If you’ve ever had to contend with sawflies in the garden, you know what a headache these pests can be. One day your plant’s leaves are looking green and robust. Then, without warning, you’ve got ugly, brown, chewed-up leaves all over the place. In my garden, the zinnias are the most likely victims.
Sawflies, and more specifically, their larvae, can be incredibly destructive in the garden. Fortunately, with a little knowledge of how these insects function, we can minimize the damage they cause to our precious plants.
What are Sawflies?
They resemble caterpillars but are typically under one inch long.
Sawflies are a group of insects related to bees and wasps. They get their name from the shape of their egg-laying body part, which looks like a saw. Although they are non-stinging, this saw-like ovipositor resembles a stinger.
Sawfly larvae closely resemble caterpillars. However, they are smaller in most cases, rarely growing larger than one inch long at maturity. The Elm sawfly can grow up to two inches long. It is these larvae that can do a lot of damage to your plants. A group of these insects can defoliate a plant quickly.
These insects live much longer in their larval stage than adults. They can live up to one year altogether, with only one generation hatching in a year’s time. Some species overwinter in the soil as eggs or as pupae in cocoons.
Reproduction
The number of eggs a female lays depends on the species.
The adult female sawfly uses her ovipositor to cut into leaves to deposit eggs. Most sawflies are female, with only the rare male. Many species are parthenogenetic, meaning that they do not need males to reproduce. As adults, these insects live a very short time. Most live only a few days in their adult state.
The number of eggs that a female can lay depends on the species. Some will lay only one egg per leaf, while others can lay up to 100. The hatching time varies by species, as well. In general, it takes two to eight weeks for the eggs to hatch.
Why Are They Bad For Plants?
The extent of damage hinges on insect numbers and plant size.
In a word, defoliation. I have seen a group of these little guys take down a large zinnia plant overnight. One morning the leaves are perky and green, and the next, they resemble tattered brown lace. It’s not a pretty sight, and it can be very discouraging to see this happen to your garden.
Different species cause different kinds of damage. Some will chew the entire leaf down to the midrib, while others eat the tissue between the veins of a leaf. Pine sawflies prefer to eat old pine needles. Leaf miners feed on tissue between leaf surfaces.
The amount and severity of damage depends on the number of insects and the size of the plant. A large plant is likely to suffer only cosmetic damage. A large group can entirely decimate a smaller plant.
How To Identify
They are often found on the undersides of leaves they inhabit.
The adults are solitary and inconspicuous. They look like small, stingless wasps. Identifying sawfly larvae is fairly simple. They look like tiny caterpillars and often feed in large groups. When disturbed, a group of larvae may rear back, raising up the front of their bodies. This is a defense mechanism to frighten off predators.
It’s easy to locate these pests as their damage is typically obvious to the eye. They tend to remain on the underside of the leaves they feed on. Turning over a partially eaten leaf will usually reveal a group of these little larvae.
Characteristics
Sawflies resemble smooth, hairless caterpillars with six pairs of prolegs and varying colors.
Adult sawflies look like small wasps. The main difference in their appearance is their midsection. Rather than having a defined waist like a wasp, they are column-shaped, about the same width from end to end.
They have large, separated eyes and two pairs of wings. The wings are clear with veins. The hindwings are always smaller and shorter than the forewings. Their ovipositor, the egg-laying tube on their back end, is saw-shaped and resembles a stinger.
While it is uncommon to see the adults, you are very likely to spot sawfly larvae at some point, in your garden. These common pests are easy to spot as they usually appear in groups. Different species’ larvae have slightly different appearances.
The larvae resemble caterpillars, but rather than five or fewer pairs of prolegs, these insects have six pairs. These small worm-like larvae have different colorations which correspond to their species. They are typically smooth with no hair and about one inch long when they are full-grown.
Signs of Damage
Its larvae damage conifers by feeding on needle surfaces.
The damage done by sawfly larvae varies according to the species and is wide-ranging. Often, these insects will eat leaf tissue in between veins, leaving the appearance of windows. They may skeletonize entire leaves, which will turn white and eventually brown. They can also mine the leaves, causing them to roll up or curl, leaving a white pathway where they’ve been.
Some sawfly species feed on conifers. They initially feed on the surface of the needles. This will present as discolored needles, usually brown and straw-like. They can consume entire needles as they mature. On smaller plants, they can cause premature leaf drop. They will usually eat all leaves or needles on a branch before moving on.
