[allotmentann]

Hello Stelios and welcome to the site
Goji berries fruit on last years stems. The RHS advice is to prune it lightly in spring to remove any diseased or badly placed branches and to take out some of the older wood - I assume that means wood over two years old.
http://apps.rhs.org.uk/advicesearch/Profile.aspx?pid=581

[stelios]

i would like to thank you for your usefull information,but when a tree is dry, without leaves is certainly sucker on plant?because i have 5 trees dry,without leaves,but the trunk is alive

[allotmentann]

I am sorry I do not quite understand what you are asking? Are you asking about your Goji berries or something else?
Perhaps you could tell us where you are? Are you in the UK? It is autumn here and most trees have very few leaves at the minute or none at all. Or are you asking if your tree is diseased?

[stelios]

  sorry,in this url that you have send me i saw something for a disease (sucker disease) and i have 5 trees with no leaves and other plants have fruit,i am asking you for what these trees are badly? I live in Greece and the temperature here is from 25c -to 15c and the weather is sunny

[allotmentann]

No, suckers are not a disease, they can be a way that a plant makes new plants. They are stems that gow from the bottom of a plant. Some plants make lots and lots of these which can be a problem (not a disease) and so you need to cut some down to the ground.

[stelios]

thanks!