Fertilizing heritage raspberries
Hard to say from the description if it is a fertility issue, soil problem or disease. Fertilizer applications are usually based on soil or tissue tests to see which nutrients are deficient and which are abundant. Nitrogen or potash are the most likely nutrients necessary.
Annual nitrogen applications for primocane bearing raspberries are about 80 pounds of actual nitrogen per acre of raspberries. This application should be split into 2 equal applications, one in the early spring and the second in the mid season after the primocanes are about 2 to 3 feet in height. Sand soils may require more fertilizer because the soil holds less.
Annual application of 50 to 100 pounds of actual potassium may be necessary especially in sand soils. This application should take place in the early spring.