| Forside | | Indhold | | Forrige | | Næste |

Evaluation of Possibilities for Reduced Use of Pesticides in Fruit and Berries

Summary

Production of fruit and berries

Fruit and berry production is extremely intensive and requires a high degree of grower specialisation. Establishment costs are high, typically between DKK 11,000 and 100,000 per ha, and considerable investment in machinery is necessary. Labour requirements are also high, especially when fruit is hand picked for fresh consumption.
Fruit and berry production levels vary from year to year in response to variations in climatic conditions. Prices are determined by international supply. There are no pre-determined minimum prices for fruit and berries and no EU subsidies. As a result, grower earnings vary considerably from year to year.
Fruit and berries are high-quality products, for which common EU standards apply. These quality requirements must be complied with for products to be sold through retail outlets. As a general rule, products must be whole, sound and meet specific size requirements.
According to Statistics Denmark, the total area used for fruit and berry production in 1997 was 7,341 ha distributed among 400 farms. In 1997, the total production of fruit and berries was 32,763 tons representing a value of DKK 190 million.
Total Danish per-capita consumption of fruit and berries was 23.2 kg in 1997. The degree of Danish self-sufficiency was 44.4%.
The total area completely converted to organic fruit and berry cultivation in Denmark was 215 ha in 2000. A further 137 ha is undergoing conversion, of which 71 ha are planted with apple trees. Organic fruit and berry production (including the area under conversion) thus comprises 5% of the total area on which fruit and berries are grown.

Pesticide use

Total sales of pesticides for the period 1996-99 were computed from Danish Environmental Protection Agency figures for quantities of sold active ingredients. Because of the many different uses, the relatively small areas treated and the limited quantities of most pesticides, it was not possible to apportion the quantities sold and thereafter calculate precise application frequencies.
For many insects and diseases only few or solitary pesticides are approved. For some insects and diseases no approved pesticide is available. Many of the products are outdated and, from the point of view of both effectiveness and environmental friendliness, could beneficially be replaced with newer products. However, under the present circumstances, only few new pesticides are being developed for the Danish market.
Treatment indexes for the period 1998-2000 were calculated using grower records of pesticide use. The growers surveyed were large and medium-sized producers, representing all parts of the country. All surveyed pear growers used integrated production practices (IP). Most surveyed apple growers used IP, but a smaller group of growers using conventional cultivation methods was included for comparison purposes.
The treatment index was approximately 11 for strawberry and sour cherry, and approximately 13 for blackcurrant. For blackcurrant and sour cherry the index is 10% less than it was for the period 1994-96. At 15.4, the index for pears remains unaltered. Separate indexes calculated for IP and non-IP apples show that growers who use IP have a lower treatment index (24.5) than growers who do not (27.1). The treatment index for apples has fallen from 25.5 for the period 1994-96, primarily as a result of reduced fungicide application and a lower number of approved products.
The annual cost of applying pesticides varies from DKK 2,230 per ha in sour cherry to DKK 4,750 per ha in apple.

