Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/5/2006
Publication Date: 5/1/2006
Citation: Kegode, G., Forcella, F. 2006. Tillage effect on reproductive output by foxtail cohorts in corn and soybean. Weed Science. 54:419-427. Interpretive Summary: To make good long-term weed management decisions, some understanding of seed production of weeds that escape control is necessary. For this reason, we examined the number of seeds produced by isolated green and yellow foxtail plants as influenced by crop type (corn or soybean), tillage system (moldboard plow [MP], chisel plow [CP], ridge till [RT], spring disk [SD], and no till [NT]), and time of weed seedling emergence (before, with, and after crop emergence). Green foxtail typically produced twice as many seeds as yellow foxtail with maximum seed production being about 12,000 seeds per plant in green foxtail and 3,000 seeds per plant in yellow foxtail. In many cases, more seeds were produced in soybean than in corn. In corn, more seeds tended to be produced in NT than other tillage systems, whereas in soybean relatively few seeds were produced in NT compared to other tillage systems. Weeds that emerged before the crop or with the crop almost always produced more seeds than late-emerging weeds. Seed production was related closely to the number of flower heads; the number of flower heads was dependent upon the number of tillers (stems) that were present in mid July. Thus, levels of eventual seed production can be assessed in mid July, six weeks prior to actual seed production. These results will allow scientists, extension personnel, and agrichemical industry representatives to make better estimates of seed production for the improvement of long-term weed management strategies.
Technical Abstract: Reliable estimates of vegetative growth and fecundity of weeds require determination of production under field conditions in the presence of crops. Research was conducted in 1996 and 1997 to measure vegetative (primary tiller number per plant) and reproductive output (panicle number and size, and number of seeds produced per plant) at the end of the growing season by three cohorts of green foxtail and yellow foxtail growing in corn and soybean. Five tillage systems were studied: moldboard plow (MP), chisel plow (CP), ridge till (RT), spring disk (SD), and no till (NT). The first foxtail cohort (cohort 1) emerged prior to crop emergence, the second cohort (cohort 2) emerged at the same time as crop emergence, and the third cohort (cohort 3) emerged after crop emergence. Most primary tillers and panicles per plant were produced by green foxtail in MP and NT tillage systems and with cohort 1 plants. Yellow foxtail plants produced more primary tillers and panicles in 1996 in MP and SD tillage systems, in soybean, and with cohort 1 plants. Fitted linear functions predicted that each additional primary tiller per plant would yield 1.8 green foxtail panicles per plant (r2 = 0.77) and 1.6 yellow foxtail panicles per plant (r2 = 0.80). Panicle size was variable between years, among tillage systems and cohorts, and between crops and averaged between 3.6 to 5.9 cm for green foxtail and 3.7 to 5.8 cm for yellow foxtail. In corn, green foxtail seed number per plant was highest in NT with no consistent pattern among cohorts; whereas it was highly variable in soybean. Yellow foxtail seed number per plant was variable among tillage systems and cohorts with each crop. Foxtail seed number per plant was highly correlated to number of panicles per plant (r2 values = 0.68 to 0.94). These results incorporate the combined effects of competition from crops, level of soil disturbance (tillage system), and time of weed emergence and improve current estimates of green foxtail and yellow foxtail seed production, which may aid decision-making for long-term weed management.