Experimental use permits required under Section 5 of FIFRA can be used when conducting experimental field tests on new pesticides or new uses of pesticides on:

The correct answer indicates that experimental use permits under Section 5 of FIFRA are specifically required when conducting experimental field tests on new pesticides or new uses of pesticides involving 10 or more acres of land, or 1 or more acres of water. This regulatory requirement is in place to ensure a higher level of scrutiny and monitoring for more extensive tests that could potentially have significant environmental or public health impacts. Larger test areas are likely to pose greater risks and, therefore, necessitate oversight to assess the implications of pesticide use in those areas comprehensively.

Smaller areas, as suggested in other options, do not typically require the same level of regulatory scrutiny because the risks associated with testing new pesticides on those scales are deemed less significant. For example, testing on less than 10 acres would not trigger the same type of permits, streamlining the process for smaller scale studies while still ensuring that larger tests are monitored for safety.