Rose bushes bring a beguiling and elegant presence to any your home garden. Unfortunately, drought, improper soil pH or lack of nutrients weakens their vitality and leaves them susceptible to insect infestation. Early detection is the key to preventing irreversible damage and avoiding the need for pesticides that harm blossoms and kill beneficial insects.
"Sawfly larvae skeletonise rose leaves," according to the University of Minnesota Extension Service. They belong to the order Hymenoptera, which includes bees and wasps. Three species of sawflies roseslug (Endelomyia aethiops), bristly roseslug (Cladius difformis) and curled rose sawfly (Allantus cinctus) create green caterpillar lookalike larvae that defoliate your rosebush leaf by leaf and leave only a skeleton of veins behind. The adults are little, dark coloured, non-stinging wasps. Organically control sawflies and remove them by hand. For squeamish gardeners, knock the insects off the plants using the garden hose in the early morning.
Japanese and False Japanese Beetles
Both the Japanese (Popillia japonica) and false Japanese beetles (Strigoderma arbicola) are of the scarab variety and eat rose bushes. Japanese beetles eat foliage and flowers. Adult false Japanese beetles dine on the buds and flowers, while their larvae feast on the roots. Both species of beetles grow to a length of 10mm to 12mm, and have a metallic green colour, though the Japanese beetle is a more brilliant green. To positively identify a beetle, the other University of Minnesota Extension notes that the Japanese beetle has, "five small, white patches of short hairs along each side of the dorsal abdomen on the beetle. These patches are a key characteristic for identification." As with the sawflies, manually removing them or spraying them with a garden hose is superior to chemical pesticides, which can damage flowers and kill bees.
Fuller Rose Beetle
Known as the fuller rose beetle (Asynonychus godmani), this little rose bush-eating pest is actually a weevil. Larger than the Japanese and false Japanese beetle, adults grow to 14mm or 15mm. They have a brown colour with mottled black markings. Each life cycle of the fuller rose beetle attacks rose bushes. Adults chew on leaves and flowers, while the larvae make their meal from the roots. To control fuller rose beetles, the University of Minnesota extension advises, "Hand picking at night is an option with low populations."
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