Report from the Sub-committee on Agriculture

12. Total or partial phasing out of pesticides in forestry

12.1 Wood producing forestry
12.2 Afforestation
12.3 Ornamental greenery
12.4 Furture perspectives
12.5 Conclusions concerning total/partial phasing out of pesticides in forestry

It is generally estimated that a total ban on pesticides in forestry would cause serious problems despite the small quantity used in this sector today. In old woodlands, a fall in profit of 30-40% can be expected, while in the case of moorland forestry, it is doubtful whether any profit at all could be achieved. Production would go down, both quantitatively and qualitatively, and the choice of species of tree would be reduced, which would affect the forests’ value as a recreational amenity (Østergaard et al., 1998). Forestry has been divided into three segments for the purpose of evaluating the consequences:

	Wood-producing forestry
	Afforestation
	Ornamental greenery

12.1 Wood producing forestry

Difficulties in establishing cultures

If the use of pesticides were not permitted in wood-producing forestry, it could be difficult to establish cultures, particularly in heavy soils in Eastern Denmark. It is generally considered that it would take longer for the cultures to become established and that there would be an increased need for replacement planting.

It is also estimated that there would be a change towards more robust species, with spruce, for example, gaining ground at the expense of other species. That would conflict with the desire for a larger proportion of deciduous trees (Østergård et al., 1998).

Another consequence of a ban might be an attempt to make greater use of natural reproduction. This would mean that birch as a pioneer tree species would replace such species as beech, oak and ash. Such a development is not considered desirable.

Today, there are mechanical means of controlling competing weeds. However, the methods in question are not sufficiently robust for use in forests, and the weed closest to the plant cannot be removed in this way. The problem is particularly serious on the heavy clayey soils in Eastern Denmark, where the pressure of weeds can be very heavy, and where machines can only be used with difficulty in moist periods and on hilly land.

It is estimated that weevil would be a problem in connection with the replanting of conifer cultures in light soil. This might prevent regeneration.

12.2 Afforestation

Mechanical weed control

There would probably be rather good possibilities of controlling weeds mechanically on light arable land used for afforestation. In recent years subsoiling (ploughing to a depth of up to 80 cm) has become common practice, particularly in connection with afforestation on light soils, because it considerably reduces the weed population – for five years in the best event. Subsoiling can be problematical with respect to culture-historical traces. However, there are several mechanical methods of controlling weeds after planting. The main problem is weed control around the plants themselves, whereas control between the rows is easy with, for example, inter-row cultivation.

Mechanical weed control is technically feasible today, but is more difficult on hilly land with clayey soil than on lighter soils. In practice, it is often necessary to use pesticides as an emergency solution in situations in which weeds have got out of control.

Insects rarely cause problems in connection with afforestation, so a pesticide ban would cause only limited problems. The exception is the pine weevil, which can occur when afforestation is carried out near established coniferous forests.

12.3 Ornamental greenery

High quality requiremements

Today, production of ornamental greenery and Christmas trees contribute significantly to the economy of many forest properties. Turnover on Christmas trees and ornamental greenery is approximately the same as on timber (DKK 600 million).

The quality requirements for Christmas trees are high. Even minor damage caused by either pests or weeds can thus make a tree or ornamental greenery unsaleable. It is therefore considered that a total pesticide ban would ruin the present profitable production – and particularly the production of Norman fir. Controlling weeds by mowing would increase the cost of production and impair the quality of the trees.

Pests

Pests – particularly chermes in Norman fir – are also a serious problem in some parts of the country, which makes it very uncertain whether the desired quality could be achieved. The uncertainty concerning production of Norman Christmas trees is so great that a large part of the production would probably be discontinued. Just a few, small insect attacks can ruin a whole culture with Christmas trees, so the financial yield would fall considerably. Production of ornamental greenery is an economically accumulating process, so a pest attack in a culture that is 7-8 years old has a far greater economic impact than in the case of an annual agricultural crop.

It is considered that ornamental greenery from Abies nobilis could perfectly well be produced without pesticides, although with a considerable reduction in yield, mainly due to the problem of controlling weeds in the establishment phase.

Alternative methods in forest cultures

There are at present no realistic technical means of controlling weeds in all types of forest cultures in existing forests.

In the case of afforestation, there are good possibilities of using various mechanical methods of the kind developed for mechanical control on farm land.

