In previous blogs I have looked at what is a chafer grub and the life cycle of the chafer beetle. In this post I’ll be looking at how to identify chafer grubs, and what you can do to control them in your lawn.
Chafer grub damage to look for …
Before considering a remedial treatment, you need to identify the pest or disease. There is no point in applying expensive treatments which are wrong. At best you’ll waste your time and money, at worst you could actually cause harm to your grass.
It can be tricky to identify a chafer infestation, as they live underground. But there are things to look out for:
- Is it the time of year for chafer grubs? The grubs are most active during autumn and spring. If the damage occurs outside of these seasons, there is another cause.
- Does the grass look stressed or dry, or has small circular dead patches for no clear reason? If you have good growing conditions and the grass has died, this can a sign that they have had their roots eaten. Time to investigate.
- Grab the grass by the handful and try to lift it away. A healthy grass will have a strong roots system and be very strong. A pest-infected lawn will come away like pulling up a carpet. The grass may fall apart. If you are lucky you may find a grub near the surface!
- Are other animals are taking an interest in your lawn? Is the grass pulled up or have holes appeared? Is there a lot of activity by large birds in one area (magpies, rooks and crows)? Does an animal dig in the lawn overnight? If so, you may have a grub infection. For the UK this will either be leatherjackets or chafer grubs.
If you find any of these symptoms, but no grubs on the surface then it’s time to dig a little deeper.
Dig for chafers
Find a sturdy garden knife, around six inches long. Cut a wedge out or cone or soil out of the turf around the damaged area. Have a dig in the soil and roots and try to find the white C-shaped chafer grubs. If you find none, have a look in a few other places around the lawn. If you find no grubs, look for another cause and watch the area. They may have already flown or been eaten.
Chafer grub damage can sometimes be very dramatic, as I found at this customers garden in December 2017.
Current chafer grub chemical controls
Before I move on to current chafer controls, I have to clarify the current situation on chemicals.
ALL HOME AND PROFESSIONAL INSECTICIDES TO CONTROL CHAFERS WERE REMOVED FROM THE UK MARKET IN 2015.
Imidacloprid (manufactured by Bayer) was the main insecticide used for Chafer grub control. The Health and Safety Executive, Chemical Regulations Division withdrew this from sale in the UK in 2015 (and professional use by October 2016). This means that it is currently ILLEGAL to use any insecticide to control chafer grubs on turf. This includes any which you may still have left over or found in the back of your garage.
You should take any old chemicals to your local authority chemical disposal site. DO NOT POUR THEM DOWN THE DRAIN or dispose of them IN YOUR GARDEN!
The removal of these insecticides has meant that control of this already difficult pest has become much more difficult.
Some older sources may refer to rolling your turf to compress the soil. The theory was that it restricted the grub movement. This outdated advice is not recommended.
Nematode control for chafer grubs
The current, most effective, method to control chafer grubs is nematode worms. This is a biological pest control. This involves introducing a microscopic, parasitic worm to the chafer environment. The worm enters the chafer and produces a bacteria which multiplies and kills it.
The nematode is Heterorhabditis megidis and is safe for use in the garden as it only targets chafers. It does not target any other creatures.
You can buy nematodes online during the season of application. They are a live product, so you must store it in the fridge until use.
It is then mixed with water (and a wetting agent) and applied to the soil when it is moist and warm. It is also advised to either water the nematodes in, or apply when rain is forecast. The nematodes need to actually get down to the chafer to be effective.
After 3 days the chafer will stop eating and be dead in 2 weeks.
This method is expensive. (currently £27.99 per 100sqm) so if you have a large lawn this may not be viable. Results can also be sporadic, due to the fact that you are working with nature. It sometimes works, other times not so much.
Nematodes have very specific application requirements, storage and aftercare. I am unable to offer nematode control as part of my professional lawn care services. I am happy to provide advice for homeowners in nematode application.
Other chafer controls
One method which you can try is to try to tempt the chafers to the surface and to let the birds eat them.
Give the affected area a good watering and lay a piece of carbon black-out or weed-suppressing membrane over the area. Leave this for a few days and the grubs should be on the surface of the grass. Then leave them for the birds!
Again, if you have a very large area to treat, this may not be possible. However, it is a cheap and easy method of natural chafer control.