7 Ways to Manage and Remove
While a sawfly infestation won’t usually kill a large plant, it can do a lot of harm to smaller ones. It can also leave some unsightly damage, even on larger plants and trees. Now that we know what to look for, let’s talk about the different ways of dealing with sawfly larvae. The sooner you deal with these pests, the better. As a beekeeper and avid pollinator gardener, I always advocate for non-insecticidal methods whenever possible.
Hand Removal
Regularly check under leaves and surrounding areas for larvae.
If you manage to catch the issue early, hand removal is an easy way to knock these guys out. If you walk out into the garden one morning and see a skeletal leaf with little larvae on the underside, pluck it off. Make sure to dispose of it away from your other plants.
Check under neighboring leaves, as well. If they have just about finished with the obvious ones, some of them have probably moved on. Check under the leaves in the surrounding area and pick off any larvae you see.
It’s a good idea to squish the ones you pull off. I’m not good at doing this with my hands, so stepping on them will do. Tossing them elsewhere in the garden just transfers the problem to another plant.
Make sure to keep an eye on that area of the garden in the coming days. Remove any other larvae that you notice. A few of these insects can’t do much damage. But, the fewer larvae left in the garden, the fewer adults there will be to lay more eggs.
Pruning
Remove affected foliage thoroughly and dispose of it separately to prevent spreading.
If the infestation is past the point where hand removal is convenient, you might need to reach for your pruning shears. This is probably not the most effective method if you’re dealing with smaller plants. It works best on shrubs and trees.
Sawfly larvae feed together in groups, which makes them a bit easier to deal with. If you notice large portions of affected foliage, it’s a good idea to remove them. It’s better to remove more than you need to rather than less. Make sure, again, that you dispose of these plant parts away from other plants. Destroy them whenever possible to kill the insects.
Spray with Water
Regularly employing this method can effectively minimize potential damage from pests.
It might not sound very effective, but you can eliminate many of these little pests with water. A strong stream from the hose will knock a significant number of them off of the plant. Once they are on the ground, they won’t crawl back up onto the plant.
If you do this consistently, you are likely to prevent much of the damage that these guys can do. I don’t recommend this method on smaller plants, however, as you can damage the plant in the process.
Natural Predators
Lacewings are omnivorous predators that consume other insects.
If you want to get rid of these guys and keep them gone, attract predators to the garden. Several insects love to make a meal of sawfly larvae. Ground beetles, lacewings, and ladybugs all eat these pests and won’t cause any other harm in your yard.
Adult lacewings are easy to attract to the garden. They feed on pollen and nectar, so they will be attracted to sources of these foods. Their larvae will feast on the sawfly larvae quite happily.
Adult ladybugs are omnivores, and they are attracted to pollen-rich flowers. They particularly like flowers that grow in umbels, think Queen Anne’s lace or yarrow. They also eat other insects, and their larvae are carnivorous, voracious predators.
Ground beetles, another predator of sawflies, are attracted to places where they can find shelter during the day. Mulch and leaves on the ground will provide them with a place to hide. They also like moisture.
Diatomaceous Earth
Applying diatomaceous earth under leaves effectively eliminates various infestations.
Diatomaceous earth is a powder made from the crushed skeletons of fossilized aquatic organisms. When insects crawl through it, it damages the outer layer of their bodies and will kill them quickly.
Dust the underside of leaves with diatomaceous earth to do away with just about any infestation. You can use a puffer or a turkey baster to apply a thin coating of this powder. It is safe for humans and animals, too.
However, inhaling the powder can cause respiratory issues. Be careful, and avoid inhaling the dust. The only drawback to this method is that the DE must remain dry. It doesn’t work well in humid climates. Reapply after rain.
Kaolin Clay
Consider applying this natural treatment regularly after heavy rain.
Kaolin clay is another natural way to deter pests from your plants. Mix this fine powder with water and spray the solution on your plants as a barrier. It will deter insects from eating the leaves and laying eggs.
This can be a laborious treatment, as you will need to reapply it after a heavy rain. It is natural and not harmful to humans and pollinators, though, so I recommend this over pesticides.
Horticultural Oil and Insecticidal Soap
Spray insecticidal products in the evening to minimize exposure to pollinators.
