Pesticides Research, 97 – Autonomous Weeder for Christmas Trees – Basic Development and Tests

Autonomous Weeder for Christmas Trees – Basic Development and Tests

1 Introduction

Christmas trees occupy a small fraction of the cultivated land, but count for a relatively high input of chemicals per area (Christensen 2003). This may cause problems of leaching of both pesticides and nutrient (Pedersen et al. 2002). Another negative consequence is low flora diversity in plantations treated in this way. These problems place Christmas tree plantations as a high priority area for alternative weeding methods.

Some growers already use mechanical weeding implements (Keller, 1997), but these are costly to use because of the high investment, low capacity and high labour requirement. These weeding implements are able to remove weeds between the rows, and a few of them have tools that can remove weeds in the intra-row areas, where weeding is most important. The generally applied strategy of mechanical weeding is the same as for spraying, i.e. to remove all weeds. Therefore, mechanical weeding in the form of tillage also causes problems of leaching and low biodiversity.

In latter years several traditionally used persistent soil weed herbicides have been either forbidden or re-evaluated and some producers have started to use screened spraying systems. Weed control by grazing sheep (Theilby 1997) and also soil covering with different materials (Kjærbølling 1997) are possibilities that have been tried, but both methods turned out to be too expensive. Therefore, Christmas trees are still a high priority area for development of alternative weeding methods.

In a preliminary feasibility study Have et al. 2002 concluded that use of small, autonomous weeders in Christmas trees would not only be technically feasible but also friendlier to the environment. In addition such weeders could be competitive to ordinary mechanical row weeders in a shorter term. The study also investigated the requirements of weed control, gave an overview of the state of the art of autonomous field vehicle technology and defined the technical requirements of a weeder. It also considered various vehicle concepts and system architectures.

The purpose of the present project was to develop and test such a small, autonomous Christmas tree weeder (ACW), including:

Identification of a suitable, existing motorized vehicle platform
Modification of this vehicle by addition of a special rotor cutter mechanism, actuators, sensors and a control computer with accessories
Development of a feasible control system that on basis of the sensor inputs can operate the machine autonomously for weeding in Christmas trees
Test the machine in various practical conditions.