I bought a house last fall that has lovely raspberries growing on the north side of the house with lilies-of-the-valley growing underneath. In early summer, I noticed that the lilies-of-the-valley were turning brown and later in the season I noticed my blackberry bush developed brown spots on all the leaves. How can I prevent this is the future?
Both plants are suffering from fungal diseases. Though the symptoms look similar the cause and control is different. Let’s start with the lily-of-the-valley. Remove infected leaves and stems as they appear. This is usually enough to keep the disease under control. The raspberries are probably suffering from a different fungal disease known as anthracnose. Proper pruning will help keep this disease under control. This winter remove any old canes that bore fruit. They are done bearing and their presence only increases the risk of disease. Then thin the canes to about 5 to 6 per foot within the rows. In the future, remove and destroy all canes that bore fruit right after harvest. Then do any needed thinning in late winter. Proper pruning increase air circulation and light penetration to the planting. This means more fruit and fewer disease problems.