I know this post is old, but I have a nine year old silky hen who has been having the same thing in her nostril for about a month. It is just on the left side. It is crusty and hard on the outside but chunky like cottage cheese on the inside. It is yellow and smells absolutely horrible! It also seems to be eating away at her nostril. I pick out what I can every morning and apply Neosporin. When I get a really big chunk it seems to tear the nostril and there is some bleeding. Regardless of how much i remove, there is more the next day. She does have labored breathing, but seems normal other than that. She does share a coop with seven other chickens, and other than molting at a terrible time of year they are all fine. If anyone has any idea what this could be, please let me know.
Sometimes they can get feed stuck in the nose causing a blockage over time that turns into a concrete-like substance. It sounds like it could be canker. Could you post a picture? Have you looked inside at the roof of her beak? If it is canker, there may be yellow cheesy plaques inside the beak. Fish Zole (Flagyl, Metronadizole) is the treatment. For a silkie the dosage would probably be a lot less than the 250mg daily for 5 days that standard size chickens get. Here is some info and a link for fish zole: http://www.revivalanimal.com/Fish-and-Bird-Antibiotics.html
Oral Canker
Oral Canker is a condition which can be found in a wide variety of birds and most commonly in pigeons.
Causes
It is caused by a motile protozoal parasite called Trichomonas gallinae.
This parasite can cause caseous lesions of the mouth, pharynx, oesophagus and in certain circumstances, further down the digestive tract. These lesions can become extremely extensive.
This causes the birds to stop eating and drinking, in severe cases the extensive nature of the lesions combined with not eating and drinking leads the chickens to die.
Diagnosis
Diagnosis is often based upon clinical signs but wet smears can be examined under the microscope to confirm clinical suspicions. Speak to your vet.
Treatment
The treatment traditionally involved the use of a drug called Dimetridazole, however, this drug is no longer available or licensed for use in the UK.
The affected chicken in these photos was treated with Metronidazole, this is a UK licensed medication but is not used in poultry therefore it had to be prescribed under the rules of the Veterinary Medicines Directorate cascade. This also means that any eggs the chicken may lay during treatment and for a specified period after treatment would need to be discarded. Her eggs must never be sold for human consumption. The owner of the hen was extremely pleased with the outcome and has supplied us with plenty of photos to monitor the hen’s progress.