Colorado

Prof. Gail Wicks, University of Nebraska weed scientist, is studying various crop rotations to help control jointed goatgrass (JGG) in winter wheat.

Initiated in 1996, results from this four-year study show rotations and wheat varietal selection do make a difference.

"Data suggests that farmers who plant taller wheat cultivars, use longer crop rotations and include spring tillage after wheat can reduce JGG seed production and soil seedbank populations," says Wicks.

Wicks' jointed goatgrass integrated management systems research is being conducted at the West Central Research and Extension Center, in North Platte, NE.

--Rotations aid in control: Wicks' study shows that JGG density, number of JGG spikes, joints and percentage dockage in harvested grain are greater in winter wheat-fallow (W-F) rotations than in wheat-ecofallow-corn-fallow (W-C-F), and winter wheat-ecofallow-corn-corn-fallow (W-C-C-F) rotations. Ecofallow practices include keeping wheat stubble weed-free with herbicides in the fall and spring. Herbicides also are used to control weeds in the corn and grain sorghum crops. In the spring, tillage was used in this study to plant JGG spikelets in half of the plots. The other plots were no-till. Tillage prior to planting corn and grain sorghum compared with no-till reduced JGG seedlings 50% in winter wheat. The W-C-F rotation had fewer JGG seedlings than the wheat-ecofallow-sorghum-fallow (W-S-F) rotation. The W-S-F rotation showed similar JGG densities to the winter wheat-fallow (W-S-F) rotation. The W-S-F rotation showed similar JGG densities to the winter wheat-fallow system.

"Grain sorghum continues to grow in the fall, drying out the soil and preventing JGG seed germination," explains Wicks. "Lower soil moisture following sorghum may reduce winter wheat yields (and plant competition) following the fallow phase of this rotation."

Corn plants die as they mature, leaving more soil moisture than sorghum to germinate JGG seeds in the fall. Wicks' data shows that JGG plant density and spikelet production was the lowest in W-C-F and W-C-C-F rotations.

--Tillage effects: The study showed that tillage in the spring after winter wheat is harvested the previous summer helps control JGG. The JGG biomass, number of spikes and number of joints were greater in the plots not receiving tillage in the spring. Dockage in harvested grain also was greater in the plots that received no tillage. "At some time, tillage is needed to encourage JGG seed germination," explains Wicks.

In a second study, Wicks is researching the effects of post-harvest tillage timing on JGG density in winter wheat in W-F rotation. The experimental area is kept weed-free with Roundup herbicide. Depending on moisture received during the growing season and after winter wheat harvest, tillage immediately after harvest can increase JGG seed germination. "It all depends on the weather and moisture conditions" explains Wicks. "If fields receive enough moisture, post-harvest tillage may stimulate more jointed goatgrass seed germination than waiting until the following spring to till."

"If growers have a light infestation of jointed goatgrass, they should consider light tillage immediately after wheat harvest before the soil becomes too hard," says Wicks. "If the infestation is fairly heavy, growers should use longer rotations incorporating spring crops with winter wheat and fallow. It appears that it would be wise to follow the first crop of corn with a second crop of corn. This would assure that sufficient time has been allowed to reduce viable jointed goatgrass seed density to an amount that would not affect winter wheat yield in a dry year."

--Wheat cultivar considerations: Winter wheat cultivars compared in this study include: Pronghorn, relatively tall variety; Alliance, medium-height variety; and Vista, short variety.

"Planting a medium-tall cultivar, like Pronghorn, reduces JGG seed production, compared to a short cultivar, like Vista," says Wicks. "Jointed goatgrass seed production may not be reduced by planting tall wheat cultivars every year. This probably is related to environmental conditions and fertility management. Getting the crop off to a fast start with planting time applications of starter fertilizer helps wheat compete with jointed goatgrass. Make sure that soil phosphorous and nitrogen levels are sufficient for good wheat growth."

Wheat producers can contact Wicks by phone at 308-532-3611 Ext. 151.

For more information on jointed goatgrass control, contact Eric Zakarison, National Jointed Goatgrass Research Program Extension coordinator, at 509-335-2451. Visit the jointed goatgrass Website, at http://jgg.unl.edu/.

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