To control the density of herbicide-resistant water foxtail (Alopecurus aequalis), which has become more prevalent in the wheat fields of northern Kyushu, we employed a “twice shallow tillage seeding technique” as an integrated weed control system. From 2009 to 2012, we conducted field experiments in Oki, Mizuma District, Fukuoka Prefecture, to determine the effects of this technique and late seeding regarding the control of water foxtail and the enhancement of winter wheat growth. The “twice shallow tillage seeding technique” involves two rounds of shallow tillage to a depth of 0 to 5 cm, the first after the harvest of paddy rice without seeding and the second with seeding. This technique promoted the germination of water foxtail seeds buried from 0 to 5 cm and allowed for the control of emerged water foxtail using foliar applied herbicides before wheat seeding. The rates of water foxtail emergence before wheat seeding were over 170% those of the conventional seeding method at the end of November and mid-December. Compared with the levels prior to shallow tillage after the harvest of paddy rice, the number of water foxtail seeds buried from 0 to 5 cm decreased to approximately 40% by the end of November and to approximately 10% by mid-December. The number of water foxtail plants in March was reduced to 11% of that under the conventional seeding method using the “twice shallow tillage seeding technique” in conjunction with late seeding, while the number was reduced to 36% of the control using the experimental technique in conjunction with conventional seeding time. The yield of wheat under the experimental technique was equivalent to that under the conventional seeding method, and the yield under late seeding could be made equivalent to that under the conventional seeding by increasing the seeding rate. The density of herbicide-resistant water foxtail can be reduced with the combination of the “twice shallow tillage seeding technique” and late seeding while maintaining expected wheat yield levels.
Morningglories (Ipomoea spp.) are problematic weeds in soybean fields under upland-paddy rotation in Chubu region, Japan. This study monitored the emergence of morningglories and their growth in this setting. Morrningglories emerged following paddy rice rotation, originating from soybean cultivation in the year prior to rice rotation. A lot of them emerged when paddy rice was harvested in late August to early September but very few of them emerged when paddy rice was harvested in late September to early October. The following were noted: I. hederacea Jacq., I. hederacea var. integriuscula A Gray, I. lacunosa L., I. triloba L. and I. coccinea L. The emergence depth of I. coccinea was 0.5 cm in stubble field soil, much shallower than in soybean fields. I. hederacea, I. hederacea var. integriuscula, I. lacunosa and I. triloba emerged in mid-September in the two paddy rice stubbles where paddy rice was harvested in September 4, 2010. They had already started flowering at the plant height of around 15 cm and produced both immature and mature seeds except I. triloba. These data indicate that flooding associated with the single season paddy rice cultivation can not completely kill residual seeds of morningglories in the soil.