Spray retention on whole plants: modelling, simulations and experiments

• A new model is developed for simulating agrichemical spray retention by plants.
• The model predicts various outcomes from spray droplets impacting on leaves.
• Experimental data is obtained by spraying five mixtures onto cotton, wheat and fat hen.
• There is good agreement between the model predictions and the actual spray retention.
• Certain features of droplet impaction are identified as needing further investigation.

Retention of sprays on plants is a critical component influencing the effectiveness of agrichemical applications. Previous simulations of spray retention by plants gave poor agreement for hard-to-wet species when compared with actual measured retention. A new model is developed here that accounts for: species wettability, impaction angle, droplet bounce, partial retention on shatter, a variable time to shatter, and the number of daughter droplets produced. The aim of this study was to compare predictions from the new model with data obtained by spraying five mixtures via five nozzles onto easy-to-wet cotton (Gossypium hirsutum L.), and hard-to-wet wheat (Triticum aestivum L.) and fat hen (Chenopodium album L.). The new model correctly predicts retention to be highest on cotton and lowest on wheat. The trend in both measured data and the model predictions is for retention to decrease with increasing droplet size, on all three plant species. Formulation is correctly predicted to have little influence on retention by easy-to-wet cotton plants and to enhance retention by the harder-to-wet wheat and fat hen plants. The parameters that describe partial retention on shatter and variable time to shatter have a substantial influence on retention, as they affect primary or secondary droplet capture. A better understanding of the kinetic energy effects and the interactions between the formulation and the leaf surface are needed to refine their input values.

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