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Winter Wheat or Spring Crops? Only Your Jointed Goatgrass Population Knows For Sure!

F.L. Young, A.G. Ogg Jr., and J. Burns
1996 Proc. West Soc. Weed Sci. 49: 73-74
Abstract. Information on jointed goatgrass population dynamics in dryland winter wheat is limited. In the past, research has focused on weed control and winter wheat yield reductions by various jointed goatgrass populations. Subsequently this information was used to determine goatgrass/wheat economic thresholds. However, these short-term thresholds are of little value because jointed goatgrass cannot be controlled selectively in winter wheat. A long-term, holistic approach, in lieu of an economic threshold must be implemented for jointed goatgrass in winter wheat. A 3-yr study was initiated in 1992 to collect data such as weed seedling establishment, weed seed production, drop yield reduction, crop quality and price dockage.

Initially, jointed goatgrass spikelets were planted at densities of 2, 4, 8, 16, 32, 64 and 128 spikelets/m2 in winter wheat planted after spring dry pea. Weed seed production, crop yield, and plant biomass were measured. In an adjacent area, shattering of jointed goatgrass spikelets before harvest was determined to be 40%. To evaluate jointed goatgrass population increases, 40% of the total spikelets before harvest was determined to be initial goatgrass population was placed on the soil surface of the respective quadrant and the experimental site was planted to winter wheat for a second year. Weed seed production, crop yield and plant biomass were again measured. The first cycle of the study (wheat after pea followed by wheat after wheat) was conducted during the 1992-93 and 1993-94 growing season. The cropping cycle was repeated during the 1993-94 and 1994-95 growing seasons. Precipitation during the 1993-94 season was approximately 50% less than the precipitation during the other 2 yrs. Jointed goatgrass was more competitive and reduced wheat yield severely during the dry year compared to the other 2 yrs. Jointed goatgrass plant population and spikelet production increased greatly over the 2 yr cycle but varied with environmental conditions. As an example, when wheat was planted in spring pea stubble, 18 plants/m2 produced 2,170 spikelets/m2. In the following wheat crop (wheat after wheat) 140 plants/m2 were established and produced 7,975 spikelets/m2.