Incomplete degradation of control products and subsequent carryover of active ingredient to the next year are operational concerns for control agencies. Altosid XR briquets were weighed before and after 6-18 months of exposure in temporary wetlands to determine the rate of physical degradation of the briquets. Degradation rate was influenced mainly by the number of days a briquet remained under water. The average briquet degraded to 19% of its weight within 150 days of immersion and was completely degraded after 1.5 yr under water. The active ingredient (methoprene) content of briquets declined faster among those exposed to air and more slowly among those that were immersed.