The exemption for producers selling under $25,000 is for a new FDA regulation, the Produce Safety Rule. This exemption does not impact your responsibility to report and pay income taxes on the income.
If you sell less than $25,000 you are not subject to the FDA's Produce Safety Rule as described here: http://www.fda.gov/Food/GuidanceRegulation/FSMA/ucm334114.htm
You do still have to report this income to the IRS as part of your federal tax return even if you are exempt from the FDA rule. There is no IRS rule exempting you from reporting your income if your sales were less than $25,000.
