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Title: LIMITING GREEN AND YELLOW FOXTAIL SEED PRODUCTION FOLLOWING WHEAT HARVEST

Author
item KEGODE, GEORGE - UNIVERSITY OF MINNESOTA
item Forcella, Frank
item DURGAN, BEVERLY - UNIVERSITY OF MINNESOTA

Submitted to: Weed Technology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: After wheat is harvested in the northern Great Plains of the U.S. and Prairie Provinces of Canada, producers often observe a re-greening of their fields. The green color comes from growth of weeds, primarily green and yellow foxtail. Producers were unsure of whether this new growth arose from newly emerged seedlings or from older plants previously suppressed by the wheat canopy. Producers also asked whether these late-growing weeds had enough time before first frost in autumn to produce viable seeds that would plague their crops during the following growing season. More importantly, if viable seeds were formed, producers wanted to know the time window when seed production of these weeds would be most susceptible to control. The answers to these questions are as follows: (1) Re-greening of fields is from previously suppressed older plants, not newly emerged seedlings. (2) If wheat is harvested in mid-August or earlier, foxtails have sufficient time to produce up to 1000 viable seeds per square foot of soil surface. (3) Few seeds will be produced if either shallow tillage or a burndown herbicide (for example, glyphosate) is applied within two weeks following wheat harvest. (4) The above results are equally applicable to no-till, reduced till, and moldboard plowed fields. These questions arose directly from producers in the northern Great Plains, and the answers should allow them to make management decisions that will increase their long-term control efforts.

Technical Abstract: Green and yellow foxtail seed production following harvest of spring wheat is a major concern of producers in the northern Great Plains of the United States and the prairie provinces of Canada. Experiments were conducted in 1996 and 1997 in three tillage systems: no-till (NT), chisel plow (CP), and moldboard plow (MP), at the University of Minnesota West Central Experiment Station, Morris, MN, to determine whether time or glyphosate application, or tillage after wheat harvest could reduce post-harvest foxtail seed production. In both years, hard red spring wheat was planted in late-April fenoxaprop plus, 2, 4-D ester plus MCPA Ester was applied for grass and broadleaf weed control. Following wheat harvest each plot was subdivided into seven subplots. One subplot was disked twice at four to six days after wheat harvest. Each of five other subplots had glyphosate (0.25 kg ai/ha) applied on different days (1 to 31 DAH), and one subplot was the untreated control. Foxtail seed rain was collected from the soil surface following first frost and the number of green and yellow foxtail seeds determined. Tillage done immediately after wheat harvest eliminated foxtail plants and no new foxtail seedling emergence occurred despite ideal post-harvest conditions in 1997. Most viable green foxtail seeds were consistently obtained in NT plots, whereas yellow foxtail seed production varied among tillage systems. Tillage soon after wheat harvest, or glyphosate application within 16 DAH reduced green and yellow foxtail seed production by greater than 70%.