The hypothesis forms the foundation on which the experimental procedure is built. Knowledge of the ecology of the agents and the weed is necessary so that testable hypotheses are formulated, appropriate treatments are applied to the plants, and that efficacy is measured in such a way as to test the hypothesis. There is no point having a carefully thought out and rigorously executed experimental design if the hypothesis tested was of no value or, worse, not actually testable.

The measure of control agent efficacy must be appropriate for the plant in question. For example, in a woody weed with a seed bank any damage to the plant tissue is probably irrelevant at the level of the weed population unless it impacts on either plant longevity or on seed production or viability. In contrast, for water weeds that mainly reproduce vegetatively, damage to the growing tips of the plant may be critical. As stated previously, effects on population dynamics of the weed population must be assessed rather than simple measures of damage alone.

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