Large Rose Sawfly
Large Rose Sawfly
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The Large Rose Sawfly (Arge pagana) is a fly-like insect possessing a shiny black body and bright yellow-orange abdomen. Sawflies are close relatives of wasps, bees and ants. The adults are pollinators, feeding on the pollen and nectar during the day. The adult sawflies can damage the stems as a result of egg-laying, which may result in split, weak stems. The larvae are the most problematic. They look very similar to caterpillars, feeding on the leaves of Roses. They can quickly defoliate plants, leaving behind unsightly irregular sized holes.
Can weaken the stems of rose plants.
The adults are garden pollinators.
Adults: Adults are sometimes mistaken for a large fly or wasp (length approx: 1cm). They have bright yellow-orange abdomens, tinted black-grey wings, with black shiny bodies. Larvae: The larvae look very similar to caterpillars. They can grow up to 2.5cm total. They possess yellow heads with light yellow-green bodies, covered in black spots. Larvae may appear shiny or slimy. Eggs: The eggs are yellow, ovular in shape and laid within plant stems, so can be difficult to detect.
Stems of roses may split. Numerous green, spotty worms/ caterpillars on Rose leaves. Larvae make 'S' shape when disturbed. Rose leaves can be stripped. Heavy infestations can kill smaller plants. Windowpaning of leaves. Irregular sized holes throughout leaves. Damage appears similar to that of a Japanese beetle.
The UK, some parts of Europe and the USA
Larvae can be removed by hand and disposed of. If you come across eggs on your stems, you can also destroy these by either cutting away the stems and disposing of them or trying to scrape the eggs off, making sure to get them all. For large infestations, another tip for removing larvae would be to spray down plants and trees with a power hose. Place a white towel or sheet below plants to ensure all larvae are collected and relocated or disposed of. Neem or spinosad can be effective. Similarly, homemade or store-bought insecticidal soaps and horticultural oils are thought to offer some protection if your infestation is moderate to severe. If infestations are caught early, no product should need to be used at all. Restrict applications to cooler parts of the day, taking care not to spray any flowering plants. Please read bottle label instructions prior to application. Birds, frogs, lizards and parasitic flies and wasps will prey upon sawfly adults and larvae. Attract these into your garden by allowing areas to grow a little wild, or mow and trim back plants less often. Hanging baskets, climbing plants and log piles are great spaces for beneficial wildlife to take cover during the day.
You can spray plants with pesticides if you have an infestation that is too large to remove by hand, it is best to do this at dusk when the caterpillars are more active. You should not spray plants that are in flower, because this harms some pollinating insects. There are an array of contact insecticides available for use on the market that is more environmentally friendly than the above products (e.g. Natural pyrethrum/pyrethrins and insecticidal soaps). More persistent products include synthetic insecticides with a contact mode of action (e.g. cypermethrin, phenothrin, lambda-cyhalothrin and deltamethrin). Please take care to research products and read instructions carefully before using them. Please think of the severity of an infestation and the time of year before opting for one of the above treatments.