Journal of Weed Science and Technology

In Nagano Prefecture farms where wheat is repeatedly cultivated, the frequent occurrence of naturalized Brassicaceous weeds, Camelina microcarpa Andrz.ex DC., Descurainia sophia (L.) Webb ex Prantl and Thlaspi arvense L., caused some farmers to abandon growing wheat. To establish a cultural weed control method during the summer immediately after the wheat crop, we examined the influence that farm management practices have on seed survival of the three weed species.
Under normal field conditions, most seeds of the three weed species were completely viable. In two-month trials of farms undergoing a rotation from flooded to dry field conditions, the percentage of germinated weed seeds varied from 0 to 90% depending on the annual soil moisture conditions.
In paddy fields, germination of the three weed species decreased to around 10% and less than 1% with 1 and 2 months flooding, respectively.
In the fields converted from paddy fields that Thlaspi arvense L. tended to dominate, the soil seedbank decreased to about 5,400 seeds/m^-2 after conversion to paddy field cropping from 90,000/m^-2 before planting. However, after converting paddy fields back to wheat farming, the weed plant density returned to 75/m^-2, corresponding to a high infestation level.
In summary, summer flooding effectively suppressed the three weed species; however, to effectively suppress weed outbreaks in heavily infested fields at least two successive conversions of upland fields into paddy fields are necessary.

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This study studied effects of day length on heading of centipedegrass (Eremochloa ophiuroides (Munro) Hack.) to evaluate influences of this species on ecosystems. Plant materials of two strains by vegetative propagation in the previous year of the experiment (both strains derived from ‘TifBlair') and four strains by seeding in the year of experiment (‘TifBlair' and three selling companies' common) were treated by three day lengths for 156 days. Day lengths were 13 hr (13 h), 16 hr (16 h), and 16 hr for 62 days and 13 hr for the following 94 days (16→13 h). Temperatures were regulated at 30°C 8 hr/25°C 16 hr in all treatments. In vegetative strains, the percentage of plants in the reproductive stage (PRS) were high in 13 h and 16→13 h, and days from the start of treatment to first heading in 13 h were shorter than these in 16→13 h. In seeded strains, PRS were highest in 16→13 h. PRS of all strains were lowest in 16 h. In all headed plants, dry weights of the aboveground part at first heading were 22.2 g or more, which indicates that centipedegrass has a basic vegetative phase preceding the photoperiod sensitive phase. Plants immediately after the beginning of the photoperiod sensitive phase would be ‘long-short day plants', but would become ‘short-day plants' with progression of age. In Japan, centipedegrass is suitable for growth in prevailing climates from southern areas up to the southern Tohoku district. Results of this study indicate that centipedegrass can head under day length conditions in these regions. These characteristics should be considered during evaluation of the influences of centipedegrass on ecosystems.

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