Most no-till growers in Nebraska control winter annual weeds by applying glyphosate at or just before planting their summer crop. Our research suggests that removing winter annual weeds in the fall, especially henbit, would be beneficial because this species can serve as an alternate host to SCN and its presence could result in a buildup of SCN populations over time. Fall control eliminates that potential. Our research also resulted in a method for predicting the pattern of emergence of several winter annual weeds. It turns out that some winter annual species have a very wide window of emergence, which could make their control more difficult.
Soybean cyst nematodes are an important pest in soybeans. Winter annual weeds have increased in soybean as a result of minimum tillage. Some winter annual weed species may serve as hosts to soybean cyst nematode (SCN). Therefore, the increased population pressure of these winter annuals could increase soybean loss associated with soybean cyst nematode. Our focus was to evaluate the potential of the winter annual weed henbit as an alternative host to SCN, determine if fall herbicide application would reduce SCN, and predict winter annual weed emergence to aid in scheduling the fall herbicide application.
Henbit is an alternate host to SCN. Although soybean is a better host for SCN reproduction in terms of number of cysts formed per plant, the number cysts produced per gram of root and the number of eggs per cyst did not differ between soybean and henbit.
Herbicide application during early henbit development substantially reduces SCN cysts and eggs. Glyphosate and 2,4-D were applied to henbit at different times after the plants were inoculated with SCN. The herbicide applications reduced the root and shoot biomass, as well as the number of cysts per plant and eggs per cyst compared to the nontreated control.
A thermal time model best explains the emergence of 9 winter annual weeds and the perennial dandelion as seen in the figure below. Accumulation of thermal time started on August 1 of each year and fall, winter and spring vertical lines represent the thermal time accumulated by the beginning of each season. The red, light blue, black and green colors represent fall-, mostly fall-, fall and spring-, and mostly spring-emerging species.