Q.violets yellow and papery
The leaves on my outdoor Violets have turned all yellow and papery. I don’t see any sign of spider mites (there are sticky webs but spider mites aren’t there?). I am not sure what is happening to them – they have been really healthy in the past. The violets are in a north facing garden and up until two years ago were very healthy.
There could be many reasons actually. One of them is that violets need sun only partially and if they are exposed to it too much or the sun is just too strong in the last two years, they can start withering and dying from the heat. Another reason is over-watering or not enough water as well. When you over-water your plants, the leafs turn yellow, but inside the ground the plant is rotting. And when there's not enough water it just dries. In this case you could try installing an irrigation system - http://www.fantasticgardenersmelbourne.com.au/irrigation/ , which will not only make sure your plants are watered on time, but also with the exact amount of water they need.
Another reason for your trouble could be the quality of the soil. Violets need a lot of nutrients in order to grow, and if you're not fertilising the ground regularly, then maybe the soil is just too exhausted to keep it going. You should definitely check all these options. Of course, diseases are also quite common, so you should never rule them out completely.