Certified GKH Gardening Expert
There are a number of reasons for this. If the leaves are yellow with green veins, the raspberry plant is suffering from an iron deficiency, or chlorosis. Here is more information: https://www.gardeningknowhow.com/plant-problems/environmental/leaf-chlorosis-and-iron.htm Mottled leaf yellowing, stunted growth, leaf blisters and brown tips on leaves may indicate Raspberry mosaic. It is also possible that it is a fungus, in which case you can try a fungicide. Pests are often associated with yellowing of plants. Neem oil can be used for treating both pests and fungal issues. Finally, check your drainage. Ensure that the soil around the plants is not overly saturated, which could lead to root rot.