One of the most common diseases of cacti is scale, which appears as flat, pinhead-size insects that appear as tan/brown spots. The scale functions as a kind of shield for the insects that feed on the plant sap and can transmit virus diseases between plants. You can find scale on columnar cacti such as Cereus Peruvanius and Euphorbia Ingens.

If you find these scale insects on your plants, you can try different treatments. The environmentally friendly method of controlling scale is to spray the plants with a mixture of rubbing alcohol and water. Because scale is an insect that sticks to the plant with a hard outer coating, it can be quite resistant to insecticides. If the scale infestation is not serious, then try to pick off or scrape with a sharp knife. Any physical removal of the scale might leave a mark or scar on the plant.

After physical treatments fail, you can use insecticides such as Orthene or acephate) can be injected into plants or used as a soil treatment to kill established scale insects. These materials generally are translocated within the plant in highest concentrations to the newer growth.