My plum tree starts producing plums they start off green then turn yellow and drop off

Depends how much yiu have pruned. But it will be OK maybe a little less friut next year. :)

12 meters

If is in the shoes, consider using hand sanitizer to clean them out. Wear socks and it should be bettercnow. .

http://www.gardenguides.com/83554-diseases-plum-trees-cures.html

either too much water or not enough

I can only direct you the results of my search for 'PLUM TREE LEAVES SILVER' on the internet (AltaVista/Yahoo). Some pointed to for example
1. http://www.telegraph.co.uk/gardening/6205476/How-to-identify-silver-leaf-disease.html
2. http://www.which.co.uk/documents/pdf/silver-leaf-disease-153706.pdf
3. http://www.growsonyou.com/question/show/1213-plum-tree-silver-leaf-disease
These only the first three results of my search, I hope they are of some use. This seems to be a well known condition. Other similar searches using different search engines will throw up different results in a different order. I suggest you take a look at someof them, because personally I don't know the answer to your question

8.June.2014

I take help from online websites that have this service like helping in repair some like reliable-store
have instant help.. others are a bit slow which I don't prefer... rest is up to u.. U get free manuals

Sounds like a fungus issue. Go to your local nursery and bring some plums.

Your county extension officer can offer a diagnosis for free, it appears to be an infection. Could just need a little TLC.

what do you mean, can you give some more details