Sawflies are a common garden pest that can quickly defoliate trees, shrubs, and other plants. These intriguing insects have a fascinating life cycle and appearance that resembles other bugs like flies, bees, and caterpillars. While sawflies generally won’t kill plants, heavy infestations can cause major damage and unsightly skeletonized foliage.

The good news is that with proper identification and well-timed organic treatments, you can get rid of sawflies and prevent future outbreaks. This guide covers everything you need to know about managing sawflies, from understanding their biology to implementing proven removal methods.

What Are Sawflies?

Sawflies belong to the insect order Hymenoptera, making them close relatives of bees, ants, and wasps. There are over 8000 species worldwide, with various types targeting specific plants. For example, the pine sawfly feeds exclusively on pine trees.

Unlike their stinging cousins, sawflies do not have narrow waists. Adult females also possess a serrated, saw-like ovipositor for depositing eggs inside plant tissues. This egg-laying apparatus gives the sawfly its name.

The larvae resemble caterpillars or slugs, depending on the species. They have three pairs of prominent thoracic legs, with additional prolegs on their abdomens. When disturbed, larvae may rear up into an S-shape. This defensive posture distinguishes them from true caterpillars like butterfly larvae.

Common examples of sawflies include the roseslug, pear slug, elm sawfly, and European pine sawfly. The larvae feed on plant leaves and needles, sometimes completely stripping them. Heavy defoliation can stunt growth, damage productivity, and injure the overall health of trees and shrubs.

Identifying Sawfly Infestations

The first step in controlling sawflies is learning to identify them. Carefully inspect the leaves and needles of susceptible plants during spring and early summer. This coincides with peak activity periods for the larvae.

Look for these signs of an active sawfly infestation:

• Clusters of small larvae on foliage. They may be lined up along leaf edges or entirely covering leaves.

• Leaves appearing skeletonized or lacy, with only veins remaining. This happens when larvae devour the softer tissue between veins.

• Curled, twisted, or rolled leaves. Some species inject fluids that cause leaves to contort protectively around eggs.

• Holes in leaves, or sections of leaves eaten away. This damage is similar to caterpillar feeding.

• Presence of adult sawflies. Look for black or patterned wasp-like insects that do not have pinched waists. However, the adults are rarely seen.

• White, green, or black larvae dropping from trees when disturbed. The larvae may hang from silk threads as they fall.

Pay special attention to the particular pattern of damage. Many sawfly species target specific plants, so identifying the host can provide clues about the pest. For example, skeletonized rose leaves may indicate roseslugs.

The Sawfly Life Cycle

Understanding the sawfly life cycle is key for well-timed management. Here is a brief overview of how sawflies develop:

Eggs - Adult females use their saw-like ovipositor to deposit eggs inside leaves, stems, or needles. The eggs are very small but may be visible upon close inspection, especially in conifers.

Larvae - After incubating for 1-8 weeks, the eggs hatch into larvae that immediately start feeding. Larvae pass through 4-6 instars over 2-8 weeks before reaching full size.

Prepupae - Mature larvae stop feeding and often drop into soil for protection. Here they transition into a prepupal stage.

Pupae - The prepupae form cocoons around themselves, entering the inactive pupal stage. This phase lasts for 2-3 weeks.

Adults - Adult sawflies emerge from pupae in the soil. After mating, females will lay eggs to begin the next generation.

Most sawfly species produce one or two generations per year. The prepupal stage allows many types to overwinter in the soil or leaf litter beneath host plants. Proper timing of control measures targets vulnerable larvae before they can hide underground and pupate into adults.

Non-Chemical Sawfly Control Methods

For mild or limited infestations, non-chemical methods can eliminate sawflies. Here are some effective organic options:

• Handpicking larvae - For lightly affected plants, manually removing larvae can provide sufficient control. Drop them into a bucket of soapy water. Wear gloves since some species can bite.

• Using high pressure water sprays - Strong blasts of water can dislodge larvae from foliage. Concentrate on undersides of leaves. Avoid excessive water pressure that risks damaging delicate plant tissues.

• Attracting natural predators - Birds, parasitic wasps, and predatory insects will feed on sawfly larvae. Creating habitat like birdhouses and pollinator gardens can increase their presence.

