Optimization of the spray application technology in bay laurel (Laurus nobilis)

Bay laurel is an evergreen, commercially grown and expensive ornamental pot plant, which is susceptible to different pests like aphids, scale and lerp insects, thrips, caterpillars of codling moth and sooty moulds. Recently, caterpillars of the Mediterranean carnation leafroller (Cacoecimorpha pronubana) cause more and more problems. These pests can lead to important financial losses for the growers. During summer the individual pot plants are placed on a field-container in a fairly dense configuration. Crop protection is traditionally done by moving with a spray lance between the rows of pot plants and treating each individual plant from bottom to top. Good penetration is clearly an important advantages of this spray technique but it is very time-consuming, unhealthy and laborious. Some other growers use a 'spray platform' on a high-clearance tractor. Plants sprayed from this platform are exclusively approached from above resulting in an inferior spray deposition on the lower parts of the plants. To overcome the disadvantages of both available techniques, the potential of an automated tunnel sprayer was investigated. Five different nozzle types were evaluated under laboratory conditions i.e. hollow cone, standard flat fan, air inclusion flat fan, deflector flat fan and twin air inclusion flat fan at spray pressures varying from 3.0 to 7.0 bar depending on the type of nozzle. For each nozzle type, three nozzle sizes were included in the experiments which resulted in 15 different spray application techniques. All experiments were done at a speed of 2.5 km h^-1. This resulted in three different application volumes: 2450, 4900 and 7300 L ha^-1. After optimizing the nozzle configuration (distance and orientation) using water-sensitive paper, deposition tests with five different mineral chelates as tracer elements were performed. Filter papers were used as collectors at 20 different positions to measure spray deposition, distribution and penetration in the canopy. For each application technique, four plants were selected as repetitions. Irrespective of the nozzle type and spray pressure, 4900 l x ha(-1) was found to be the optimal spray volume with deposition rates varying from about 50 to 70% depending on the nozzle type. The best results were found for the hollow cone, the standard flat fan and the air inclusion flat fan nozzles. Nozzle type and pressure and the corresponding droplet characteristics were closely related with the penetration and deposition results. With this automated tunnel system, it is possible to obtain a good spray result in combination with an increase in the productivity and a reduction in operator exposure.