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Raspberry sawfly

The raspberry sawfly (Monophadnoides geniculatus) is a small, black, wasp-like insect that appears in early summer. The female lays eggs on the leaves of primocanes. The larvae are small and green and look like little caterpillars. They feed on the leaves, while avoiding the larger veins. The result is a leaf that is peppered with small holes, creating a distinct netted look, a type of feeding referred to as skeletonizing. Be sure to look for the presence of the sawflies as this damage could be confused with Japanese beetles. Sawflies have one generation per year.

Damage

The skeletonizing done by sawflies can look serious on canes where an adult laid multiple eggs, but raspberry sawflies rarely causes a loss in yield. Typically, only a small number of canes have sawfly larvae. The damage only occurs in early summer. Individual primocanes can often outgrow the damage. Gardeners may find the middle of canes with damaged leaves, while the tops and bottoms of the same canes have normal, healthy leaves.

Management

Sawflies rarely need to be managed in Minnesota. In small patches with minor infestations, the larvae can be removed by hand. If the majority of primocanes have sawfly damage, an insecticide may be necessary. Only spray insecticides if the little pale green "worms" are visible and still feeding on the leaves. If there are no worms, and the cane is forming healthy new leaves above the skeletonized leaves, the larvae may already be gone. Sawfly larvae are susceptible to 'soft' insecticides, such as insecticidal soap. Contact residual insecticides such as permethrin, malathion and carbaryl are also options.


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