Southern Ag Pyrethrin Concentrate is labeled to kill beetles including Japanese Beetles. The label just does not break down every species it controls.
Southern Ag Pyrethrin Concentrate is not specifically labeled for Japanese beetles but likely would kill them if sprayed directly with the product during treatment. For residual control instead, you may use a product such as Talstar P. Please be sure to review the product label for more information and complete application instructions.
A part can be any measurement. For instance if you use one cup concentrate you would then need to use 19 cups of water. If treating for mosquitoes at the 1:19 ratio, you would use 8 oz of Southern Ag Pyrethrin Concentrate with 152 oz of water or 1.25 gallons of water.
