There are several effective ways to kill and control Japanese beetles:

• Hand picking and drowning: Pick the beetles off plants and drop them into a bucket of soapy water. This method kills the beetles quickly and prevents them from releasing pheromones that attract more beetles. Doing this in the morning when they are sluggish is best. Shaking or smacking plants to knock beetles into soapy water is also effective.

• Soapy spray: Mix dish soap with water and spray plants to kill beetles on contact. However, this can also harm beneficial insects, so use cautiously.

• Chemical insecticides: Use insecticides containing pyrethrin or neem oil at the first sign of attack. Pyrethrin is fast-acting but toxic to bees and aquatic life, while neem oil acts as an antifeedant and works best when applied early.

• Biological controls: Apply beneficial nematodes such as Heterorhabditis bacteriophora to the soil to kill grubs before they become beetles. Milky spore (Bacillus popillae) can also be applied to the soil as a long-term control for grubs. These methods take time to reduce beetle numbers but are safe for other wildlife.

• Companion planting: Planting garlic, scallions, marigolds, and catnip can repel Japanese beetles.

• Avoiding traps for small yards: Japanese beetle traps can attract more beetles to small gardens, so they are recommended only for large yards and should be placed away from plants you want to protect.

In summary, handpicking into soapy water, early use of pyrethrin or neem, and applying biological controls to soil grubs are the best integrated methods to kill Japanese beetles and reduce their populations effectively.