Citrus Investment in Treatment and Research for U.S. Sustainability Act or the CITRUS Act This bill amends several agricultural laws to authorize various Department of Agriculture (USDA) citrus programs. The bill reauthorizes through FY2023: (1) the Emergency Citrus Disease Research and Extension Program, (2) the Citrus Health Response Program, and (3) the Huanglongbing Multi-Agency Coordination Group. (Huanglongbing, also known as citrus greening, is a disease that damages citrus trees and reduces citrus production. It is primarily spread through insects known as Asian citrus psyllids.) The bill extends the termination date for USDA's Citrus Disease Subcommittee from September 30, 2018, until the subcommittee determines that Huanglongbing and the Asian citrus psyllid no longer pose a threat to U.S. citrus production. The bill modifies the Tree Assistance Program to allow citrus producers to: (1) receive additional assistance under the program, and (2) have higher adjusted gross incomes while receiving benefits under the program. (The program provides financial assistance to qualifying orchardists and nursery tree growers to replant or rehabilitate eligible trees, bushes, and vines damaged by natural disasters, including disease.)