Environmental effect

There is considerable use of pesticides in orchards. During the period 1996–99, 6-15 kg fungicide active ingredient per ha was applied, corresponding to a treatment frequency of 3.8–9.1. In the same period, 0.48-0.84 kg insecticide active ingredient per ha was applied, corresponding to a treatment frequency of 0.9-1.9. There is only limited use of growth retardants in fruit production.
The intense use of pesticides in relation to agricultural crops also entails a relatively higher risk of pesticide loss to the surrounding environment. Orchard trees are often treated with sprayers that give a high degree of drift. However, the risk of drift can be reduced by the presence of windbreaks which generally surround orchards. Drift can also be reduced by using modern sprayers that only apply pesticide when the boom passes a tree and that can collect part of the excess spray.
The loss of pesticides to ground water and surface water is not well documented in Denmark, but the risk of leaching exists to the extent that part of the large quantity of pesticides applied falls to the ground. In undisturbed soil that has not been subjected to intensive soil treatment, it is probable that much of the precipitation falling to the ground will drain away through holes and passageways made by earthworms and mammals. This drain water can rapidly transport pesticide residues over considerable distances.
The large drainage effect on such soil reduces surface run-off. On the other hand, surface run-off is greater from bare soil.
Numerous investigations indicate that there is only a minimal risk of direct fatalities among nesting birds, even in orchards where extremely poisonous insecticides (that are prohibited in Denmark) are used. The reasons for this low mortality are presumably that the birds have collected a large proportion of their diet from outside the treated area, that food sources within the orchard are not as contaminated as could be expected, and that birds loose their appetite after consuming toxic insecticides. The investigations carried out have only surveyed the most common bird species. It is also worth noting that the density of bird pairs at the start of the breeding season is mainly regulated by conditions outside the orchard, i.e. the density of birds in the primary breeding habitat of the species. The investigations carried out do not take into account the fact that the greatest effect of pesticide treatment is on food availability for birds. Several investigations indicate that cultivation methods, including pesticide use, are of great importance for orchard bird life.
It is unfortunate that many of the investigations carried out have not sufficiently taken regional population distribution patterns and food-chain effects into consideration.
Ground flora is generally of great importance for invertebrates and vertebrates. Frequent use of pesticides destroys the natural control of many pests, a factor growers take into account when using integrated production practices by applying as few pesticides as possible and by applying pest-specific pesticides. Investigations of soil microflora indicate that the pesticides presently used in Denmark have no prolonged effects on soil microbiological processes when applied in normal concentrations.

Spraying technique

When using conventional mist sprayers in orchards, a well-established windbreak can reduce drift to neighbouring areas by an average of over 70% throughout the growing season. Tunnel sprayers can reduce the total loss by 25-30%, but cannot be used for all fruit crops. The use of sensor technology reduces loss through drift by 20-30% on average, and can probably be used in all fruit crops. Promising results have yet to be achieved in experiments with electrostatic spray systems in fruit trees.
It is currently possible in several European countries for growers to have their mist sprayers tested. These environmentally protective tests are based on official guidelines that contain a series of specific requirements that must be met by individual mist sprayers. The tests also benefit growers by helping them adjust their sprayers correctly so that the best effect of pesticide application can be achieved with a minimum of negative consequences for the environment and the personnel involved.

Plant extracts and non-synthetic, naturally occurring substances

The ability of plant extracts and other natural substances to control crop pests has been known and exploited for a very long time - for centuries in some cases. However, since the introduction of synthetic compounds, the development and use of plant extracts and natural substances has largely ceased in western countries.
Increased interest in organic cultivation methods during the last few years has once again focused attention on plant extracts and natural substances. Although several of these appear on EU listings of pesticides and other compounds permitted in organic cultivation, they must be approved by the Danish Environmental Protection Agency in accordance with Danish legislation before use in Denmark - an approval that only few substances have attained.
A wide range of substances are known to have some degree of controlling effect on insects and fungi, and in certain cases also weeds. The following substances are those most commonly used, the majority of which can be purchased in various countries, either as brand-name products or as raw materials for the home production of organic pesticides: pyrethrum, nicotine, derris root (rotenone), neem, quassia, Reuneutria sachalinensis (milsana), garlic extract, mineral oils, vegetable oils, essential oils, algae extract, sulphur, copper, sodium bicarbonate, gelatine, sodium silicate and potassium permanganate.
Many of the substances have broad-spectrum effects on insects and are often highly toxic to aquatic organisms while being relatively harmless to warm-blooded animals. Certain substances, nicotine for example, are, however, also highly toxic to higher animals. The majority of the substances are rapidly degraded in the environment, and their effectiveness is therefore short-lived. From the point of view of pest control, this is unfortunate as frequent application is necessary. Conversely, from the point of view of the environment, this is a positive property.
Very little scientific evidence of the effectiveness of plant extracts and non-synthetic substances under field conditions is available.
The following plant extracts and natural substances are currently approved and marketed in Denmark: saponified vegetable oils, paraffin oil, gelatine and sulphur.

