Objective  Efficacy and optimum application of Bacillus amyloliquefaciens B1619 to control Fusarium wilt on continuous cropping watermelons were investigated.

  Methods  A field experiment with a random block design was conducted for 4 consecutive years to examine the effects of the microbial agent applied by different means and dosages on the growth and disease occurrence of the watermelon and the major microflora in the rhizosphere soil.

  Results  At a rate of (18+9) g B1619 to fill each hole dug into the ground around the plants was the selected method to deliver a 43.20% increase on watermelon yield for the study. The sugar contents in the center and peripheral by the rind of watermelon and marketability of the harvested melons increased significantly with the application. The application also changed the rhizosphere microflora community where the continuous cropping of watermelon was practiced. The bacteria count in the rhizosphere soil was 1.93 times of control at flowering stage and 1.27 times at maturing stage, while the number of pathogens, Fusarium oxysporum, reduced to 33.38% of control at flowering stage and 37.19% at maturing stage.

  Conclusion  The “hole-digging” method of applying B1619 at (18+9) g/hole rendered a high yield, supreme fruit quality, and the much reduced incidence of Fusarium wilt on the watermelons.