Variable rate application (VRA) of pesticides based on measured spatial variation in crop biomass is possible with currently available crop reflection sensors (remote and proximity), GNSS technology and modern field sprayers. VRA has the potential to contribute to a more sustainable use of pesticide. Dose rates are optimized based on local requirements at a scale of about 5-50 m², leading to less adverse side effects, less costs and higher yields. In the longer term, we will also see individual plant treatment (scale less than 1m²).

WUR-PRI has developed with some partners a VRA system for leaf dessicants (potato haulm killing herbicides) in potato. A central element of the system is the model (dosing algorithms) that relate biomass parameters to minimum effective doses of the dessicants, such as the a.i. diquat-dibromide, glufosinate, carfentrazone-ethyl. A first prototype of a proximity sensor (Yara N-Sensor) in combination with the dosing algorithms and a Hardi injection sprayer was successfully tested in ware potatoes in 2006. In next years, other types of sprayers in combination with other types of proximity (e.g. GreenSeeker and Crop Circle) and remote (satellite and UAS mounted) sensors systems were tested. The R&D resulted in a situation that farmers have now access to a pallet of options to acquire spatial information on crop biomass on their fields. With the Dutch satellite images database, farmers have access to biomass data on a scale of 2 by 2 m. If data are obtained from UAS mounted cameras, the scale is even smaller.

The VRA system has been tested in on farm research over six years in several North West European countries. Data from observations in this on farm research show a reduction in potato haulm killing herbicides of more than 30 % for the VRA system compared to standard practice. The actual reduction is e.g. determined by resolution of sensor, patchyness of the field and width of (the section) of the spray boom. Following up on the success of the VRA potato haulm killing system, new biomass dependent VRA systems for fungicides in e.g. potatoes, strawberries and orchards are being developed at Wageningen UR.