Raspberry Cane Blight
Cane blight is a common fungal disease of raspberries (Rubus sp.), which can destroy your crop if it is left untreated, it will spread from one plant to your whole raspberry patch. Fortunately the disease is fairly easy to prevent, and even easier to treat.
Cane blight may cause your berries to become small and hard, and not mature properly. You may also notice that the leaves become pale in color, and may even turn yellow. Dieback will occur at the top of the canes and move downward. The bark may become gray, or covered with black spots. It will then begin to peel away from the wood of the cane. These symptoms will most likely occur on older canes first, which is why it is so important to prune out old canes yearly.
To treat cane-blight, you must prune the infected canes back to the ground, and then dust them with sulfur dust. The sulfur dust will prevent the infection from reoccurring.
To avoid the need to prune back your plants, you will need to care for your raspberries properly, in a way that will prevent cane-blight. Growing your plants in ideal conditions is the best way to prevent any disease. So make sure that your raspberries are fed and watered properly. A fertilizer such as 15-30-15 will keep the plants strong, and encourage flowering, and fruiting. Watering the plants in the morning is the best time because this allows plenty of time for the plants to dry off before the sun is set and the temperature drops. If this is not possible, water the plants in the late afternoon, or very early evening. You want to make sure that you give them enough time to dry off before nightfall. Another important thing is to remove all canes that are three years old. This will encourage new growth, and thin out the bush to reduce overcrowding and increase air movement. This is also important because in most cases it is the older canes, which first develop cane-blight. Removing any weeds and dead plant material will also increase air movement, reducing the chances of infection. Infection may also be introduced through wounds caused by insects and garden tools, so keep watch for harmful insects, and sterilize your pruning tools in a solution of one part Javex to nine parts water.