Biological and microbiological control of fungal disease

Biological and microbiological control strategies include the following methods: the application of living organisms / microorganisms the application of biological substances that stimulate naturally occurring organisms cultivation practices that stimulate naturally occurring organisms.
Sanitary measures comprising autumn leaf shredding combined with urea and/or antagonist application reduce initial apple scab infections, but will not prevent the spread of disease from infected shoots. Currently, there are no microbiological control agents available, but research in this field is being carried out.
Microbiological control of conidial infection will presumably require many applications throughout the growing season (as is also the case with fungicide treatment) because of the many infection periods.
Pruning shoots that have Gloeosporium pustules in late summer can diminish the source of infectious material. Rot caused by Gloeosporium occurs mostly during fruit storage, but its control can probably be started in the orchard by applying antagonistic organisms that can hinder infection. No such organisms are currently known, however.
There are several products on the world market that can possibly control Monilia laxa under orchard conditions. Research is being carried out, particularly in Spain and the USA, to develop microbiological products to control post-harvest diseases caused by Monilia laxa and Monilia fructigena. Control strategies should concentrate on sanitary measures, including the removal of infected shoots and mummified fruits and if possible the application of antagonistic fungi during flowering to prevent infection.
As is true for apple scab, strategies to control cherry leaf spot should target overwintering stages of the pathogen in leaves, for example by the application of urea and antagonists and by mechanical leaf shredding. Such strategies have the potential to reduce initial infection of young leaves the following spring and thus also to reduce secondary infection. The different methods can also be combined so as to achieve a greater effect. There are currently no commercial products available that contain antagonists to cherry leaf spot. Treatment with 2% urea after leaf fall is already recommended in sour cherry production.
The grey mould pathogen attacks many plant species. There are therefore many inoculum sources and control can be difficult without the use of fungicides. The microbiological control of grey mould is in all probability possible using Trichoderma spp. or Gliocladium spp. It can be expected that repeated applications throughout the growing season are necessary.

Alternative methods - insect pests

In recent years, difficulties have arisen with insects that did not previously present a problem. Formerly, these insects were controlled by broad-spectrum pesticides. However, not many of these broad-spectrum products are still approved. These pests are therefore problematic in both conventional and integrated production. Examples of such pests are pear midge, pear psylla and capsid bugs.
To bring the pest population down to an acceptable level, it is therefore necessary to use alternative methods such as mechanical and biological control. Almost all insect pests have natural enemies, but pest/antagonist relationships are in many cases unknown or only sporadically investigated and described. Nevertheless, knowledge of pest antagonists and their importance is necessary in order to adapt crop rotation and cultivation systems so as to optimise the exploitation of natural enemies.
Plant insect resistance is seldom an "on/off" phenomena. Usually resistance is partial. It can be expressed behaviourally by the pest in question choosing another species or variety to live on because the resistant plant is impossible to colonise or lay eggs on, is repellent, etc. Insect resistance can also be expressed physiologically by the pest not "thriving" on the plant and therefore not doing so much damage. In extreme cases, the insect dies.
Partial insect resistance is very important for pest control as even small differences in resistance between varieties can have significant effects on insect population dynamics. Another form of partial insect resistance is tolerance, where the plant has developed a "system" that makes it possible to continue growth and produce a high yield despite insect attack.

Alternative methods - fungal disease

Disease warning systems for apple scab are commonly used in Denmark and other countries. Various PC programs have been developed to handle data and improve disease risk prediction.
Apple scab infection is correlated to temperature and fungus spores require wet leaves to germinate. Warning systems that predict scab infection have been in use in Danish apple orchards since 1990, and they are a very important tool in integrated production systems.
The systems predict when conditions will be favourable for spore germination and send an alarm. Curative fungicides rather than preventive measures are necessary to control a scab outbreak after spore germination.
A new warning system is currently being developed and tested. The improved program builds on established systems by incorporating additional data on pathogen biology, tree vigour and pesticides and their decomposition. The program is presently being tested in Denmark under controlled experimental conditions and in commercial orchards. The system also has potential for organic growers because it is sensitive enough to allow protective agents to be applied if disease development is closely monitored. Sulphur can be applied in the hours following ascospore release, before conditions favourable to spore germination occur. The new warning system will presumably improve the timing and effectiveness of pesticides used to control apple scab in conventional and organic production. Podem TM, a warning system that predicts the secondary development of apple mildew, has been developed in the UK. The system, which is now commercially available and well described, covers the growing season from leaf burst to termination of shoot growth.
A curative spraying strategy for cherry leaf spot has been developed in Denmark. The strategy is based on a PC warning system modelled on meteorological data in the orchard.
By postponing fungicide application until the system warns of high risk, the number of applications was reduced to 1-4 in the same period. In three out of four years of testing, the high-risk warning system produced satisfactory results. If a special strategy for spraying around the withholding period is prepared then that strategy should be implemented. However, the computer program needs to be made more user-friendly.

