1. White Scale is the most common pest but is very easily treated. They are neat, white rows of sucking insects, usually under the leaves.They spread rapidly so treat as soon as you see them. You could use an aerosol insecticide, Oleum or cooking oil, but I prefer to use 'Spray and cook'. Once they have suffocated, scrape them off with a soft cloth, a toothbrush or a hard jet of water. 2. Cancer or Gall is caused by mites and is difficult to control. Cut off the leaves, but don't put them in the compost heap! It spreads rapidly so it may be better to destroy the plant. 3. Fungus are round brown or yellow spots and one can use a Fungicide but as recovery is slow it is better to cut off the affected leaves. 4. Snout Beetle tunnels down into the crown of the Aloe and is unseen on tall Aloes. Water with a systemic insecticide or spray the crown with an insecticide. 5. Rust occurs as spots on the leaves and can be sprayed or remove the leaves.