Is this sawfly damage? - Ask Extension
The damage is on lemon drop evening primrose that has been in this bed for around ten years. And is there anything I can do to save them? The larvae a...
Knowledgebase
Is this sawfly damage? #831761
Asked May 24, 2023, 8:48 AM EDT
The damage is on lemon drop evening primrose that has been in this bed for around ten years. And is there anything I can do to save them? The larvae are way too tiny to pick off.
Charles County Maryland
Expert Response
There is at least one sawfly species (we think native, though there is little info. about them we could find) that feeds on Evening Primrose. The photo of the larva is not in focus but it does generally look like it could belong to a sawfly. Fortunately, these plants tend to be so vigorous that any temporary defoliation caused by these larvae should not kill the plants; they should eventually produce new growth to replace what was lost.
Given that this seems to be a native insect and is valuable as a prey item to other wildlife, and given that the long-term health of the plants is probably not under threat, we do not recommend an insecticide. You could cut the plants back if too unsightly, but this might delay regrowth and reblooming as the plants would have to replace the removed stems as well instead of just the foliage chewed off the stem. Given how much damage has already been done, the larvae are probably almost finished feeding and will then mature into adults that won't damage the plant; there's also little that would be able to be sprayed with a pesticide anyway since most of the foliage is missing.
If you feel you must intervene, then either cut the plants down to force regrowth (dispose of the clippings in yard waste or a compost pile) or treat what is left with a lower-toxicity insecticide like horticultural oil or insecticidal soap. Follow all label directions on the product about dosage and when to re-apply. Be aware that such products require thorough coverage of the foliage (tops and bottoms of leaves) because they have to literally contact the insects in order to affect them (dried spray residues on the foliage will not be effective). Since this can be hard to spray well on low-growing plants unless you can bend them over to hit the leaf undersides without breaking the stems, this is one reason it's simpler to forego pesticide use and just physically remove them, allow them to complete their life cycle, or to do the pruning we mentioned above.
Miri
Given that this seems to be a native insect and is valuable as a prey item to other wildlife, and given that the long-term health of the plants is probably not under threat, we do not recommend an insecticide. You could cut the plants back if too unsightly, but this might delay regrowth and reblooming as the plants would have to replace the removed stems as well instead of just the foliage chewed off the stem. Given how much damage has already been done, the larvae are probably almost finished feeding and will then mature into adults that won't damage the plant; there's also little that would be able to be sprayed with a pesticide anyway since most of the foliage is missing.
If you feel you must intervene, then either cut the plants down to force regrowth (dispose of the clippings in yard waste or a compost pile) or treat what is left with a lower-toxicity insecticide like horticultural oil or insecticidal soap. Follow all label directions on the product about dosage and when to re-apply. Be aware that such products require thorough coverage of the foliage (tops and bottoms of leaves) because they have to literally contact the insects in order to affect them (dried spray residues on the foliage will not be effective). Since this can be hard to spray well on low-growing plants unless you can bend them over to hit the leaf undersides without breaking the stems, this is one reason it's simpler to forego pesticide use and just physically remove them, allow them to complete their life cycle, or to do the pruning we mentioned above.
Miri
Thank you very much. I'm perfectly happy with the "do nothing" recommendation...
You're welcome.
