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Adhesion and Retention: primary adhesion occurs if droplets stick on first impact; secondary adhesion occurs from capture of droplets on secondary impact after bouncing or capture of daughter droplets caused by shatter of the initial droplet. Overall capture by these processes is plant retention, provided there is no spray run-off caused by excessive spray volume or incorrect formulation effects.
Adjuvants affect:
- Spray quality.
- Dynamic surface tension.
- Leaf wetting.
- Impaction processes.
Retention is also affected by plant architecture, leaf form and leaf surface character.
It can also be measured by using tracers as for deposition.
Retention can be modelled for single leaf or whole plant scenarios.
Impaction processes can result in droplet reflection or sticking, bouncing and recapture or shatter and the daughter droplets being captured. The main factors in impaction processes are droplet volume, velocity, solution dynamic surface tension, and leaf surface character.
Droplets bouncing off leaf. Droplets with adjuvant "sticking" to leaf.