SWEEP Results

Introduction

Weed management under SWEEP guidelines aims at enabling effective weed control on pavements while reducing herbicide runoff to acceptable levels, all against reasonable costs. The method has been tested from 2002 to 2004 in various residential areas. An acceptable weed level in these areas was set as precondition. This was defined as a maxi­mum of 25% growth of the joints between the paving stones and no weed higher than 2-3 cm.

On average, herbicides were applied two times per season at those places where herbicide use was permitted under DOB guidelines. Roundup^® Evolution (a.i. glyphosate) was the main product used through application by means of selective spraying techniques. Whenever necessary, brushing, sweeping, burning or mowing were carried out at places where herbicide use was not permitted. The weed picture was reasonable to good in each season, also under high weed pressure as in the wet summer of 2004.

Application of the SWEEP guidelines resulted in the ecological threshold concentration for glyphosate in surface water not being exceeded. These measurements were conducted at those points at which rain water gets into the surface water via the sewage system. In some samples, the glyphosate concentration was slightly higher than the stricter drinking ­water criterion but this surface water was not intended for drinking water ­pro­duction. Still, this resulted in sharpening of the SWEEP guidelines. The following additional condition has been included in the SWEEP system: apply no herbicides on pavements that runoff to a point in flowing surface water which through an open connection is situated 10 km or less upstream from a intake point for drinking water production.

The SWEEP system aims at a maximum reduction of herbicide use. The upper limit for glyphosate is 360 g active substance per hectare. Registration by municipalities, however, showed that exceedance of this level could not be avoided in all cases. Use in the tested areas ranged from 100 to 600 g active substance per hectare. Glyphosate runoff, however, was a factor 10 lower than runoff under standard chemical weed control.

Information of the participating municipalities showed that the additional costs of weed control according to the SWEEP method ranged from hardly any additional costs to a maximum cost increase of 30% in comparison with standard chemical control. This is in particular caused by the use of different techniques on places with a high emission risk (burning, brushing etc.) and fewer days on which work can be done. Chemical-free area management was chosen in a single case; here the costs amounted to € 0.15 m^-2.

Weed control on pavements under SWEEP guidelines results in a considerable reduction of herbicide runoff to surface water. If runoff occurs, this is especially the case in the first precipitation ­peri­od after application of glyphosate. A good forecast of the precipitation chance during and after weed control is therefore important to reduce this risk as much as possible. In practice, a decision about the permissibility of applying chemical pesticides on a particular day is taken on the basis of an actual weather forecast. Experience with SWEEP shows that effective weed control is possible without exceedance of the water quality criteria. This means that in the long term risks regarding drinking water pro­duction will also decrease.

Field testing shows that the SWEEP method enables effective weed control with environmental effects and costs remaining below acceptable levels. The most important results of weed management under SWEEP have been summarised in the table below.

 ¹⁾ MTR is the (ecologically) maximum tolerable risk level. It is the concentration criterion above which harmful effects on fish, plants or insects in surface water may be expected.
²⁾ Cause of additional costs in comparison with standard chemical: use of other techniques and fewer days on which work can be carried out. Some municipalities stated that costs had hardly increased. Costs are given without internal costs.