Predicting atmospheric concentration of pheromone in treated apple orchards

A Lagrangian model was developed to predict the vertical distribution of ph eromone in apple orchards treated with synthetic pheromone released from po lyethylene tubing dispensers. Measurements of tree dimensions' dispenser he ights, air temperature, and wind speed were used as inputs to the model. Da ta to test the model output were obtained by air sampling and capillary gas chromatography to determine atmospheric pheromone concentration. The model predicted highest concentrations of pheromone in the plane of the dispense rs. Predicted and measured concentrations were in the range 0.5-5 ng/m(3) f or blocks treated with 1000 or 2000 dispensers/ha. Mean wind speed had a la rge influence on pheromone concentrations within the canopy with concentrat ions decreasing at higher wind speeds. Wind speeds <0.1 m/sec, which repres ent good dying conditions for moths, resulted in high levels of mean pherom one concentration. Dispenser height had only a small influence on the maxim um pheromone concentration, with the peak concentrations decreasing with in creasing application height. The lower peak concentration for an elevated d ispenser occurred mainly because wind speeds were higher in the upper parts of the tree canopy. Air temperature, dispenser density, and pheromone rele ase rate (as inferred by dispenser liquid length), also had a significant i nfluence on pheromone concentration because of the linear relationship betw een these parameters and the corresponding flux of pheromone released into the treated orchards. We use known scaling relationships to demonstrate the se effects.