tank mix: el agente tensoactivo se añade al momento de diluir el concentrado con agua en el depósito

built-in: el agente tensoactivo viene incorporado en la formulación del concentrado

en completo:

"que se mezcle con el agente tensoactivo en el depósito o que lleve incorporado en su formulación un adyuvante..."

(en el segundo caso el adyuvante es el agente tensoactivo)

"built-in": incorporado

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Note added at 56 mins (2012-05-11 11:15:48 GMT)
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en esta referencia que habla de "bioperformance enhancers" como en tu texto, no caracterizan el "adyuvante" de "agente tensoactivo", por eso cambio mi respuesta así:

"que se mezcle concentrado y adyuvante en el depósito o que el concentrado lleve incorporado en su formulación un adyuvante..."

An auxiliary, which is added to increase the effectiveness of an agrochemical, is called ***adjuvant***. This may be due to several modes of action, such as facilitated wetting, penetration, or better retention. Our Synergen® brand offers a range of proven ***bio performance enhancers***.

The term "adjuvant" is often used for additives which are added to the spray liquid in the tank before application (so called ***"tank-mix adjuvants"***) while adjuvants incorporated in the formulation are called ***"built-in” or “in-can adjuvants"***. Adjuvants are traditionally most frequently combined with herbicides, however the use for fungicides and insecticides is increasing.
http://www.cropprotection.clariant.com/C12576720021BF8F/vwWe...