July is raspberry season. But you might have noticed some damage on your raspberry canes. Two common problems you'll see this time of year are raspberry cane blight and raspberry tip borer. Although neither problem will wipe out your raspberry crop, they both will reduce your yields.
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If you see random fruiting canes dying back, check for areas of purple or black on the stems. They may have a fungal blight. This blight starts on the first year canes and overwinters. During the second season, as the canes start to fruit, the blight blocks off the flow of water and nutrients from the roots and the cane dies. The best controls for cane blight are trying not to damage first year canes. Wounds are the opening blight needs to get established. Remove any infected canes as soon as possible and bury them. Don't prune during wet weather. Prune your second year old canes to the ground as soon as they're finished producing. Thin overwintering canes in early spring so they're spaced at least 6 inches apart to promote good air flow.
If you notice the tips of new canes wilting, you may have the cane tip borer. This insect lays a small egg in the cane, then girdles the cane above and below where the egg is laid. This causes the cane tip to wilt. It's easy to spot the wilting, and the girdling, on the young, green canes. Prune off any infected canes below the lower girdle line and destroy them. Since you're just removing the cane tip, the plant should grow fine and still produce next year.