Don W. Morishita and Robert W. Downard
1996 Res. Prog. Rep. West Soc. Weed Sci.A field experiment was conducted near Twin Falls, Idaho to determine the competitiveness of jointed goatgrass in dryland winter wheat (var. Stephens). The crop and jointed goatgrass were planted October 13, 1994. Winter wheat seeding rate was 60 lb/A in a 12-inch row spacing. Jointed goatgrass was seeded to obtain uniform densities of 5, 10, 25, and 50 plants/yd
2. Plots were thinned to desired jointed goatgrass densities in the early spring. The experimental design was randomized complete block with four replications. A postemergence application of bromoxynil and MCPA was applied at 1.0 lb/A for broadleaf weed control May 3. Jointed goatgrass and wheat were harvested by hand August 1. Jointed goatgrass seed number and yield and wheat yield were determined from each plot and averaged.
As jointed goatgrass populations increased, seed number and yield increased (Table). However jointed goatgrass seed yields decreased from 196 seeds/plant at a density of 5 plants/yd2 to 106 seeds/plant at 50 plants/yd2. Wheat yields decreased as jointed goatgrass plant density increased. There was no wheat yield reduction at jointed goatgrass populations of 5 and 10 plants/yd2 compared to the weed-free check. (Department of Plant, Soil, and Entomological Sciences, University of Idaho, Twin Falls, ID (83303)
Table1. Jointed goatgrass and wheat seed yield, near Twin Falls, Idaho.
| Jointed goatgrass |
Jointed goatgrass |
Wheat |
| density |
seed/acre |
seed weight |
yield |
| plants/yd20
5
10
24
47
LSD (0.05)
|
seed x 1060
4.7
7.1
13.9
25.7
4.8
|
lb/A0
415
602
1111
2059
405
|
Bu/A57
48
50
40
36
11
|