Variety resistance

For the last 20 years, improved variety resistance has been one of the main objectives of apple breeding programmes, and many scab-resistant varieties have been produced during the last 10-15 years.
Breeding a new apple variety takes time - up to 20 years can pass before the variety is introduced.
The future of organic apple production depends on being able to grow scab-resistant varieties. Previous breeding efforts are currently coming to fruition and many exciting new varieties are being introduced. Organoleptic quality is constantly being improved by selecting varieties that meet with consumer approval.
At present, two scab-resistant varieties possessing satisfactory organoleptic qualities are recommended on a trial basis.
There are differences between varieties of apple and pear with respect to their natural resistance to scab. The following varieties are currently recommended for organic production:


Klik Click on the picture to view the HTML-version of the table

Trials have also shown which varieties cannot be recommended for organic production. The apple varieties ‘Summerred‘, ‘Mutsu‘, ‘Jonagold‘, ‘Gloster‘, ‘Spartan‘ and ‘Gråsten‘, and the pear variety ‘Clara Frijs‘ are thus characterised as being unsuitable for organic production.
There have been fewer investigations of how to reduce the incidence of disease without using pesticides in sour cherry. Of the two most widespread varieties (‘Stevnsbær‘ and ‘Kelleriis‘), ‘Stevnsbær‘ is the least susceptible to Monilia laxa, and is therefore to be preferred if chemical pesticides are to be avoided. Another important pest in sour cherry is the cherry leaf spot pathogen. The susceptibility of the three most frequently used varieties in Denmark was tested in 1993-95. All three varieties were only slightly or moderately susceptible to the cherry leaf spot pathogen. ‘Kelleriis 16‘ was less susceptible than ‘Skyggemorel‘, while ‘Stevnsbær‘ had intermediate susceptibility.
The most important fungal diseases in blackcurrants are leaf spot, white pine blister rust and powdery mildew. In trials designed to investigate the natural

Grey mould is the most serious disease in strawberry. Traditionally, fields are sprayed approximately three times against the disease. As the pathogen attacks the flowers, and thereafter the fruit, pesticides are applied during flowering. Strawberry varieties that are partially resistant to grey mould are presently available, but no variety possesses total resistance. Currently, the best varieties are ‘Honeoye‘ and ‘Symphony‘.

The apple varieties ‘Rød Ananas‘, ‘Filippa‘, ‘Discovery‘, ‘Guldborg‘ and ‘Ildrød Pigeon‘ are susceptible to attack by fruit tree spider mites, while ‘Aroma‘, ‘Mutsu‘ and ‘Belle de Boskoop‘ are more resistant.

The apple varieties ‘Discovery‘ and ‘Summerred‘ are very susceptible to attack by apple saw fly. Differences in variety susceptibility are to some extent dependent on differences in the degree of synchronisation of flowering with saw fly appearance and egg laying.

The blackcurrant bud gall mite is the most important pest in blackcurrant production. Attempts are being made at present (especially in Scotland) to breed new bud-gall-mite-resistant varieties. A few resistant varieties are already on the market. The varieties ‘Ben Gairn‘ and ‘Ben Hope‘ are currently entering the market, but only became available in Denmark in 2001. This is because private companies invest in the necessary breeding work and therefore have property rights to the new varieties. The companies wish to exploit new varieties themselves, and therefore have no desire to spread them to competing countries.

