Nimblewill (Muhlenbergia schreberi) is a warm-season perennial grass (weed) native to the United States and Canada with low palatability. This species is dominant in many horse pastures in which bluegrass (Poa pratensis) is the primary forage. Tall fescues infected with endophyte fungae gives tall fescue plants greater competitividade ability and enviromental stress tolerance than their noninfected counterparts. The purpose of this study was to compare the relative competitiveness of nimblewill with bluegrass and tall fescues (Lolium arundinaceum) with or without endophytic fungi (strain AR584) through experiments using a replacement series design. Replacement series experiments were conducted in pots to evaluate the growth of species in a pure stand and in a mix stand with variables rates. Species competitiveness was evaluated based on the relative yield and relative yield total (and competitiveness index) of the dry weight of shoots from species grown together. Nimblewill was found to be more competitive than bluegrass, and all tall fescues were more competitive than nimblewill. Our results demonstrated that the presence of endophytes in three different tall fescues did not alter the competitiveness of these fescues with nimblewill, but the tall fescue Kentucky 31 was more competitive between tall fescues. Based on our finding, we concluded that fescues are recommended, especially without the endophytic fungi to suppress nimblewill in implantation of pastures to horses.

The main goal of this research was to evaluate the growth of nimblewill (Muhlenbergia schreberi), an emerging threat to forage grass. Our initial experiment was arranged in a completely randomized design, with 17 treatments (i.e., weeks) and 4 repetitions. Seventeen growth evaluations (i.e., treatments) were carried out every 7 days, totaling a 119-day cycle, followed by an analysis of the variables such as stolon number, length, number of leaves, dry matter, biological productivity, growth rate, and relative growth rate. A second experiment was conducted over a 5-week period to compare the growth variable between nimblewill plants and pastures. For all variables, the results showed that the weed grass developed slowly within the first 5 weeks after germination, indicating that this would be the best time to implement a chemical or cultural control measure. It was also observed that cultures with a rapid growth in the first 5 weeks after emergence could easily suppress weed growth. At the end of the experiment, stabilization of all variables was observed. However, additional observations are required to obtain more accurate results.