Blackberry plants are highly valued for their sweet fruit, but damaged foliage can quickly turn anticipation into frustration. Successfully addressing leaf damage requires accurate identification, as the appropriate solution depends entirely on the specific culprit. Examining the visual evidence on the leaves allows gardeners to narrow down the possibilities and implement a targeted remedy.
Decoding the Damage Patterns
Diagnosing the problem begins by categorizing the visual appearance of the leaf damage. One common pattern is skeletonizing, where the soft tissue is consumed, leaving only the tougher, vein-like structure intact, often creating a lacy or window-pane effect. This contrasts with clean-cut holes, which appear as distinct, circular or irregular perforations that pass entirely through the leaf blade. Other signs include leaves that look ripped or torn, resulting in a ragged edge. When a leaf appears rolled or tied together with fine silk, this indicates a pest is using the foliage as a protective shelter while it feeds.
If entire shoots or large sections of leaves are missing, the damage is likely caused by a larger animal capable of browsing significant amounts of plant material quickly.
Identifying the Primary Insect Pests
The most frequent insect culprits causing chewing damage are the Japanese beetle and the raspberry sawfly. Adult Japanese beetles (Popillia japonica) are recognizable by their metallic green bodies and copper-brown wing covers, measuring about half an inch long. These beetles feed in groups during the summer months, creating the characteristic skeletonized leaf appearance by consuming the tissue between the veins. Sawfly larvae (Monophadnoides rubi) are also significant defoliators, appearing pale green with small, bristle-like spines. They are often found feeding on the underside of young primocane leaves, causing extensive skeletonizing damage and irregular holes.
Another common pest is the leafroller, the larval stage of various small moths. These caterpillars protect themselves by spinning silk to fold or tie the leaf around their body while they feed. This action causes the leaf to become distorted and perforated.
When the Culprit Isn’t an Insect
If large sections of leaves or entire young canes have been cleanly clipped or browsed, the culprits are likely rabbits or deer. Rabbits typically make a sharp, clean cut when they feed, while deer tend to rip and tear the foliage, leaving a ragged edge on the remaining stem. Deer can browse up to six feet high, whereas rabbit feeding is generally limited to two feet or less above the ground.
Mollusks such as slugs and snails also cause significant leaf damage, often creating large, irregular holes, particularly on lower leaves near the soil. The tell-tale sign of a mollusk is the presence of a silvery slime trail left behind on the foliage. Damage that appears as spots or lesions rather than actual chewing is often a symptom of a fungal issue, such as leaf spot. This disease presents as purplish spots that develop tan or white centers, sometimes leading to premature leaf drop.
Targeted Solutions for Leaf Damage
For the Japanese beetle, manual removal is often the most effective non-chemical option. This involves shaking the sluggish morning beetles into a bucket of soapy water for disposal. If the problem is sawfly larvae or a leafroller caterpillar, the biological insecticide Bacillus thuringiensis subspecies kurstaki (Btk) can be applied. Btk specifically targets and eliminates chewing caterpillars without harming beneficial insects.
In the case of general insect feeding, organic sprays like insecticidal soap or neem oil can be used to control soft-bodied pests. For vertebrate pests like deer and rabbits, physical exclusion is the most reliable method. This requires the installation of a sturdy fence or fine-mesh netting over the canes. Managing fungal diseases requires improving air circulation through proper pruning and avoiding overhead watering.