Weed Scientist
University of Wyoming
Laramie, Wyoming
1995 Proc. Central Great Plains Conference
Know thy enemy. Knowledge about the biology and ecology of jointed goatgrass is necessary to determine when, where, and how it is susceptible to different types of control strategies. Mapping jointed goatgrass locations in a field can greatly aid management decisions, knowledge of current practices and jointed goatgrass history provide valuable information for designing improved weed management strategies and limiting its spread. Jointed goatgrass often moves into the field from roadsides and field margins.
Changing tillage practices can have a big impact on jointed goatgrass infestations in a field. The ability of jointed goatgrass to germinate on the soil surface makes it adapted to conservation or no-tillage winter wheat production. Several factors contribute to changes in jointed goatgrass populations under conservation tillage. Vertical distribution of jointed goatgrass joints in the soil profile (Table 1) as well as seed longevity. Deep mold board plowing has been suggested to suppress jointed goatgrass by burying seed so deeply that successful emergence is limited (Table 2). However, only some of the joints on the soil surface are buried deeply enough to reduce emergence, and subsequent secondary tillage is likely to bring buried seed back near the soil surface.
Fit the punishment to the crime. Jointed goatgrass is a winter annual weed which causes serious yield and quality losses to winter wheat in 14 western states. The biology of jointed goatgrass makes it well adapted to explode under conservation tillage dryland wheat production systems; thereby, threatening the sustainability of dryland wheat production in the Central Great Plains. The increasingly wide spread and costly problems associated with jointed goatgrass in winter wheat cropland, and the absence of reliable herbicides for selectively controlling this weed in winter wheat demand integrated approaches to solving the problem.
Table 1. Effect of tillage system on jointed goatgrass seed (joint) distribution in soil, Archer.
| Tillage | ||
| ——————————–%joints—————————- | ||
4-6 >6
|
23 40
|
11 <1
|
Table 2. Seed depth and jointed goatgrass emergence, Archer.
| Days after planting | |||
| ———————–%joints producing seedlings——————– | |||
2 3 4 5
|
23 0 0 0
|
61 21 13 0
|
65 28 15 0
|
Do not put all your eggs in one basket. Employing several strategies in a coordinated form provides insurance that jointed goatgrass management strategies will succeed. Jointed goatgrass management strategies fall into two broad categories. Preventative measures make the physical and biological environment less favorable for buildup of jointed goatgrass populations. Suppressive measures reduce jointed goatgrass populations. Both preventative and suppressive measures are important in an integrated weed management system.
Preventative measures do not involve large additional costs, specialized equipment or other resource inputs. This method of control does, however, require good management. Weed prevention methods include such things as planting clean, weed-free seed, using proper field sanitation, cleaning farm implements when moving from field to field, preventing weeds present in a field from producing seed, composting manure before spreading, destroying seed viability before feeding to livestock and avoiding movement of livestock from weed-infested to weed-free fields without allowing time for the seed in their intestinal tract to be discharged.
Suppressive measures are designed to reduce jointed goatgrass populations to non-economic levels. Suppressive measures include such techniques as crop rotation, competitive crops, fertilization, tillage, herbicides, and biological control. Crop rotations are a planned sequence of crops grown in succession on the same field over an extended period of time. Rotations are extremely useful for control of jointed goatgrass because they prevent continuous and uniform management practices from being employed over an extended period of time. Crop rotations lead to the diversification of individual cropping practices. The more dissimilar the crops and their management practices are in a rotation to winter wheat, the less opportunity jointed goatgrass has to become a problem. Crop rotation from winter wheat-fallow to spring sown crops such as grain sorghum, legumes, sunflower and millet for 2 to 3 years have shown considerable promise for reducing jointed goatgrass seed populations in soil (Table 3). Not only do these spring crops mix up life cycles but they also allow rotation to herbicides that have good to excellent activity on jointed goatgrass.
Table 3. Effect of crop rotation on jointed goatgrass seed (joint) populations in soil, Archer.
| Year | |||
| ——————————–joints/m2——————————– | |||
W-M-W W-M-S
|
291 218
|
127 149
|
131 84
|
1W = wheat, F = fallow, S = sunflower, and M = millet.
Getting a crop to grow vigorously is often the most effective and economical weed control practice available. The potential contribution of crop competition to weed control is often overlooked. Shading is the primary means by which crop plants suppress weeds. The crop must have optimum stand establishment and develop rapidly enough to get ahead and stay ahead of jointed goatgrass. Any plant related factor or management practice that hastens shading by the crop favors the crop and enhances its competitive ability. Emerging from the soil first, having a height advantage or growing at a faster rate than jointed goatgrass are factors that provide a competitive advantage to the planted crop.
Crops can be manipulated and managed to optimize shading ability. Several cultural practices such as optimum plant arrangement, smaller distances between rows, higher practices seeding rates and proper fertility management can maximize shading by hastening crop canopy closure. Selecting well adapted fast growing varieties further favors the crop. Remember the highest yielding varieties are not necessarily the most competitive.