In south east Queensland lawn grubs have become a real concern. They are most active in the warmer months of October – March so now is a great time to learn what to look for and how to get rid of lawn grubs.
Thinking that your lawn is too healthy to have lawn grubs? Think again. Lawn grubs love a thriving, healthy green lawn. Firstly – what is a lawn grub? In Queensland there are a few different types of pests that we all commonly refer to as ‘lawn grub’, mainly the Army Worm and the White Curl Grub.
White Curl Grub
This is actually scarab beetle larvae which is the juvenile stage of lawn beetle. It is often, incorrectly, known as a ‘lawn grub’ or ‘witchety grub’. White curl grubs are a serious lawn pest and the signs of infestation are easily confused with other pests, diseases and disorders in turf. The end result of a white curl grub infestation is basically, yellowing to browning and ultimate death of the lawn. White curl grub will eat away at the root system of the turf which, in turn, causes death, with a serious infestation, you are often able to roll your turf up as the root system is completely destroyed! Every lawn in Queensland at this precise time will have some white curl grub present and an infestation is generally regarded as a problem when there are 25 or more grubs existing per square metre. If less, a normal and healthy lawn with seasonal growth will sustain any damage caused. However, other external influences may likely exacerbate the problem, such as heat or drought conditions. If you have concerns, the best way to check for lawn grub is to grab a hessian bag or piece of old carpet and lay it on the grass in the late afternoon. Wet the bag or carpet thoroughly and leave overnight. The following morning the lawn grub will have been drawn to the surface, and an assessment can be made.
The next lawn grub critter is known as Army Worm. The adult lawn armyworm takes the form of a greyish-brown moth with a wing span of 35 to 40 mm. Damage from these differ slightly from the white curl grub, as they work similar to that of other caterpillars, eating away at the leaves of the turf and damage is often seen as a clear line of dying grass marching across your yard. Often starting closest to the house near external light sources, which attract the adult moth. Determining if you have an Army Worm problem is the same process as above with the white curl grubs. However, be aware that if you have had some reasonable damage occur you will need to be smart with your test placement. Obviously, the grubs will have already moved on from the ‘dead patch’ and will now be working on the adjacent green lawn.
Lawn Grub Prevention
The lawn grub have impeccable taste and won’t settle for a lawn already struggling – the house with the nicest lawn is generally the one who gets hit the hardest! Prevention is the key to avoid lawn grub but most commercially available pesticides are designed to treat an existing problem of lawn grub, rather than prevent it from occurring. Some of the granular mixes can be present for a short time after application and so will inadvertently prevent lawn grubs developing. The place to start in terms of prevention is ensuring your home, shed, fences and eaves are all free of moth nests. These range in appearance but most look like little cotton-like cocoons. The best way to get rid of them is with a hose and a broom. It’s not a guarantee but at least you are limiting the amount of moth activity around your property and hopefully the number that will have the opportunity to turn into lawn grubs.
Lawn Grub Treatment
The most effective treatment for an infestation of lawn grub is a chemical approach. Chlorpyrifos seems to be one of the most effective treatments and is available in both a liquid concentrate for spraying and a granular form to be dispersed over the lawn and watered in. Exercise extreme caution with these forms as they can also be lethal for animals and children. Treat your lawn in the late afternoon when birds are less active. The birds are attracted the wriggly (and dying) grubs which come to the surface of the lawn after treatment. Always read the label and apply at the recommending rates. It is important when treating an infestation to break the lifecycle which is why treatment is recommended over a 2 week period – on days 1, 7 and 11 to break the cycle of cocoon – moth – egg – grub – cocoon. The active ingredient of Chlorpyrifos is often also present in many commercially used products for treating ant and other insects. So while you are able to get rid of lawn grubs, you should also see reduced numbers of ants, lawn beetles, African Black Beetles, cockroaches and spiders.
The Organic approach to getting rid of lawn grubs
A natural, organic approach generally relies upon early mornings, a good lawn care regime and carnivorous birds.
Getting up early
A low-tech way to get rid of lawn grubs involves an extension of the hessian test. Lay wet hessian upon the lawn overnight. The lawn grubs will attach themselves to the hessian and you can then pick up and dispose of them early the next morning.
Mow lawns higher since both beetles and moths love laying their eggs as close to the soil as possible. Having a long and healthy grass blade is the best defence against lawn grub infestations.
Lawn grubs thrive in a moist environment and our lawns shouldn’t be consistently moist anyway. Only water your lawn as and when necessary and only when the grass is showing signs of heat stress and deterioration – curling and yellowing blades. Water less frequently but more deeply to encourage deep, strong roots, drought tolerance and to deter lawn grubs.
Regular lawn aeration using the lawn coring or garden fork methods will greatly aid in creating a healthy strong lawn and aeration will encourage deeper, stronger roots which are far more resilient to lawn grub attack. Aeration is best done using lawn coring which will also help to control thatch build-up. Alternatively, a garden fork can be dug into the soil to help aerate the soil.
Many wasps lay their eggs inside beetle larvae, which in turn kills the beetle. While having a few wasps in the yard is not for everyone, wasps can be a good friend to your lawn.
Birds love to eat many different lawn and garden pests, including all lawn grubs, as well as caterpillars and many other insects. Encourage birds into your yard to naturally control many different lawn pests by planting trees and bushes which are most native to your region, install a bird bath and keep it filled with clean water. There are a number of methods to encourage the birds to get rid of the lawn grubs for you, including flooding with water, and also soapy water, which will encourage the lawn grub to the surface, where they will hopefully be picked off by such birds. As you can imagine, this method can yield some rather scattered results!
Make your lawn less interesting to grubs
Lawn grubs are actually quite discerning and prefer some grass types to others. Couch and Kikuyu lawns are more prone to grub infestation than Buffalo grasses, like DNA Certified Sir Walter grass. If you’re investing in new turf, then this is something to consider. Be careful when you fertilise as lawn grubs will see this as an invitation to move in and make themselves at home. This is especially important around January and February while the climate is typically very warm and wet. Lawns that require little in the way of fertiliser – such Sir Walter Buffalo grass comes to mind, which will be much less appealing to grubs.