Vulpia myuros (L.) C. C. Gmel

Akhter, Muhammad Javaid, Kudsk, Per, Mathiassen, Solvejg Kopp & Melander, Bo, 2021, Rattail fescue (VulpiO myuros) interference and seed production as affected by sowing time and crop density in winter wheat, Weed Science (Cambridge, England) 69 (1), pp. 52-61 : 55

Vulpia myuros Cumulative Emergence

Crop density had no effect on the cumulative emergence of V. myuros , and the data were therefore pooled across crop densities, and parameter estimates were compared between sowing times ( Table 2 ; Figure 1 ). In the 2017 to 2018 growing season, V. myuros seeds sown at normal and late sowing times initiated emergence ( GERM 10) at the same time (124 and 123 thermal time [ C], respectively); however, time to complete the emergence ( GERM 90) was more rapid at late sowing time (196 C) than normal sowing time (303 C). Similar to the previous growing season, in 2018 to 2019, V. myuros initiated emergence ( GERM 10) at the same time at the two sowing times (138 and 132 C, respectively), however, the influence of sowing time on duration of V. myuros emergence was reversed. For instance, time to complete the emergence ( GERM 90) was greater for late sowing time (393 C) than for normal sowing time (303 C). The rate of emergence indicated that in the 2017 to 2018 growing season, V. myuros seed sown at late sowing time showed very rapid emergence rate (f = −9.5) compared with normal sowing time (f = −4.9). In contrast, differences in emergence rates were minor in the 2018 to 2019 growing season, with f = −5.6 at normal sowing time and f = −4.0 at late sowing time.

As late sowing time in the growing season of 2017 to 2018 corresponded to very late sowing under normal conditions (November 10), V. myuros seeds encountered more cold days and probably required more days for the accumulation of the heat units required to initiate emergence ( GERM 10). After the initial germination, seeds of V. myuros completed emergence ( GERM 90) more rapidly than at normal sowing time. The potential of V. myuros to emerge at low temperature has also been reported in previous studies, where V. myuros emerged at 1 C ( Scherner et al. 2017b) or 0 C ( Ball et al. 2008). Although V. myuros seeds sown at late sowing time exhibited a rapid emergence rate and finished emergence earlier in the 2017 to 2018 growing season, the total number of seedlings was lower compared with normal sowing time. However, in the more normal 2018 to 2019 season, sowing time had no effect on the total number of seedlings of V. myuros .

The rate and duration of emergence are key factors influencing weed competitiveness, susceptibility to different control practices, and generative potential ( Forcella et al. 2000). The current study showed that V. myuros emerged rapidly with lower GERM 90 values at normal sowing and late sowing times (303 and 393 C, respectively) under normal field conditions than, for example, annual bluegrass ( Poa annua L.) (754 C), another common grass weed in Denmark ( Scherner et al. 2017b). Rapid emergence gives V. myuros a competitive advantage over winter cereals early in the growing season ( Dillon and Forcella 1984). The rapid germination at late sowing time in the 2017 to 2018 growing season reflects that V. myuros can germinate under low temperature and light conditions. These findings are similar to observations by Dillon and Forcella (1984), who reported that V. myuros emerged rapidly and under a wide range of light and temperature conditions. Similarly, a recent study showed V. myuros germination under wide range of temperature, light, and pH conditions ( Weller et al. 2019). The effect of sowing time on the emergence of V. myuros reported in our study was inconsistent across years, probably because of very different growing conditions in the two growing seasons. In practice, the main objective of delayed sowing is to reduce weed competitiveness by reducing weed densities, delaying weed growth relative to crop growth, and reducing the survival of grass weeds during the winter ( Melander et al. 2005). However, this effect cannot be expected in the present experiment, in which dry weed seeds were seeded at the time of crop seeding ( Melander 1995). Non-dormant weed seeds naturally present in the soil are already imbibed and ready to germinate immediately after seedbed preparation, and this could influence emergence pattern, especially the time of initiation of emergence. In practical farming, preparing a seedbed but delaying sowing time (stale or false seedbed) means that many V. myuros seeds, due to their rapid germination rate, will emerge before and can be controlled mechanically or chemically before crops are sown. A study conducted in Denmark indicated that a stale seedbed could reduce density of V. myuros up to 80% ( Jensen 2019).

Figures

Figure 1. Cumulative emergence dynamics of VulpiO myuros at normal sowing time and late sowing time in relation to thermal time (C) in 2017–2018 (A) and 2018–2019 (B). Regression equation and parameter estimates described in Table 2.