Grubs in my lawn – do I have them ? In most cases no you do not. What you think may be symptoms of grubs and beetles is usually caused by other factors, normally either a lack of water or hydrophobic soil. If you do think you have a problem with insects in your lawn it is important you go through a 3 step process first before using an insecticide. Insecticides do not just kill the target species, they also kill other types of insects that come into contact with it. The products that actually work also cost money, and we would hate you to spend money unnecessarily.
Use some Catch Cups to check water output. Put some cups in the good areas and some in the bad areas and run system. Check you have the same amount of water in each cup
If you have the same amount of water in all cups next dig down into good area and bad area and compare soil moisture. If the bad area is drier apply commercial grade wetting agent to this area.
Lastly flood the good area next to the bad for about 1 sqm with a wetting agent. See what floats to the surface. If you get a couple of beetles / grubs this is fine. 15 to 25 and you have a problem
So you have determined that grubs and or beetles are the problem. Generally adult moths and beetles are attracted to healthy lush lawns. They will lay their young in a lawn that will give their baby grubs the best start in life. After the baby grubs have decimated an area the adults will just move onto the closest healthy bit of lawn and start again.
Often when householders notice they have a problem the moths and beetles will have already left this area and being happily munching down on a new patch of green. This is why when you look for the sign of grub life in the decimated area there is none, they have already moved on!
This is why when checking if your beautiful lawn has any squatters, you dig down into the healthy area just bordering the already eaten part and have a look there for the signs of grub life. Different species of grubs have different habits, including whether they eat the roots or leaves of your grass and where in the profile of your lawn they live. Some prefer to live in the soil, while others like the thatch layer of your turf so make sure you dig to about the depth 20cm and pull the turf apart and have a good look. As above you also soak the lawn area with a wetting agent. The wetting agent will ensure the water penetrates into the soil. It is a waste of time to apply the wetting agent to the brown dead area as it is likely the grubs will have moved on. The wetting agent should be applied to the edges of the eaten and healthy area and see if any grubs come up. You can also place a damp hessian bag down overnight and have a look in the morning if any are present.
Wasps hanging around your lawn are also a good indicator of having a lawn grub problem. The parasitic wasps lay their eggs in host larvae, commonly lawn grubs. This is good for the lawn as it kills the host grub.
Grubs laid by moths can be more difficult as the adult moth is harder to kill.
The beetle variety can be easier to break the life cycle because you can kill the adult beetle,
Some species of grubs are also much more likely to do damage to your turf then others. This will depend on whether the species you have in your lawn occurs in plague proportions and literally eats the lawn, or whether it is the humble lawn beetle laying a few grubs in a healthy lawn and not causing any damage overall. A few lawn beetle grubs in a healthy lawn are generally no problem, live and let live.
A few lawn beetles in an unhealthy lawn with a weak root structure can however cause a fair bit of destruction.
If your lawn is looking decidedly sick (and the leaf looks chewed on close inspection) there is a good chance you have one of the lawn grubs that does occur in plague proportions. These species are normally laid by moths and include web sodworm and army grub.
Army worm infestation in our front lawn Feb 2018
The green muck is their poo. Our grass being recycled!!
They can constantly eat more then their size
Sod webworms prefer fresh new grass (freshly laid), however they will choose an older lawn if it is healthy. This is because new lawn stores more nutrients in the leaf until the roots are into the ground and sod webworms eat the leaves of your lawn.
These grubs are tan or grey in colour (grey as they get older). In autumn, winter these grubs are in their juvenile stage and live in their silky tunnels in the thatch and soil. If you look at root level, you can see small white tubes made of silk. You may also see small green faecal pellets. In spring they start to get active and they mature into moths throughout summer. During the afternoon the adults scatter their eggs over the grass by flying in a zigzag pattern. During the heat of the day they hide in plants and in the turf and in the cool of the evening they come out to feed on the leaf and stem of your grass, although it is the larvae that do more damage than the moths. The webworm eats the grass down to nothing.
It is best to apply your pesticide in the late afternoon or early evening. Do not mow or water for 3 days after application if using a liquid. If you are using granules you will need to water it in to get it down to the roots and soil. You will need to re apply to break the cycle after about 10 – 14 days and probably every couple of months after that through to winter as the adult moths will keep coming back to your lawn if they like it.
Armyworm are a problem in your lawn areas normally between autumn and winter. The juvenile larvae are initially cream and attain a greenish colour after feeding. Adult caterpillars are brownish with characteristic stripes and black triangular marks along the back and are about 45mm long. When disturbed they roll up into a ball like a slater. Adult armyworm moths are greyish brown with a small wing span.
Female armyworms mate the first night after emergence and two days later they lay their eggs between dark and midnight.
Larvae often feed on the leaf blades, leaving the middle of the leaf, giving it a tattered appearance. They feed only on the soft parts above ground leaving the roots undamaged.
As the armyworm feeds at night it is best to apply your pesticide in the late afternoon or evening. As the roots are intact the plant is still viable so fertilising with a high nitrogen and iron fertiliser like our Knights Special Mix will promote new leaf growth. The high iron content of our Knights Special Winter Mix will also help if your lawn has gone dormant in winter.
Lawn Beetle grubs does not always appear in plague proportions, it is not uncommon to have a few on your lawn causing no problems. They do however eat the roots of your turf so the damage can be more lasting if you do have a lot of them.
If your lawn has a weak root structure, they can be a problem. If you only have a couple it is more beneficial to get your lawn healthier then to spend money on grub killer. You might kill the few lawn beetle grubs you have but this will not strengthen your grass. In this case you are treating a symptom, not the cause. See our fact sheet on 3 Easy steps to have a healthy lawn for help with this.
Also remember that sometimes people give the lawn a good drink when they apply the pesticide. This drink could be enough to colour your lawn back up for a couple of days and home owners make the mistake of thinking the insecticide has made the difference!
Pesticide should be applied 14 days apart to break the life cycle of the beetle. Sometimes this may take up to 3 applications depending on the product used. As always a fertiliser with a good NPK ratio for lawns should be applied. Make sure you use a fertiliser with phosphorous to help the root structure.