Mechanical weed-control methods

Mowing machines are already on the market but are considerably more costly than using pesticides. Furthermore, mowing only helps with a couple of the problems caused by weeds, namely, competition for light and damage to cultures. There will still be the risk of frost and the competition for water, which are the main problems caused by weeds (Østergaard et al., 1998). Mowing was used in the old days, when there was also a large number of plants per m2 (40,000/ha), which, in itself, meant better competition with weeds. Today, fewer plants are grown per m².

Another old method used to control weeds was horse-harrowing. Unlike a tractor, a horse can work between the rows and the method also enables harrowing between stumps and stones. For both financial and practical reasons, it is unrealistic to imagine the horse as a solution for the forestry sector in general, although it could perhaps be that on individual properties.

Other methods that have been tried out include soil coverage and the use of livestock. Here, sheep for example have proven an option in coniferous cultures. The drawback with grazing sheep is that one cannot avoid damage from frost.

Alternative methods of controlling pests

In the case of pests, there are as yet no real alternatives to pesticides. Up to the present time, research aimed at the development of alternatives to pesticides has been limited. That also applies to trials of more environment-friendly pesticides (insect soap) and biological control. The main problem with a ban on insecticides would be replanting in moorland and dune plantations, where the seed pod weevil is often encountered.

12.4 Furture perspectives

The sub-committee believes that research and development in the next 10 years are likely to result in the development of improved and more effective methods of mechanical control in fields and in connection with afforestation. In the case of weeds in forest cultures, on the other hand, the possibilities of finding alternative methods of control that can compete with pesticides are deemed to be more limited – also within a 10-year horizon.

In the case of pests, the possibility of developing alternative methods seems limited. In the cultivation of abies nobilis, the producers could perhaps be persuaded to accept a certain level of damage, but pests that attack Norman fir are hardly likely to allow themselves to be kept at a moderate level and level of damage.

12.5 Conclusions concerning total/partial phasing out of pesticides in forestry

Wood-producing forestry

A ban on the use of pesticides would in many cases result in a longer establishment phase, less complete cultures and increased costs for replanting, which would impair the economy of forestry and change the forest scene. It is estimated that one consequence of phasing out pesticides would be a shift away from deciduous trees. Replanting of conifers would give rise to problems with the seed pod weevil in Western Denmark and the other core areas for growing conifers, and deciduous trees would generally suffer problems with grass, which would in turn cause problems with frost and mice. All in all, this would increase the cost of reestablishment and result in a lower rate of growth in the first years of growth.

Afforestation

Unlike replanting in forests, afforestation offers good possibilities of mechanical prevention and control of weeds. A considerable development effort is being made in mechanical control, and a number of practicable machines have been designed for use on easy, flat land. However, the development of machines for difficult, hilly land is going more slowly. If the use of herbicides were banned in the good localities for deciduous trees, one would have to expect the already slow afforestation to be braked still further. In the case of afforestation near existing coniferous forests, there could be problems with weevils. If afforestation took place far from old forests, there would only exceptionally be damage as a consequence of pests.

Ornamental greenery

The quality requirements for Christmas trees are high. Even minor damage caused by either pests or weeds can thus make a tree or ornamental greenery unsaleable. It is therefore considered that a total pesticide ban would ruin the present production of ornamental greenery. Controlling weeds by mowing would increase the cost of production and impair quality.

Pests

Pests – particularly chermes in Norman fir – are also a serious problem in some parts of the country, which makes it very uncertain whether the desired quality could be achieved. The uncertainty concerning production of Norman Christmas trees is so great that a large part of the production would probably be discontinued. Just a few, small insect attacks can ruin a whole culture with Christmas trees, so the financial yield would fall considerably. Production of ornamental greenery is an ongoing investment, so a pest attack in a culture that is 7-8 years old has a far greater economic impact than in the case of an annual agricultural crop.

It is considered that Abies nobilis ornamental greenery could perfectly well be produced without pesticides, although with a considerable reduction in yield, mainly due to the problem of controlling weeds in the establishment phase.

The possibilities of a partial phase-out, which were not specifically considered by the sub-committee, depend on how quickly alternative methods of controlling weeds and pests are developed. A great deal of research covering many alternatives is needed if usable alternatives are to be found. If the spruce aphid is to be controlled without insecticides, research will also be needed to determine whether biological or other methods can be used. The sub-committee does not believe that all the problems relating to alternative control of weeds and pests can be solved within a 10-year period.

Reference

Østergård, K., Hedegaaard, H.M., Søgård Jacobsen, J., Christensen, I.H., Nielsen, F., Dybkjær, T., Rubow, T. (1998): Report on scenarios for phasing out the use of pesticides in private forestry. Report prepared for the Pesticide Committee.