Cochineal scale looks like white sticky mounds on the surface of the cactus. Inside the white sticky material are cochineal bugs and if crushed, a purple die exudes. Cochineal mealybug scale usually appears on prickly pear cactus and chollas, but it can also attack other cacti. To kill the cochineal mealybug, use a hose end sprayer. Fill 1/2 with insecticidal soap (Home Depot stocks) and the other 1/2 with water. You can mix malathian in the water to be more effective. You can substitute liquid dish soap for the insecticidal soap, but dish soap is not as effective. Set power sprayer on 1 or 2 oz per gallon and hose off the scale. This should kill the scale within 7 days. If the scale still has purple die after 10 - 14 days, spray again. During the winter months ONLY the most effective method of cochineal eradication is to spray with Volck Oil spray (dormant season insect killer) which can be purchased from your hardware store.