Root Weevil Damage in Portland Gardens
Why you should care about root weevils, and what to do about them once you do.
Many Portland established shade gardens have leaf damage (notching) from adult root weevils.
A lot of leaf notching can spoil the looks of the plant just when you wanted to enjoy its beauty. 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! Roooooooooooooooottttts
So how do you know if you have a root weevil problem?
This is ugly but it’s the damage done to the roots of your plant we need to control. We must control the adult weevil before she lays her eggs. (hydrangea with lots of leaf notching)
Check your indicator plants for notching!
My indicator plants are Hydrangea, Red Twig Dogwood, Azalea, and Rhododendrons as well as many shade to part shade perennials and vines. Hosta and Coral Bells (Heuchera) and Heucherella as well as clematis vine leaves are on their favorites’ list. If you have only a few notches here and there in your garden, I recommend treating once a year in September as a preventative measure. If you have more than a few notches, read on for all the gory details of killing root weevils. It is straightforward once you know what to do.
Preventative Steps
Don’t bring them into your garden………Here is a timely tip, be very picky about buying plants at any time of the year but especially on discount, or at fundraisers! Look for notching on the leaves, and don’t buy any plant that has even one single leaf notch, or is near plants with notching. Root weevil can walk over to the plants near by and lay eggs so even if there is no notching on a particular plant if there are plants near by with damage…odds are good there are eggs near the plants roots and in the soil. You don’t want to introduce them into your garden. (I’m not saying they came from your freshly purchased potting soil….that is a non starter…)
Treating Root Weevil
Now the important part. How do you get rid of them?
Handpicking the adults during late April, May and June is helpful but isn’t as effective as preventing the eggs from hatching using nemotodes. Tellima grandiflora is a native shade plant I use in designs.
Controlling the adult root weevil without using chemicals:
I suggest a combination of treatments. Hand picking is the easiest to do and will have an immediate effect if you pick enough of them, but they can be very hard to spot. This dull colored beetle is only 1/4″ and hides effectively in the top of the soil or inside a leaf crevice. Checking your plants on overcast days or evenings with a flashlight to find them. The best time for handpicking is after you see fresh leaf notches in your indicator plants. May and June are top choice for picking the adults out of mulch around the plants, or in leaf crevices or in the act of munching the edge of a leaf.
Sticky foot or tangle foot. Spread this gooey white paste on the lowest stems of the indicator plants. This will trap some of the
Here is a darker colored root weevil, many are a more dusty gray but all are quite small, smaller than a dime.
adult root weevils as well as other insects unfortunately. Its chemical free but if you have a pet that will eat anything, I would hesitate and do more research before using.
The chemical products used to control the adult root weevil are harmful to you, your pets and the bees which we need in order to have food. Please do not use chemicals to get rid of root weevils.
The best way to minimize or eliminate adult root weevil is by using nemotodes properly. I purchase living nematodes that are specifically listed for root weevil. Properly applied, they will swim through your soil, enter the body of the root weevil eggs and lay their eggs. The nematode hatchlings will eat the larvae from the inside out.
Timing Matters
Properly means the right timing. Initially you will do this in both early September/early October and the following May which are the ideal nematode vs. larvae times! If you have an infestation with lots of leaf damage I would add a treatment in June and treat 4 times a year for 2 years. You will be able to see the progress and can do fewer treatments.
The 3 most important tips:
- Before treating, the soil must be warmed up and moist.
- Apply the nematodes at dusk, never in direct sunlight.
- Get the timing right-treat in May or early June. Treat again in September. Treat and water well for two weeks following the treatment. This does not kill the adults who will continue to feed on your plants but it will eliminate the eggs. This will help the following year. 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 (in September).
Add Pond Zyme You’ll get better results if you use Pond Zyme in the water before you add the nematodes. It protects your nematodes from the chemicals in our Portland water.
The good news is that it is really easy to do…ok wait it’s tedious… but your shade garden can look so bad if root weevils become numerous.
1) Take a 5 gallon plastic bucket and fill it up with water. (no metal buckets with Pond Zyme).
2) Treat the water with a product called Pond Zyme (people use it to protect their fish from the additives in our water). I use 1 and ¼ teaspoons of Pond Zyme to 5 gallons of water.
3) Add the nematodes to the water.
4) Using a plastic pitcher, not metal, I then water the nematodes into the soil where I see leaf notching.
It is very little effort for a dramatic and healthy result. Good gardening!
You can also use a hose end sprayer if you are not using the Pond Zyme.
Nemotodes Resources
March Biological is mail order. I like Brad the BugMan (March Biological) so order from him on line.
Living nematodes for root weevil larvae can often be purchased May through September at retail garden stores, not big box, Portland Nursery for instance.
Remember you need the pond zyme to protect your nematode warriors from chemicals in our water so don’t skip this step for best results. It is very concentrated so it should last you a very long time. Other people claim to have good results without the Pond Zyme. My experience with my clients is that Pond Zyme makes a big difference in the efficiency of your treatment. We used to have local stores that handle pond care and they will have Pond Zyme. My link is to a company that I know Nothing about it. Hughes Water Gardens is the only retail pond store left that I know about.
Contact me if you want a landscape designer who knows what it takes to have an attractive and healthy landscape. I know what plants are a hole you pour your time into and what plants give great results in your landscape and in our environment. And when trouble strikes my clients landscapes, I can advise what needs to be done. [email protected] or use my contact form.