• Cultivating soil around plants - Digging up soil around host plants destroys overwintering prepupae and pupae. Do this in fall after larvae have dropped and again early spring before emergence.

For more severe sawfly infestations, the above methods may not suffice. Turning to natural insecticidal products can provide the intensity required while still sticking to organic growing principles.

Organic Sawfly Insecticides

Several OMRI-listed insecticides using natural active ingredients offer an organic way to kill sawfly larvae:

• Azadirachtin - Derived from neem oil, azadirachtin disrupts insect growth and deters feeding. Products containing this extract include AzaMax and AzaSol.

• Spinosad - This biological insecticide comes from a natural soil bacterium. When ingested, it causes paralysis and death in sawfly larvae. Look for products like Monterey Garden Insect Spray.

• Beauveria bassiana - A fungus that infects larval sawflies and kills them within 3-5 days. Available as BotaniGard ES or Mycotrol ESO.

• Pyrethrins - Extracted from chrysanthemum flowers, pyrethrins attack the nervous system of insects. Safer Brand and other companies sell garden products containing pyrethrins.

• Insecticidal soaps - Potassium salts of fatty acids disrupt cell membranes upon direct contact. Look for concentrated formulas that allow dilution for cost-effective coverage.

• Diatomaceous earth - The sharp edges of this powdered fossilized algae damage the exoskeleton and cause dehydration in larvae. Avoid DE formulations with added synthetic insecticides.

Always follow label directions for these organic insecticides. Thorough coverage of foliage is vital for successful sawfly control. Reapply initially after 5-7 days and then every 1-2 weeks while larvae remain active. Rotate between different products to reduce resistance.

Conventional Sawfly Insecticides

While organic options are ideal, conventional insecticides also kill sawfly larvae effectively:

• Carbaryl - Sold as Sevin and other brands, this cholinesterase inhibitor is toxic to a wide range of insects. It can be applied as a spray, dust, or systemic soil drench.

• Malathion - Derived organophosphates disable the nervous system in insects upon contact. However, malathion is also highly toxic to bees and aquatic life. Exercise extreme caution when using.

• Permethrin - A synthetic pyrethroid that works as both contact and ingestion insecticide. Formulated into many retail garden products for ornamental pest control.

• Bifenthrin - Similar to permethrin, this neurotoxic pyrethroid is available in ready-to-use concentrates and premixed sprays. Ortho Bug-B-Gon contains bifenthrin.

While fast-acting, synthetic insecticides have risks like insect resistance, plant damage, and hazards to pollinators or pets. They also offer no residual control. Weigh these factors carefully when considering conventional chemicals for sawfly issues.

Preventing Future Sawfly Infestations

After eliminating an existing infestation, take steps to prevent future sawfly problems:

• Maintain vigilant monitoring of susceptible plants during early spring when larvae first emerge. Take quick action at the first signs of sawflies each season.

• Encourage predatory beneficial insects like ladybugs and green lacewings with nectar plants and limited pesticide use. They will help keep sawfly populations in check.

• Use reflective mulches like aluminum foil around plant bases. The reflected light and heat can deter females from laying eggs on lower leaves and needles.

• Prune trees and shrubs to promote airflow and make them less favorable for sawflies. Remove any branches, twigs, or stems heavily infested.

• Water vulnerable plants during early morning instead of evening. This helps reduce humidity levels that favor sawfly egg laying and development.

• Apply organic insecticides early in spring before eggs hatch or damage appears. Use horticultural oils and neem treatments proactively.

With diligence, prevention reduces the need for intensive sawfly treatments season after season. Quickly catching any renewed outbreaks also keeps populations contained before they explode.

Conclusion

Controlling pesky sawflies takes some persistence, but eco-friendly methods let you protect plants without resorting to dangerous pesticides. Start by properly identifying the particular species affecting your trees, shrubs, or flowers. Sawfly larvae are most vulnerable when young before burrowing into soil. Knock them off with blasts of water or apply natural insecticidal soaps or oils during this stage. For severe infestations, use OMRI-listed organic insecticides derived from plants, minerals, or microbes. Avoid overuse of harmful synthetic chemicals which pose risks to people, pets, and beneficial insects. With observation and early intervention each season, you can keep sawflies in check and your garden foliage in top condition using safe organic practices.