Safer Insect Killing Soap is a good solution for tough insect pest infestations. It works as a contact insecticide and has no residual effect. Gardeners just spray this ready-to-use mixture onto their plants every 7-10 days and apply at least three times to break the pests' reproductive cycle. EPA No. for RTU is 42697-59 EPA No. for Concentrate is 42697-60.