|Ogg Jr, Alex - Retired Ars Employee|
|Alldredge, J. - Washington State University|
Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2014
Publication Date: 5/20/2014
Citation: Young, F.L., Ogg Jr, A.G., Alldredge, J.R. 2014. Postharvest tillage reduces Downy Brome infestations in winter wheat. Weed Technology. 28:418-425. Interpretive Summary: Downy brome continues to be a major pest in the Pacific Northwest winter wheat producing regions especially in the low-rainfall area where the winter wheat-summer fallow rotation is the common production practice. In this region, growers will generally leave wheat stubble standing over-winter and perform a primary tillage operation in the spring. This practice however may allow downy brome to become dormant in which case the seed persist and the weed remains a problem in the subsequent crop. We evaluated the effect of postharvest tillage on the vertical movement of downy brome seed in the soil, seedbank depletion in fallow and plant densities in the subsequent winter wheat crop. Disking and using sweeps distributed more downy brome seed throughout the soil profile to depths of 12 cm than either harrowing or no-tilling. In fact, 75% of the postharvest seed was found either on the soil surface or 0 to 3 cm deep in no-till compared to 75% of the seed found from 0 to 6 cm deep with disking. In spring samples, there were significantly less downy brome seed that germinated at the 0 to 3 cm depth with disking and using sweeps compared to harrowing and no-tilling which indicates soil seedbank depletion with these implements. The use of sweeps and a disk significantly decreased downy brome populations one year later in the subsequent wheat crops. The use of these tillage operations can be integrated into weed management strategies by farmers to reduce downy brome competition and herbicides in the growing crop.
Technical Abstract: In the Pacific Northwest, downy brome continues to infest winter wheat producing regions especially in low-rainfall areas where the winter wheat-summer fallow rotation is the dominate production system. In Washington, a study was conducted for 2 years at each of two locations in the winter wheat -summer fallow region to determine the influence of four postharvest tillage treatments on vertical seed movement, seedbank depletion, and plant densities of downy brome. The four tillage implements included a disk, sweep, harrow, and skewtreader. The study also included a no-till treatment for comparison. The sweep and disk had the most vertical movement of downy brome seed compared to the no-till treatment. Approximately 75% of the fall postharvest seed in the no-till treatment was located either on the soil surface or in the 0 to 3 cm depth at both locations. In contrast, 75% of the seed in the disked treatment was located from 0 to 6 cm deep at both locations. The disk and sweep both decreased downy brome seed in the soil at the 0 to 3 cm depth compared to the harrow and no-till treatments. There was no difference in the downy brome plant densities following postharvest tillage in the summer fallow due to any of the treatments. However, plant densities in the subsequent winter wheat crop were reduced by the disk, sweep, and harrow compared to the no-till and skewtreader treatments. In general, seed densities as affected by the skewtreader fell between the disk and the no-till treatments. The use of sweeps and the disk should be integrated into a weed management strategy for downy brome in the wheat-fallow region of the Pacific Northwest.