Cultivation strategies and techniques that reduce the importance of pests, or eliminate them

When establishing permanent fruit crops, the first step in preventing disease and insect attack is to use healthy plant material. If the trees or bushes are infected at planting, effects will often be evident throughout the lifetime of the crop. Several possibilities exist to reduce the incidence of fungal disease. While fungal disease cannot be completely controlled by cultivation practices, the incidence of disease can often be reduced, especially early in the season. If climatic conditions are optimal for a certain disease, it can develop epidemically throughout the season.

Scab survives the winter in leaves shed in autumn. Removal or decomposition of these leaves is therefore important for disease development.

In addition, pruning trees so that they remain small and open reduces the risk of scab infection. Scab can also survive the winter on shoots. To prevent this, it is important that trees do not continue to grow into late autumn. If growth continues after measures to control the disease have ceased, late outbreaks of scab can become established in soft young wood. Scab does not attack mature leaves or wood.

Powdery mildew is a fungal disease that is found especially on shoots. It is often evident as a white powdery fungus growth on shoot tips, but fungus growth and cork spots can also occur on the surface of fruit. To prevent and delay the spread of disease, infected shoot tips can be pruned in newly established orchards. Research has also shown that high rates of mineral nutrition increase the incidence of scab and powdery mildew in apple. In an experiment with scab-resistant apple varieties grown organically with cover crops, resistance degeneration occurred earlier and was more intense in trees grown together with cover crops that provided the trees with most nitrogen. This occurred even though the total nitrogen level in the leaves of both cover-crop treatments was within the optimum range for apple production.

During the last 50 years, the preferred type of tree in apple and pear orchards has changed from large, broad-crowned trees that were widely spaced to small, slender trees that are closely planted.

Closely planted orchards are more productive per unit area and the fruit are of superior quality because of improved light distribution within small-tree canopies. Close planting is also beneficial for production systems with limited pesticide use. The foliage of small trees is less dense, and therefore dries more quickly after rainfall, thus reducing the risk of scab infection. Dwarfing rootstocks produce less tree growth, and trees on some (but not all) rootstocks have a tendency to end growth earlier in the season. The extent and duration of shoot growth is an important factor in tree susceptibility to apple scab infection.

Rot during storage, including that caused by Gloeosporium, is a growing problem in cultivation systems that use limited pesticide control strategies where scab is combated only in the early part of the season or not at all. Experiments with trees of the apple variety ‘Aroma‘ that were not treated with fungicide against storage disease has shown that summer pruning reduced the incidence of Gloeosporium by 75% in 1992 and 35% in 1993 in comparison with ordinary winter pruning. Post-harvest heat treatment of fruit before placing them in cold storage can reduce wastage through a reduced incidence of storage disease fungi. Heat treatment stimulates wax formation and prevents fungus infection during storage by activating enzymes that improve resistance to infection and increase fruit firmness. Heat treating fruit of the variety ‘Aroma‘ reduced the incidence of storage disease by 20-50%.

Mounting nesting boxes for small birds (especially various species of tit) in orchards can be recommended as a means of reducing insect damage. Breeding birds require many insects to feed themselves and their offspring.

In addition, nectar and pollen producing plants can be sown or planted as these attract insect predators that can assist in reducing insect pest populations. The most important means of preventing a wide range of pests in strawberry is to provide a suitable crop rotation. This is for example true for root nematodes and many soil-borne fungi. There is, however, already a long tradition for crop rotation among Danish strawberry growers.

A range of cultivation practices affect the incidence of grey mould to a certain extent, although their importance has yet to be quantified. Mulching with straw or other materials, topping after harvest, good space between individual plants, low weed density and moderate nutrient application are examples of such practices. Finger-harrowing is an effective means of weed control and has recently become common among Scandinavian strawberry growers as an alternative to herbicides. In addition to weed control, harrowing has a preventive effect on grey mould.

The incidence of both grey mould and powdery mildew can be restricted by maintaining good space between plants within rows and by limiting or omitting nitrogen application.

| Forside | | Indhold | | Forrige | | Næste | | Top |