Rose damage? Do this

Last week in this space I mentioned that Japanese beetles were just starting their feeding frenzy. Several readers responded by email alerting me to the fact that they seem to be scattered about the Miami Valley area.

In addition I talked about the flea beetles on various perennials, and, likewise, many of you responded that you are seeing the same damage.

Thanks to all for your feedback. I really appreciate this.

Several poeple also mentioned concerns with roses and the holes in the leaves and were wondering if the flea beetles were causing these holes.

The damage you are seeing on rose leaves is not likely caused by flea beetles but rather a complex of sawflies that feed on rose leaves. In fact, one man said that the leaves were destroyed.

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There are three sawflies that feed on rose leaves: European roseslug sawfly, curled roseslug sawfly and bristly roseslug sawfly.

First of all, these are not slugs. So put away the slug bait. It won’t work.

In addition, while they might look a little like tiny caterpillars, they are not controlled by Bacteria thuringiensis, a bacteria spray recommended for young caterpillars (but won’t control sawflies).

These are sawflies and can be a real pest on roses, causing significant damage. In years past, the damage has been moderate; this year I am seeing fairly heavy damage.

The European has one generation per year with the other two having two and three generations respectively. Therefore, you might see the damage all season long.

These sawflies “skeletonize” the leaves. They eat either the upper or lower surface of the leaf, depending on the species.

The bristly roseslug sawfly feeds on the lower leaf surface, leaving the upper surface intact. The result is sort of a “windowpane” appearance. There is a thin layer of tissue that remains on the leaf.

The curled roseslug sawfly gets to a point in their life cycle where they eat the entire leaf. I found these on my roses the other day.

All are tiny and all consume portions of the leaf. The result is a straggly looking rose.

Add to this the fact that you are likely seeing symptoms of the black spot fungus on roses and the overall appearance isn’t that nice.

If you are noticing damage throughout the season, it’s likely to be the bristly roseslug sawfly. Use topical applications of an insecticide that says on its label that says it controls sawflies.

Insecticidal soap will work as will any products containing carbaryl (e.g. Sevin), cyfluthrin (e.g. Bayer Advanced Vegetable and Garden Insect Spray) and bifenthrin (e.g. Hi-Yield Bug Blaster).

Make sure you spray the underside of the leaf surface, as this is where you will have the best luck in controlling them.

Products containing imidacloprid will be labeled for sawfly control but this product needs to be on the ground in April in order for the plant to absorb it to do the job. Use it early next season to prevent the problem.

Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at bennett.27@osu.edu.

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