Baytree Garden Centre’s tips on stopping Sawfly Larvae ruining your roses

In this week’s Baytree Garden Centre column, Mark Cox offers his top tips on tackling Sawfly Larvae on your roses…

While filling my face last week with burgers and sausages at a friend’s barbecue I was asked to take a look at their roses. So, with belly full and my once-white shirt now looking like a Jackson Pollock due to several large blobs of ketchup and mustard from aforementioned burgers and sausages, I felt that it was only fair to answer my hosts request and cast my expert eye over their roses.

I was completely taken aback by the scene of total devastation that awaited me. Large swaths of the plants’ foliage were missing, leaving just stalks and flower heads behind.

I could see hundreds of small, caterpillar-type creatures feasting themselves on the leaves and - to be fair - they were really enjoying tucking into this rose bush.

They weren’t actually caterpillars but in fact Sawfly Larvae. Sawfly Larvae get their name from the way in which the female adult insect uses her saw like egg laying appendage to cut into the young fleshy rose stems to which she then lays her eggs. When they hatch in early to late summer they are ravenous and devour pretty much all of the rose plant leaves that they can get their little teeth into.

It really is difficult to believe what these small greenish larvae with tiny black spots can do to a plant. Once the larvae have had their fill then burrow into the soil where they pupate and start the process all over again the following year.

Treatment can be handled in a number of ways, which I discussed with Jenny.

Option one is really quite simple - do nothing. The Rose Sawfly Larvae have evolved to eat just one thing – roses. In most cases as long as the rose its self is quite healthy it will tolerate some foliage loss.

Option two is a little more left field. By hanging Fat Balls that you would leave out for wild birds to feed on in and around your roses, you may well find that the birds landing on them will also decide that a few Sawfly Larvae would make a great amuse-bouche.

Option three is to go down the garden pesticide route. Now, with the real impact to the environment of garden pesticides now fully understood, many of the really active but sadly toxic ingredients are no longer allowed to be manufactured or used by law. That doesn’t mean that modern treatments are ineffective – but multiple applications are generally needed to tackle the problem. Bug Clear Ultra would be a great product to use at this point.

However, and here’s the big however, you really shouldn’t be spraying roses that are in full flower. The pesticide could be potentially harmful to bees and many other pollinating insects as they are very active at this time of the year.

So, the only option that I could really recommend to Jenny at this point is to pick the larvae off by hand when she sees them and encourage as many wild birds into her garden as she can to feed upon them. Next spring/summer, when the females lay their eggs again, look out for the telltale long-seeded scars in the plant stems and, with your nail or similar implement, squash the eggs.

With that I decided best to leave the stunned Jenny with her roses as I was sure someone had just said that dessert was about to be served and, by then, that was the only food stuff that I hadn’t spilled down my shirt!