Field tests of a prototype microwave-based weed killer machine were conducted on Abutilon theophrasti, Panicum miliaceum, lucerne and oilseed rape pure stands. The approach can be considered a thermal weed control method, the microwave radiation causing dielectric heating of plant tissue water that eventually kills the plant. The method could overcome the limitations of other thermal methods, such as fire risk with flaming or the heavy loads required for hot water treatments. Species were effectively controlled by microwave irradiation, but their sensitivity and the evolution of damage symptoms over time differed. Lucerne showed no sigmoidal response and was the least affected by the treatment, while a log-logistic curve expressed the doseresponse relationships of the other species quite well. The estimated microwave dose for a 90% dry weight reduction ranged from 1015 kJ m )2 in A. theophrasti to 3433 kJ m )2 in P. miliaceum. Energy cost evaluation indicated that increased efficiency is required for this technique to compete with other thermal methods. Microwave efficiency could be increased by a flux configuration that minimizes soil penetration and maximizes absorption by plants, which, in turn, depends on plant growth form.

No abstract

A mathematical model was developed to get an equation of the decrease of air velocity crossing the canopy of tree crops during pesticide application using air carrier orchard sprayers. The utility of such a model rises from the need for an aid to understand the experimental results of several authors, who agree with the opinion that air jet velocity greatly affects environmental pollution from pesticides. Further, probably in the future it will arise the demand to implement the equation of air velocity decay in self-adjustment systems of the fan installed on orchard sprayers to limit spray drift. Based on momentum theorem applied under three assumptions, a differential equation was found and its integration lead to a closed 1282 Dario Friso et al. solution that can easily be implemented in a PLC for the self-adjustment system to develop. The integral equation thus obtained, together with the assumptions made, was submitted to on-field verification on three crops (peach, vine and apple). The results show a good correspondence between measured and estimated air speed as predicted by the mathematical model, with a relative mean error 3.3% and a maximum value of 6.2%.

No abstract

With the aim to gain a better understanding of the phenomenon of drift occurring during spray application of agrochemicals to agricultural crops, a laboratory testing was carried out using a wind tunnel under controlled environmental conditions (wind, temperature and relative humidity RH). Spray drift was measured with wind velocity of 1, 3 and 5 m/s and RH of 30, 50 and 70%. Under medium to high wind velocities the effect of RH was negligible. These results suggested to work out a simplified mathematical modelling by assuming the absence of droplets evaporation by means of closed solutions of the equations of the droplets motion. The main result of the mathematical model is the removal of the droplets smaller than about 80 μm from the spray produced by the nozzles.