It appears that rotenone (a powerful piscicide) is actually banned [0]. Same document also indicated that copper sulfate use is limited to specific situations/crops. Though, of course, conventional crops also have restriction on the use of pesticides, presumably they are less restricted.

[0] https://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&SID=9874504b6f1...

edit: This, of course, only applies to the USDA organic program. Products produced elsewhere may have different rules.