Pesticide Registration Improvement Extension Act of 2018 This bill revises requirements for pesticide registration applications and their corresponding maintenance fees and registration service fees. (Sec. 2) The bill extends the authority of the Environmental Protection Agency (EPA) to collect annual fees to maintain the registration of pesticides (maintenance fees) through FY2023. Additionally, the bill increases the maximum (1) amount that the EPA may collect in total maintenance fees from $27.8 million per fiscal year to $31 million for each of FY2019-FY2023; and (2) annual maintenance fees for pesticide registrants, including small business registrants. The bill extends until the end of FY2025 a prohibition on levying pesticide registration fees not otherwise authorized as maintenance or registration service fees. The bill extends the prohibition on levying fees for applications involving pesticide chemical residues (tolerance fees) until the end of FY2023. (Sec. 3) The bill expands the permissible uses of the fees collected and deposited in the Reregistration and Expedited Processing Fund, including by allowing the fees to be used for any review under the Endangered Species Act of 1973 required as part of the pesticide registration review. The bill also establishes set-asides of funds for (1) the development and implementation of performance data requirements for products claiming efficacy against certain invertebrate pests of significant public importance, such as bed bugs; and (2) monitoring good laboratory practices with respect to inspections and data audits conducted in support of pesticide product registrations. The set-aside of funds for review of inert ingredients is extended through FY2023. (Sec. 4) Applications for an experimental use permit must conform to the requirements governing pesticide registration applications. (Sec. 5) The bill extends through FY2025 the authority of the EPA to collect pesticide registration service fees, with a two-year phaseout period in FY2024 and FY2025. The EPA must increase by 5% the application fees for covered applications of pesticides that are received in FY2020 and FY2021. After that, the EPA must increase the application fee by an additional 5%. No waiver or fee reduction may be provided for a letter of certification of registration, which is commonly referred to as a Gold Seal letter. The set-asides of funds for worker protection, partnership grants, and pesticide safety education are extended until FY2023. Funds for worker protection must emphasize field workers. The EPA must also evaluate the application review process, including identifying opportunities for streamlining the review of a new active ingredient in a pesticide or a new use of a pesticide. The bill extends and revises reporting requirements, including by requiring the EPA to provide additional information about pesticide cases it reviewed and the number of registration review decisions it completed. (Sec. 6) The bill revises the fee requirements for pesticide registration applications and their registration service fees. This includes revision of existing fees, the addition of new fee categories, and the revision of time frames in which the EPA is required to complete review of a requested action. (Sec. 7) The bill directs the EPA to implement specified final rules without revision by the end of FY2021. Specifically, the EPA must implement the final rules titled (1) "Pesticides; Agricultural Worker Protection Standard Revisions" published on November 2, 2015, and (2) "Pesticides; Certification of Pesticide Applicators" published on January 4, 2017. The Government Accountability Office must report on the effectiveness of workplace requirements for providing pesticide safety information to employees.