Abstract
To investigate the effect of late seeding on occurrence of soybean dwarf disease (SbD) in soybean (Glycine max (L.) Merr. Cv. Yukihomare), we conducted two field experiments at the National Agriculture Research Center for Hokkaido Region. 1) Examination of SbD occurrence rate and yield of soybean seeded at three date: mid-May (early), late May (standard), and early June (late). 2) Examination of SbD infection rate in the soybean seedlings grown in the field in different seasons. The yield of late-seeded soybean plants was equal to that of the standard-seeded plants, except in 2004 when typhoon damage reduced yield. The rate of SbD occurrence was highest in the early-seeded plants, and lowest in the late-seeded plants. The soybean seedlings exposed to the field from May 26 to June 15 had a higher rate of SbD than the others in both years. Late-seeded soybean plants emerged after the peak of the occurrence of the foxglove aphid (Aulacorthum solani (Kaltenbach)) which transmits soybean dwarf disease virus to soybean field, and this may be why SbD occurrence rate was low in the late seeded plants. When the occurrence rate of SbD was reduced by late seeding, the resulting yield reduction may be mitigated by dense planting. Thus late-seeding combined with dense planting may be effective in reducing SbD-caused yield reduction.
