Q. I have cacti that attract the red insect that covers it with the white cotton like substance. Would it help if I cleaned them off and then sprayed the cactus with Volck oil?
A. This is a red cochineal scale insect causing this white, cotton -like substance. They live under this cottony mass, sucking plant juices from the cactus and protected by their cottony house. If you push on this cottony mass with your finger, the insect leaves a red dye on your fingertip.
I used to spray cactus with a sweep nozzle on the end of a hose to knock off the white cottony stuff. It works but during the warm summers they are back infesting the cactus with their white cottony stuff in about one week. The secret to long-term control is knocking off the cottony stuff and then immediately spraying the cactus with a pesticide.
Oils like Volck Supreme by Ortho or Neem oil works for a while after you knock off the cotton mass. But they will be back.
I have not verified this but I heard that Volck Supreme oil has been discontinued by Ortho, the manufacturer. But that rumor has been floating around since 2014. Monterey and Bonide make good oils as well. All of them are insecticidal oils and kill insects by “smothering” them.
If you apply oils during the summer, apply in the early morning when temperatures are cool. The label warns not to use it when temperatures are too high. Spraying oils during hot summer months can result in plant damage. Never spray plants with flowers that are open because of honeybees.This insect will return so repeat sprays will required as these cottony masses begin to build again. There are other insecticides available giving better control but they have their downside so I hesitate to mention them. Try the oils first. Also try soap and water sprays.