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Habitual Gardener

Promoting healthy garden habits and habitats
dogwood sawfly2forweb

What's Devouring my Dogwood?

Redtwig dogwoods typically grow with wild abandon despite a few insect (scale) and disease (twig canker) problems. As North American natives redtwigs have their share of North American native insects that enjoy them for lunch, (and breakfast and dinner). This year my redtwig dogwoods had a bit extra bling in August and September. The vivid white dogwood sawfly larvae hung like earrings on the leaves. The larvae look like caterpillars, but their parents are neither moth nor butterfly. Female adult dogwood sawfly is black and wasp-like and can lay hundreds of eggs. Luckily there is only one generation a year. The white larvae with their dark spots and yellow bellies are really quite pretty. However I suspect pretty is not the goal. They are likely attempting to hide in plain sight by mimicking bird droppings. Larvae damage leaves by eating all but the veins. Leaves stay on the plants as mere skeletons. Once larvae finish feeding in late September or early October they wander to find a place to pupate and spend the winter typically in rotting wood. In addition they can annoyingly use wood siding or landscape timbers.

If control is a concern, summer oils and insecticidal soaps work well while larvae are feeding. Since they are not caterpillars, Btk products for caterpillar control do not affect sawflies. As larvae age chemical control is less effective and squishing them with the bottle would be more effective. My redtwig dogwoods are so vigorous and the sawfly defoliation comes so late in the season that I choose to let the sawflies feed away and I enjoy the late summer bling.

How do you tell the difference between sawfly larvae and caterpillars? You have to get up close and personal. Both have 3 sets of true legs right behind the head; however, the number of pairs of prolegs (those toward the tail end including the anal claspers) are different. Sawfly larvae have 6 or more pairs and caterpillars have 5 or less pairs. Caterpillars always have anal claspers while sawfly larvae may or may not have anal claspers. Check out this great info from Missouri Botanical Gardens.

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