This is seen as a crusty like, or raised scales on the legs; a bit like armour plating.
It is caused by a small parasite that burrows under the scales. If left untreated for a long time it can cause sever problems to the bird by causing the toe nails to become deformed and can cause a bird club leg ring, to become too tight.
Scaly leg is NOT a sign of old age as many people seem to think, Old birds can have nice legs too if kept free of parasites.
Scaly leg can be persistent and take a long time to correct, also the birds legs will never look as nice as if they had never had the problem; prevention is far better than cure.
There are a number of home made remedies which have reasonable success. The one I favour is to rub a small amount of cooking oil, such as Canola or Olive oil into the legs. This loosens the scales and suffocates the mite by blocking the burrows.
This treatmnent should be repeated weekly until the legs are free from scale.
Another remedy is to use a diluted disinfectant rubbed gently onto the legs, this supposedly has the same affect as the oil, but you need to be careful that you dont use too high a concentration, as it may burn the skin, particularly if the skin is broken.
A University of Surrey report quotes when using on Poultry
"For the more organic amongst you I have had very good results using Eucalyptus oil. This works like a penetrating oil and after a few minutes of use you will find some scabs becoming very soft and fairly easy to remove. Treat every few weeks. massage well into the legs. I have yet to try Tea tree oil but think that this mixed with Eucalyptus oil would prove useful due to its healing properties. "
NOTE: Eucalyptus Oil comes from an Australian native tree, usually the variety Eucalyptus polybractea or Eucalyptus globulus. The majority of the world production however is in China & Spain ref http://sres.anu.edu.au/associated/fpt/nwfp/eucoil/eucoil.html
Scaly Face & Leg Treatment - manufactured by aristopet 25ml or 100ml
University of Surrey
ANU - Australian national University
Author: James Hart - Published 05/05/05