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I was having a walk around our Lottie site and notice lots of raspberry bush turning yellow ,mine are fine just now ,is this a virus or something else ?

I have had some yellowing in past years and had some success by using Sequestered Iron (Sequestrene) which causes the new leaves to grow green.  Apperently rasps can suffer from trace element deficiencies which includes Iron, Manganese and Magnesium which all cause leaf yellowing.  If it is viruses causing the problem then the plants will probably go downhill steadily.  Useful data here:

http://www.gardenersworld.com/how-to/problems/fruit-and-nuts/raspberry-nutrient-deficiency/440.html