Spray application volume test in apple and pear orchards in Catalonia (Spain) and Variable Rate Technology for dose adjustment.

The adjustment of spray application conditions is still an issue in spray applications in fruit crops. Many fruit varieties are found in apple and pear orchards, that can be in different development stages and grown in a wide range of training systems. The active ingredient of a pesticide preparation can be delivered using different volume application rates (VAR), which if not well adjusted to each orchard can cause a diminution of the application efficiency. The objective of the work was to decide the best VAR in two apple varieties (Golden and Red Chief) and two pear varieties (Blanquilla and Conference). During two growing seasons, three VAR (400, 800 and 1600 l/ha) were tested in different orchards. Spraying parameters were kept as similar as possible (sprayer, forward speed, droplet size, air volume rate, weather conditions, etc.) so that the differences were mainly caused by the tested VAR. Depending on the results, there was a possibility to design and test a variable rate (VR) sprayer prototype able to deliver an specific flow rate according to the volume of vegetation detected by ultrasonic sensors. According to the results, no clear trends were found between the three different VAR, although it seems that the lowest VAR could be more suitable for early season spraying, whereas in full stage applications the highest VAR seemed more adequate. The fact that the same droplet size and a last generation sprayer were always used can explain why no differences between the corresponding spray deposits were found. The results found led us to develop and validate the VR prototype turning out into very optimistic results on dose adjustment in real-time.