Willow Sawfly Control

What Insecticides Kill Sawfly Larvae

Willow Sawfly Control-a-sawfly-larvae
A sawfly Larvae

Nematus oligospilus commonly known as the willow sawfly is a garden pest in the species of the sawfly family Tenthredinidae. The willow sawfly is a non-stinging member related to the wasps. This insect is native to central and northern Europe and Asia. These sawflies are most active during the spring months and mid-summer, feeding on the willow tree.

What makes the larvae of this sawfly so dangerous is that large populations can actually kill the trees over time. The willow tree however comprises about 350 species of typically deciduous trees and shrubs. These trees can be found growing primarily on moist soils in cold and temperate regions.

Willow Sawfly Biology

The lifecycle of the willow sawfly from egg to adult is completed in 20 to 30 days during the summer months. These wasps are most often seen during the larval stage where feeding damage can be seen on the plant’s leaves.

The eggs are cream-colored and laid by the female (sawfly) on the underside of the plant’s leaves, leaving a visible blister once the larva hatches, the eggs are 1-2 mm long. The larvae enter dormancy in May or about 4 months and then emerge as an adult from the cocoon in October. What’s interesting is that several generations can occur in a single season. The larvae can be identified by a lime green color and large blackheads, as they grow becoming a large bright green/yellow larvae with distinctive stripes of black markings. The adult sawflies are 5 to 5.7 mm long, dark- copper color flying insects with two pairs of wings.

Signs of the Willow Sawfly

As the larva of the willow sawfly emerges it eats a window in the leaf and then begins to feed along the edge of the hole. Once the larvae molt it usually moves to the edge of the leaf and continues to feed. A single larvae can consume several entire leaves, the larvae are vigorous defoliators and can cause complete defoliation of young or ornamental trees. A few species of sawflies can also leave galls on the foliage.

How do Leaf Galls Look

Willow Sawfly Control-leaf-gall
Leaf Gall

The area of the plant’s flesh develops a scabbing area, bump, or peak, these affected areas are firm to the touch can thickly coat a plant, and can be found singly or in pairs. Leaf galls may even have the appearance of pimples, can be bright pink or red, and can be green looking like a part of the plant. Galls will not necessarily harm plants but can reduce a plant’s beauty. Treatments for leaf gall are not really recommended because the application of chemicals can do more harm than good.

Preventive measures to avoid leaf gall are to go ahead and give your plants and application of miticide, other insecticides including horticultural oils is effective but not after the mites are under the surface of the plants.  Avoid the use of broad-spectrum insecticides which can harm potential predators of the gall mite,

The proper maintenance of a plant’s health can help to prevent gall mites, try to avoid damaging the stems and the trunks of trees which could encourage the presence of insects, fungal or, bacterial diseases.

Note: The most effective way to discourage leaf gall is to choose plants that are resistant to the most prevalent varieties in your zone or region.

How to Control the Willow Sawfly

There are several ways to control willow sawflies one way is mechanical control, this method involves hand-picking the caterpillars or larvae and throwing them into a bucket or container of soapy water. Another method is to catch the larvae stage at the beginning of the feeding prune or clip of infested stem or foliage if larvae are on the inside of a small portion of the plant.

How to Deter the Willow Sawfly

During the winter months, the willow sawfly overwinters in the soil, and an effective method to eliminate them without the use of chemicals is to dig around the willow tree. This will expose them to the winter freeze killing them off.

Controlling Willow Sawfly with Insecticides

Note: Before using chemicals or insecticides read and follow the manufacturer’s direction for the best results, Below are a listed group of pesticides that can be used.

  • Diazinon
  • Malathion
  • Carbarly
  • Monterey® Garden Insect Spray (Spinosad)
  • Insecticidal Soap
  • Neem Oil
  • Narrow-range Oil

Note: Before and after the application of chemicals keep kids and pets out of treated areas.

In Case you missed it here are other articles on different species of sawflies and how to bring control.

The final word on willow sawfly control

This guide has shown effective measures to control this garden insect pest, the willow sawfly can become a danger if the damage effect or high populations are present. The good news is with some work you can help your plant to bounce back to good health and retain its beauty or you can catch this pest early in its stage and strike back. Following this guide will bring the results you’re looking for.


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About the author

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Norman loves being in the garden, both at home and for his job....
he is 'Natures Little helper' being outdoors, growing his vegetables and flowers from an early age.
Now having spent over 22 years in the profession he want to give some of his knowledge to others...
his vast array of hints and tips you will find scattered over this site will help you no end growing plants in your garden.

2 thoughts on “Willow Sawfly Control”

  1. Hi, identifying effective insecticides to combat sawfly larvae can be crucial for protecting plants and trees. I’m curious, are there specific insecticides or organic alternatives that you recommend for targeting sawfly larvae? Additionally, do you have any tips on the timing and application methods to maximize the effectiveness of these treatments while minimizing environmental impact?


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