The use of horticultural oil, insecticidal soap, and neem oil is effective in combatting sawflies and their larvae. Because these can also damage your plants and harm beneficial insects, use them only as a last resort. They’re also not good for humans, so avoid contact if possible.
Spray these products in the evening to cut down on pollinator contact. A thin mist is enough. You don’t need your plants to be dripping with oil. Repeat this treatment once every week to ten days until you don’t see any sign of the insects anymore.
Contact residual insecticides are products that remain effective for an extended time. While they will eliminate your pest issues, I do not recommend them. These products are harmful to beneficial insects, including pollinators and potential sawfly predators. They are also not safe for human contact.
How to Prevent Sawfly Infestation
Treating these pests is possible, but what if we can prevent them in the first place? Well, it may not be foolproof, but there are certainly ways that we can make an effort. If we protect our plants right from the start, we can prevent sawflies or minimize the damage they can do. Some of these methods are more or less the same as the treatment options.
Encourage Natural Predators
Attract beneficial insects to your garden by planting abundant nectar.
This is always my first recommendation for keeping away garden pests. Most of the pests that eat our plants are food for the larvae of other insects. By attracting those insects to the yard, we can head off populations of pests at the chase.
Filling your yard with plenty of food for the adult insects will bring them to your garden. They reproduce where they know they can both feed themselves and their larvae. Provide these insects with lots of flowering plants that provide nectar for energy and pollen for protein. Wasps are also natural predators of sawflies, so avoid spraying wasp nests if possible.
Inspect Plants Regularly
Monitor your plants’ leaves in May and June to detect sawfly larvae early.
By watching for sawfly larvae, you can head them off at the punch, so to speak. Pay attention to the leaves of your plants around May and early June. This is when they hatch and will begin to feed. If you can identify their damage at an early stage, it will be easier to remove them physically and minimize their damage.
Treat the Soil
Minimize sawfly problems by treating soil with dinotefuron insecticide.
Adult sawflies overwinter in the soil. if you can treat the soil and head them off before they can emerge and lay eggs, you can significantly minimize the problem. This does involve drenching the soil with an insecticide, such as dinotefuron. Sadly, this can also harm overwintering pollinators like bumblebees, beetles, and moths that hibernate in the ground.
Improve Soil Health
This supports robust plant growth and resilience against insects
Improving soil health will improve the overall health of your plants. Strong plants are better able to tolerate some insect damage. By maintaining an overall healthy environment in the garden, you can support your plants. Healthy soil is a large part of encouraging a healthy biome in the garden.
Choose Native Plants
They require less maintenance and can withstand some pest damage better.
Native plants are those that grow naturally in your environment. These plants are adapted to the pests and diseases that are present, and therefore, they stand up to these better. Many are huge attractants for beneficial insects of all kinds: pollinators, predators, and more. Native plants require less care overall. Again, healthy plants are more capable of tolerating some pest damage.
Plant Trap Crops
Sawfly larvae are particularly attracted to zinnias.
Trap crops are plants that are particularly attractive to pests. By planting these nearby, you can draw many pests away from your other plants. This works with many garden insects. However, many types of sawflies are specifically attracted to one specific type of plant.
I find that the sawfly larvae in my yard go straight for the zinnias. Something about those tough leaves must appeal to them. Zinnias can bounce back easily from sawfly feeding too.
Use Weed Barrier
Use weed cloth to create a barrier against soil-dwelling insects.
Since adult sawflies live in the soil, you can create a barrier between them and your plants using weed cloth. Weed barriers help with any insects that live or reproduce in the soil. It makes it more difficult for the insects to find your plants in the first place.
Maintain Overall Plant Health
Plants with adequate hydration are more resilient against insect damage.
Maintaining overall plant health by watering and fertilizing properly is the best defense against pests. It’s difficult to entirely prevent pests without using insecticides. Since these can harm beneficial insects, they aren’t good for the garden overall.
Hydrated plants that have access to the proper nutrients will grow optimally. Healthy plants will rebound faster and suffer less overall from insect damage.
Final Thoughts
Finding your plants damaged by insect infestation can be incredibly discouraging. Knowing how to identify common garden pests is the first step in eradicating these issues. If you can identify sawfly larvae in the garden, you can treat your plants properly to minimize the damage caused by these little pests.
