Rose slugs are not true bugs but the larvae of the sawflies that belong to the family Tenthredinidae and have a place under the Order Hymenoptera. These are common sawflies with bristly appearance, and their several generations could produce in a year. Upon heavy infestations, they can damage strawberries and raspberries besides their native host. i.e., Roses. Rose slugs feed on the surface of leaves and remove their soft tissues leaving behind only the veins. Heavy infestation sometimes leads to excessive defoliation, and foliage appears burnt. The result could be the semi-transparent and ragged leaves and deformed roses on the bush with low market acceptability.
Sawflies originated from Eurasia and North America but, were accidentally introduced to temperate, tropical, subtropical, and arctic North America. Most of the Rose slug species were first recorded from eastern states with the planting materials. Some species were also simultaneously introduced on the west coast. Now, rose slugs are evenly distributed through most of the North American nurseries, gardens, and landscapes and have become a pest of concern for the gardeners. Otherwise, rose slugs are found throughout the US in all sorts of growing cultures.
The species in focus is a bristly rose slug that contains fine hairy spines on the green or yellow-green body and could grow nearly 3/4 inches in length. Rose slug also secretes a slimy material from their bodies that resemble the slugs. However, they're not slugs instead of the larvae of sawflies. Rose slugs feed on the leaves of the roses besides on plum, cherries, strawberries, and raspberries. The color of an adult rose slug could range from black to green orange and striped yellow. Often, the adult rose slugs are black with two pairs of dull black transparent wings, and their body measuring between 4 to 5 mm long. Their emergence in the gardens is often during early to mid-summer.
Adult rose slugs can appear in early spring that will be ready to lay eggs on the undersides of the leaves of the rose shrubs. A larva may take another month to appear and could start feeding on the tender leaf tissues for about a month and migrate to the surface soil for pupation. There may be several generations of rose slug per year as they produce two to six generations before going into pupation. Generally, the offsprings that emerge in mid to late summer are most abundant. Fully developed larvae stop feeding on the foliage in fall and overwinter in cocoons in the soil before appearing again in early or late spring.
Rose slug is host-specific and harms strawberries, raspberries, and a few other plant species but, the prevalent damages may be noticed on rose shrubs only. Often, they feed on the lower surfaces of the rose shrubs eating the entire soft tissues and leaving behind the veins only. This makes the leaves appear shining and papery. Heavy defoliation weakens the rose shrubs and could diminish their ability to photosynthesize. Generally, the light to the moderate presence of rose slugs is acceptable. However, a heavier infestation could lead to deformed flowers reducing their market acceptability. Additionally, the stressed leaves could fall prey to several other fungal diseases and become susceptible to a variety of garden pests as well.
Whenever the growing conditions become adaptable, its' time for the Rose slugs to emerge from the cocoons that have overwintered in the garden soil or plant debris beneath the plant's canopy. These conditions start in the early to late spring depending on the temperature and humidity level in different gardens. When the active feeding starts, rose slugs can be noticed on the undersides of the leaves, and this is the best time to make necessary arrangements to check their further infestations in the garden. Generally, rose slugs are not a threat for the gardeners if the infestations are lower. However, heavy infestations could become cultural and insecticidal remedies to control them.
Besides following all preventive measures if Rose slug infestations go beyond your control, here are the most authentic ways to keep their population suppressed using the biological, organic, and chemical methodologies;
Green lacewings are an unappreciated class of predatory insects that, in combination with lady beetle predate many species of soft-bodied insects and their eggs. These insects sometimes exist naturally in the spring, summer, and fall, and their role in insect pests control is vast. Green lacewings feed on the rose slugs during their larval stages and eggs. They may be released in combination with Trichogramma species if the infestations are complex. Green Lacewing is also friendly with Praying Mantis. 1000 Green Lacewings are enough for 2500 square feet when released in the garden.
These eggs hatch in almost 4 or 5 days. Release them immediately after they hatch their population before rose slugs establish in any landscape.
Lady Bird Beetles are also an exceptional group of predatory bugs that feed on many soft-bodied pests that often harm the foliage of the plants. When applied on the garden beds, they don’t control only rose slugs but several other slow-moving pests that gardeners often neglect due to their smaller size. Lady Beetles also feed on whiteflies, aphids, thrips, leaf miners, and mites. However, they can't feed on the insects that fly. On releasing live bugs or allowing their eggs to hatch in the garden, lady beetles are ready to prey on their target insect pests in about 7-days.
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Wash the surfaces of the leaves with splashing water and release ladybugs afterward. Almost 1500 live bugs are enough for controlling many pest species including, rose slugs in 1000 square feet of garden area.
Bonide- Caterpillars and Worm Killer contains 9.83% of Bacillus Thuringiensis-Kurstaki strain, and 1-milligram of concentrate consists of almost 6 million active spores with cry proteins. Bacillus thuringiensis is a soil-living bacterium that produces crystal proteins that bind with the mid-gut of targeted pests and rupture it. It also parasitizes rose slugs and larvae of many other damaging pests. BT is the same organism that is used in modern days GMO crops such as BT cotton, and BT corn. This product is also OMRI listed and can be used on a variety of edible plants, including vegetables, fruits, and flowers.
It comes in a ready-to-use formulation, and no further mixing in water is required.
Natria- Neem oil comes in two types of formulations. The one that uses 70% active ingredient needs mixing in water, and the other is 0.9% Clarified hydrophobic extract. Neem oils contain Azadirachtin, and their ovicidal activity against some Dipteran species is readily established. However, it's a broad-spectrum insecticide that is a feeding deterrent, fungicide, sterility inducer, and insect growth regulator together. Moreover, it controls many insects from more than 6-insect Orders. Natria is effective against rose slugs when applied during early larval growth. The product is highly recommended in organic gardening for many insect pest complexes. It is also OMRI listed and can be used on edible plants to the day of harvest.
Apply it directly on the foliage if it is ready to use product. Otherwise, mix 2 ounces of the product concentrate per gallon of water when the active ingredient is 70% Neem oil.
Safari contains 20% Dinotefuran which is a newly developed insecticide of the neonicotinoid class. Its mode of action involves disrupting the insect's nervous system by inhibiting nicotinic acetylcholine receptors. It is applied to kill rose slugs besides aphids, whiteflies, leafhoppers, sawflies, and mealybugs on leafy vegetables growing indoors and turfgrasses pests. The best application involves soil drenching to reduce the harm to beneficial insects. Also, avoid applications during flowering to save honeybees and pollinators.
Try to avoid foliage applications due to a higher level of toxicity. For soil drenching, mix between 5 to 8 ml of concentrate per gallon of water and apply heavy irrigation afterward.
Check out our other guides on common garden bugs.
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