Are your bushes looking a little… skeletal, this spring? There are a number of possible culprits, but we’ve been encountering one in particular this year: Sawflies!
What are Sawflies?
Sawflies are non-stinging members of the wasp family (Order Hymenoptera) that have caterpillar or slug-like larvae. Of these, 3 species in particular produce larva that enjoy chowing down on rose leaves – commonly referred to as Rose Slugs.
(Fun fact: The name “sawfly” comes from the saw-like, serrated appendage on the female wasp’s abdomen which she uses while laying her eggs on the undersides of host plants.)
What do Rose Slugs look Like?
There are 3 species of Rose Slug that may be your culprit: the European rose slug (Endelomyia aethiops), the Bristly rose slug (Cladius difformis), and the Curled rose sawfly (Allantus cinctus). Although their appearances vary somewhat, they are all primarily a light green color with an orange-ish head, and about 0.5-0.75 inches long at their biggest. These pests are often mistaken for caterpillars or slugs but there is an easy way to tell them apart: just count the pairs of legs! True Caterpillars have 2-5 pairs of protolegs, while Sawflies (rose slugs) will have 6 or more.
How do I know if I have Rose Slugs or something else?
Good question! Honestly, you can’t know for sure unless you catch them in the act – something that can be challenging to do with Rose slugs as they’re most active when it’s dark. However, their feeding patterns tend to be a fairly good indication. Rose slugs, particularly when young, chew away the tender top layer of the leaf, leaving behind a thin clear or brown layer of tissue and the veins. This is what we refer to as “skeletonizing.” As larvae mature, they begin to chew holes rather than simply skeletonize leaves.
How do I get rid of Rose Slugs?
As with most pests and diseases, the best method of protecting your roses is a proactive plan – start scouting for rose slugs in May- June. The slugs will be most active on the undersides of leaves during night time hours. If you find them, there are a couple things you can do to reduce/eliminate rose slugs from your roses:
- Pick them off by hand – Quickly removing and squishing rose slugs is a great way to ensure they can’t come back
- Dislodge with water – Rose slugs aren’t able to climb back into the foliage once knocked to the ground by water, making this an effective method of removal if you can find them all! Remember, they prefer to feed on the undersides of leaves.
- Mild horticultural oils/soaps – Neem Oil is a great example of this. These products coat the leaves in a thin, oily layer that interferes with insect feeding/movement, and is extremely effective when applied properly (read the label!).
- Insecticidal sprays – There are a number of insecticidal sprays approved for use on sawflies, but be careful when and where you spray them. The majority of insecticidal sprays, even mild ones, are acutely toxic to bees and are likely to kill other beneficial insects in the garden as well.
- Keep in Mind!! – Caterpillar sprays won’t work – as much as Rose slugs resemble caterpillars, they aren’t!
Does it matter which Rose Slug (Sawfly larvae) I have?
Yes and No.
Yes: In addition to their mild differences in appearance, the three species of sawfly have different numbers of generations each year and, depending on which species is making your rose bush it’s home, you could either be rid of them by July, or deal with them throughout the summer. The European rose slug (Endelomyia aethiops) has only 1 generation per year, while Bristly rose slug (Cladius difformis) and the Curled rose sawfly (Allantus cinctus) many have between 2 and 6, depending on weather conditions.
No: Management for each is the same.