Infestations of Eoreuma loftini (Dyar) and Diatraea saccharalis (F.), the Mexican rice borer and the sugarcane borer, were quantified on non-crop grasses in an agroecosystem dominated by rice. Surveys conducted in the main Texas rice area during the spring of 2007 showed that until June (1 to 3 months after planting), rice did not host stem borers. However, stem borers built up in weedy rice field margins, where E. loftini larvae occurred at a density of 0.22 immatures/m2 on the first week of April. Prevalent grasses were the annual Phalaris spp., Lolium spp., and Bromus spp., but also the perennial Johnson grass (Sorghum halepense) and Vasey grass (Paspalum urvillei). Vasey grass harbored 63.6% of the recovered E. loftini. During the last week of May, E. loftini density averaged 1.47 immatures/m2. Johnson grass and Vasey grass, the prevalent hosts at that time, harbored 38.5% and 51.4% of E. loftini infestations, respectively. During the summer of 2006, in addition to Johnson grass and Vasey grass, Amazon sprangletop (Leptochloa panicoides), broadleaf signal grass (Urochloa platyphylla), and barnyard grass (Echinochloa crus-galli) were grown in a greenhouse and subsequently exposed to natural stem borer infestations. More than 25% of the plants for each grass species sustained boring injury after 30 days. Borer density attained 0.38 and 0.28 (Johnson grass), 0.05 and 0.03 (Vasey grass), and 0.80 and 0.60 (Amazon sprangletop) E. loftini and D. saccharalis immatures/plant, respectively. Potential IPM tactics impacting stem borer population dynamics with non-crop grass hosts will be discussed.