| Front page | | Contents | | Previous | | Next |

Cleaner Technology Projects in Denmark 1997

Methods on Reduced Use of Chemicals in Forests

Metoder til reduceret kemikalieanvendelse i skov
Miljørapport nr. 348, 1997, Miljøstyrelsen

In general, the use of pesticides in the forestry is modest, but in the 30-40,000 ha where Christmas trees and greenery are produced, the consumption of herbicides as well as insecticides has been very large and consequent throughout approx. twenty-five years. A number of late discovered environmental problems are the consequence.

It is an obvious thought to reduce herbicides by replacing total spraying of the full crop area with a partial control of weeds which grow in close vicinity to the crop, and which have the greatest influence on its growth. In this way the remaining part of the vegetation is spared to benefiting the wild fauna, the aesthetic element of the landscape, the microclimate, reduced nitrate leaching, etc.

Technically, the simplest method of partial chemical weed control is to band spray over the plant rows, and this practise has been followed in the present investigation of the production and vegetative consequences of partial weed control (section 2), and at the estimation of the implemental possibilities under various terrain conditions (section 3).

In trials with the three species Abies nordmanniana, Abies procera and Fagus silvatica, the production conditions are compared with: 1) full treatment (100%), 2) wide band spraying (67%), 3) narrow band spraying (33%), and 4) untreated for control (0%). The latter is totally unrealistic in practice.

The trials show that for the first two years after planting it is possible to reduce the annual use of the current soil herbicides by one third compared to the normal consumption without noticeable losses with regards to growth and prosperity of the plantation.

Furthermore, the trials show that band spraying cannot "stand alone", since the development of weeds in the space between the rows gradually prevails and the weeds become too high. Supplementary measures must be carried out with an interval of one to two years.

In this case one could imagine:

1. A full spraying with low dosages of leaf herbicides, which do not need to have a mortal effect on the weeds.
     
2. Mechanical measures, such as harrowing, mowing/cutting, or rolling are also possibilities.
     
3. Establishment of cover crops in the space between the bands (e.g. low species of white clover) must be assumed to have a weed controlling effect, but could imply an increased risk of frostbite (spring night frost) and they are of course - as the weed plants – a water competitor.

Use of band spraying in practise will cause an increased labour force in the cleaning area. The possible savings on the herbicide expenditures can hardly compensate for the increased costs of special spraying equipment, supplementary measures and the increased work performance. Therefore, the motivation must come from the agriculturist’s raising concern for environmental problems and on the background of the possibilities this project has shown.

The work concerning reduction of the pesticide use by means of spraying technology development has included three subjects: 1) Development of spraying technique, 2) technique for screened spraying in forestry and 3) implementation of new technology for accurate application of pesticides.

Band spraying is technically possible in forestry by use of knapsack sprayers. PTO-driven band sprayers can be used in cultures on former agriculture land, but heavy demands are made on the accuracy of the planting and on maintenance of the spraying equipment. To most producers the extra costs of band spraying will exceed the savings on the chemicals.

With several growers a combination of mechanical cleaning and band spraying is used with good results. In this way both a reduction of the use of chemicals and a more gentle treatment is obtained than by mechanical treatment alone, but the positive effect of the vegetation as regards leaching, coverage and shelter of flora and fauna is lost. An economic gain will not be obtained by a combination of band spraying and mechanical cleaning.

Various pieces of equipment have been developed for screened application of herbicides in cultures of Christmas trees, and the method must be characterised as implemented in practice. However, a great deal of effort is still carried out to further develop the equipment. A tool for treatment of several rows at the same time is wanted. Several growers are working to meet this requirement. Drive dependent dosage by means of the simple Hardimatic equipment is very common in practice. On the other hand, only very little interest in, and need for, advanced information technological steering systems for forestry sprayers are noted.

The project has contributed to acknowledgement and increased knowledge of possibilities to reduce the use of environmentally harmful weed-control agents in practice.

Author/ institution

Thomas Rubow and Lars Kjærbølling
Statens Planteavlsforsøg

This report is subsidised by the National Council for Recycling and Cleaner Production

ISSN no. 0105-3094
ISBN no. 87-7810-725-3

| Front page | | Contents | | Previous | | Next | | Top |