Jointed Goatgrass

Identification

Photo: Jointed GoatgrassAnnual; Foliage is a deep bluegreen. Prior to seed formation plants tend to lie flat on the ground. Spikelets are awned, the longest awns at the top of the spike. Seedheads break into individual segments at maturity.

Economics

Ten jointed goatgrass plants square feet can reduce cereal crop yields by 30 to 50%. Jointed goatgrass seeds are a contaminate in cereal grain seed crops.

Chemical Control

There is no selective control available for in-crop sites. Non-crop controls are available.

Cultural Control

Seed bed preparation in the fall with an application of a contact herbicide, followed by a spring planting. Followed by a year of fallow, and then back to a winter crop. Establishment of perennial crops or grasses in an option in non-crop areas.

Estimating Jointed Goatgrass losses

For some of us weed fighting is a recreational activity from which we draw great personal satisfaction, yet weed control decisions in production agriculture must come down to an economic decision based on a positive cost-to-benefit ratio. Such analysis confronts us currently with jointed goatgrass, the Number #4 weed on Umatilla County's Dirty Dozen.

While Beyond© herbicide offers effective control of jointed goatgrass, it will have addition costs. The adoption of the Clearfield production system and Beyond© will only be feasible if additional costs in seed and herbicides are offset by increased yield.

To determine the potential for increased yield, I looked up some research from the 1980's conducted by now retired OSU Weed Scientist Don Rydrych. Rydrych's research at the Pendleton Experiment Station shows the competitiveness of jointed goatgrass in Stephens wheat (Table 1.). Yields were reduced in the range of 25% to 32% with goatgrass densities of 5 to 8 goatgrass plants/sq ft. At a 5 plants/sp ft. population there would be about 218,000 jointed goatgrass plants per acre.

Table 1. Goatgrass competition in Stephens winter wheat from 1981-83 at OSU, CBARC, Pendleton, Oregon *1
Treatment Year Goatgrass plants ft2 Avg. winter wheat yield Bu/A Yield Reduction Bu/A Yield Loss %
Weedy Weed free
1981 5 83 110 -27 25%
1982 8 53 74 -21 28%
1983 8 74 109 -35 32%
*1 Rydrych, D.J. 1998. Jointed Goatgrass published by the Oregon Wheat Commission and Oregon Wheat Growers League in cooperation with OSU-CBARC, Pendleton, Oregon. Work was conducted under OSU Project 242 and was supported in part by the Oregon Wheat Commission.

The results of a second study on the competitiveness of jointed goatgrass are shown in Table 2. The study was completed in Montana in 1995-1996 by D.B. Maxwell. It looked at jointed goatgrass plant densities ranging from 0.09/sq ft to 9/sq ft. Maxwell observed that jointed goatgrass densities of 1 per sq ft reduced winter wheat yields 10 to 13% depending on the year when using a 60 lb seeding rate.

These studies show how highly competitive jointed goatgrass is with winter wheat and give a perspective on how much yield can be loss even at fairly low population levels. The losses will vary from year to year depending how competitive the wheat is and when the goatgrass germinates. These results can be used to provide one with a general guideline on how much yield is potentially being lost to a relative level of jointed goatgrass. The math from there should be fairly straight forward to determine if the additional costs of the Clearfield system are justified in a particular field. This new technology is available as a tool to use when and where it fits on an economic basis and not for recreational weed control.

Table 2. Winter wheat yield loss in response to jointed goatgrass densities and winter wheat seeding rate at Broadview, Montana. *1
Jointed goatgrass
plants/sq ft
Yield loss
1995 1996
.09 1.3 1.6
.46 5.6 7.2
1 9.9 13.1
9 31.7 48.5
9 28.2 42.4
*1 Maxwell, B.D. 1998. Jointed goatgrass population dynamics in crop rotations. Natl'. Jointed Goatgrass Research Program. 1998

Progress Reports, Final Reports. Compiled by Alex Ogg, Jr. Copies available: Ag Research Center, WSU, Pullman, WA. 62.

 

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