More Sawfly Questions Than Ever!

Sawfly damage on bur oak leaf. Larvae have fed on the opposite side of these leaves.

There were several questions daily. On Facebook. In my newspaper columns. On my radio program. In my emails from friends. After church talking with friends.

Sawflies were obviously driving folks crazy. Oak leaves were being eaten away and folks were fearing the worst. But let me give you a few basic facts.

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What you should know about sawflies…
There are many species. Each carries the name of its host tree in its own name. So you have “oak sawflies,” “elm sawflies,” etc.

Shumard red oak is a frequent target of oak sawflies. So are live oaks, bur oaks and chinquapin oaks.

The adult is a short-lived and almost unnoticeable wasp-like insect that lays her eggs on the leaf surface after using a part of her body to cut a slit into the leaf tissue, hence the name “saw” fly.

I downloaded this great photo from a university website a few months ago but now can’t find the source in order to give credit. This is what sawfly larvae look like as they feed.

The small larvae are gelatinous and harmless looking at first, but as they go through successive instars (phases), they get larger and their damage becomes more noticeable.

You can see the parchment-like look of the leaves and the network of veins.

The larvae feed on the bottoms of the leaves, skeletonizing them and leaving just a network of veins.

There is usually only one generation per year. The larvae fall to the ground with the dead leaves at the end of the season and emerge the next spring to start the cycle over again.

By the time the damage has become evident it’s too late for much control. However, if you catch them early enough general garden insecticides (not including B.t.) will usually stop them.

The good news is that their damage is only temporary. Affected branches will leaf out again the following spring.

I posted a good reference sheet from Ohio State on this topic on Facebook last Sunday.

Here is a very thorough explanation of sawflies from the University of Wisconsin Master Gardeners program.

Posted by Neil Sperry
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