. pp. 1-8 in Lopez-Real, J.M. and Hodges, A.B. (eds) The role of microorganisms in a Sustainable Agriculture. Academic Publishers, London.

McCarthy, T.P., Daly, M.J. and Burnip, G.M. 1993. (eds). Proceedings of Biological Apple Production seminar (July 1993), Lincoln, NZ. ISBNO-478-06803-4, ISSN 1171-9583, 78pp.

Saure, M. 1990. External control of anthocyanin formation in apple. Scientia Horticulturae, 42: 181-218.

Suckling, D.M. 1993. Small scale trials of sex pheromones for mating disruption of a native leafroller. Proceedings of Biological Apple Production seminar (July 1993), Lincoln, NZ. ISBNO-478-06803-4, ISSN 1171-9583: 20-24.

Thomas, W.P. and Burnip, G.M. 1993. Lepidopterus insect pests and beneficials - the influence of understorey. Proceedings Biological Apple Production seminar (July 1993), Lincoln, NZ.ISBNO-478-06803-4, ISSN 1171-9583: 13-19.