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Rainfastness studies

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The residual activity and efficacy of pesticides can be significantly affected by rainfall occurring after an application





Therefore, rainfastness; a pesticides ability to withstand rainfall, is an important factor affecting the efficacy of foliar-applied pesticides.

The degree of rainfastness of pesticides is highly variable though a pesticide is considered rainfast after application if it has adequately dried or has been absorbed by plant tissues so that it will still be effective after rainfall or irrigation.

Our rainfall simulator can help you discern the level of rainfastness of your PPP


In the course of a rainfastness study, specimen plants are treated with the test substance using a purpose built track sprayer. They are subsequently exposed to the simulated rainfall.  This can typically be;

  • 0.5 hours post application
  • 1 hour post application
  • 2 hours post application
  • 3 hours post application
  • 6 hours post application

In addition, 2 rainfall regimes are commonly evaluated:

  • Medium rainfall 3mm/hour for 1 hour
  • Heavy rainfall 10mm/hour for 1 hour

Once the plants have been removed from the rain simulator and have dried, a range of methods may be used to evaluate the rainfastness of the test substance.

Specimens of the plants may be sampled and subsequently analysed in order to determine the precise amounts of test substance present.  This analytical phase would normally be performed by our in house analytical team.

Alternatively biological activity (efficacy evaluations) may be assessed (normally in the glasshouse or growth rooms).

In the case of a plant growth regulator, measurements of specific plant parts known to be affected by the test substance can be made over a period of time.

In the case of a herbicide, the percentage control of weed species known to be sensitive to the test substance can be made over a period of time.