Emergence Timing of Winter Annual Weed Species in Nebraska.

Winter annual weeds are species that typically emerge in the fall, overwinter as small seedlings, and complete their life cycle in the spring. The objective of this research was to understand the emergence timing of key winter annual weed species in Nebraska. In order to accomplish this objective, research plots were established at Lincoln, Mead, and at two sites (irrigated and dry land) near Clay Center, NE, in 2010 and 2011. In July of each year, 1,000 seeds of each species were planted in 15x20x5 cm mesh cages installed between soybean rows. Soil temperature and moisture were recorded at 2 cm depth in the soil. Emerged seedlings were counted and removed from the cages on a weekly basis until no additional emergence was observed in the fall and resumed in late winter, and continued until emergence ceased in late spring. Three different emergence patterns were observed in this study: mostly fall, mostly spring, and emergence during both fall and spring. The majority of the downy brome seedlings emerged during early-fall (>97 %), whereas henbit, field pansy, tansymustard, and Carolina foxtail emerged late-fall (>96, 97, 89, 97 %, respectively). Field pennycress and shepherd’s-purse had the majority of the seedlings emerging in the spring (>83 and 71 %, respectively). Virginia pepperweed, dandelion, and purslane speedwell were the species that emerged during both fall and spring, whereas the proportion between fall and spring emergence was not consistent across site-years. In general, the majority of the winter annual weed species tended to present a consistent emergence pattern across locations. Understanding when and for how long weed species may be expected to emerge will enable growers to make better management decisions. The next step on this research is to incorporate the weather data collected into our analysis to develop predictive models for weed emergence.