There are several approaches to controlling Japanese beetles on roses: spraying with a pyrethin-based insecticide, applying neem oil or simply removing the beetles by hand. After removal, you can prevent the beetles return by using an insecticide that targets the beetles grub or incorporating a product called "Milky Spore" that can prevent Japanese beetles for several years.
The first step in controlling Japanese beetles on roses is to kill the existing adult beetles. As mentioned above, there are several ways to kill adult beetles. Using a pyrethin-based insecticide kills the adult beetles through contact. This method is also an effective way to get rid of a variety of other beetles.
Applying neem oil kills adult beetles by reducing their feeding. Neem oil is a natural product that originates in trees.For this method to be most effective, apply neem oil as soon as you notice the beetles. Another natural method is hand removal. Because beetles are less alert in the morning, remove them in the morning, and drop them in a container of soapy water to drown.
The second step in controlling beetles is to kill or remove any grubs they have left behind. Beetles typically emerge in the spring, so apply a grub-killing product before that time for best results. Another option for grub removal and prevention is Milky Spore. After beetle grubs eat the Milky Spore, it kills them and causes the Milky Spore to spread through the garden. Milky Spore can take several years to fully spread; however, it can repel beetles for up to 10 years