Attack of the Root Weevils

Posted on: September 13, 2012

Or Why you should care about root weevils,  and what to do about them once you do

Close Up Picture of the Root Weevil

I have noticed that most established shade gardens have visible leaf damage  from adult root weevils (see photo showing leaf notching). It is ugly, but it doesn’t kill your plant. The serious problem is caused by their larvae who eat the roots of your plants during the late fall and winter. It is very difficult to kill the larvae because they live underground nestled into the roots of your plants to be close to their chosen food source. Think of them as tiny, tiny zombies! Rooooooooooooooootttttssssssssssssss………..

So how do you know if you have a root weevil problem? Here is what I recommend:

Root weevil damage on hydrangea in Portland landscape design

Its the damage done to the roots that we worry about. We must control the adult weevil before she lays her eggs.

Check your indicator shrubs for notching! These are Hydrangea, Red Twig Dogwood, Azalea, and Rhododendrons. Many perennials will also show the notched leaves such as Hostas and Coral Bells (Heuchera).  If you have only a few notches, you don’t have to do anything or you could treat once a year as a preventative measure.  If you have more than a few notches, we need to talk but you can also check out my blog for all the gory details of killing root weevils.  It is tricky to do.

Don’t bring them into your garden………Here is a timely tip, be very picky about buying plants on discount, or at fundraisers!  Look for notching on the leaves, and don’t buy any plant that has notching, or is near plants with notching. That means there are probably eggs in the potting soil that will hatch in your garden. You don’t want to introduce them into your garden.

Now the important part. How do you get rid of them?

The easy answer is, in the long term, the harsher one. The chemical products out there are either harmful to you or harmful to the bees which we need to keep our gardens productive and beautiful. Using chemicals to get rid of root weevils is definitively not the way to go.

I purchase living nemotodes that are specifically listed for root weevil. Properly applied, they will swim through your soil, enter the body of the root weevil larvae, and lay their eggs. The nemotode hatchlings will eat the larvae. Initially you will do this in both September /early October and the following May which are the ideal nemotode vs. larvae times!

The two  most important things ares that the soil must be warmed up and moist and you must apply the nemotodes must be applied at dusk, never in direct sunlight.   If we are having a cool May you may want to wait until June or call me and ask. In September you want to be sure your soil is well watered prior to the treatment of nemotodes, and then water well for two weeks following the treatment. This will eliminate some of the root weevil problem for 2013. You will have to repeat the biannual treatments for a few years to get the weevils properly controlled, and then continue with a once a year preventative treatment cycle (still in September OR May).

The good news is that it is really easy to do!
1) Take a 5 gallon bucket and fill it up with water.
2. Treat the water with a product called pondzyme (people use it to protect their fish from the additives in our water). I use 1 and ¼ teaspoons of Pondzyme to 5 gallons of water.
3) Add the nemotodes to the water.
4. Using a plastic pitcher I then water the nemotodes into the soil where I see leaf notching.
It is very little effort for a dramatic and healthy result.   Good gardening!

Living nemotodes for root weevil larvae can be purchased now through September at: Portland Nursery
Farmington Gardens
Cornell Farms
and other higher end garden centers.
Tranquilty Ponds has 3 locations and they sell an 8 oz bottle of Pondzyme for $26.00.  Remember you need the pondzyme to protect your nemotode warriors from chemicals in our water so don’t skip this step.  It is very concentrated so it should last you a very long time.