Without knowing more, it seems a logical deduction. If the "organic" pesticides were more effective than the "chemical" pesticides, farmers would always choose to use them. If the alternatives aren't as effective, then you need to spray more for the same result.
So this then claim stems not from knowledge but from a "seemingly logical deduction". It is clear that there is no actual substance to this idea that "organic farms often use more pesticides" - even the notion is false that "more pesticides" is a meaningful concept as it alludes only to pesticide weight or mass and ignores all qualities of the substances involved - in the accompanying "logical deduction" - such as ecological and biological impact.
Organic standards are not so simply drawn as to focus on the weight or mass or price of pesticides - they concern the ecological impact and risk of agricultural materials and practices.