Are black beetle larvae eating your lawn?

Author: Stefan Palm   Date Posted: 3 November 2021 

Its not too late in the season to treat black beetle larvae in your lawn. Black Beetle larvae can cause major problems in lawns - especially if left untreated.

Around this time of year and again in March, adult beetles land on your lawn, dig a hole and lay eggs. These eggs hatch into larvae and it's these larvae that can damage your lawn as they feed on its roots. In this way, the adult black beetle does very little damage to your lawn other than to dig a hole and lay eggs. This means you should always target the larvae rather than the adult. 

How can you tell if you have beetles?

Brown patches in your lawn don't always mean beetle damage so it's good to do some investigation to determine whether you have them or not. The simplest way is to get a trowel and dig a core sample from a patchy area in your lawn - you should be able to find some larvae. The larvae resemble witchetty grubs and can range in size from a few mm long to 2cm long, depending on how old they are. Other signs to look for are birds like magpies picking away in your lawn or adult beetles coming to the surface when you flood your lawn with water. If you can't find any evidence in this way, then your lawn problem may not be beetles. 

Black beetles overwinter in lawn grass before mating and laying eggs anytime during spring. During late spring and early summer, the overwintering generation of beetles dies.  Meanwhile, the grubs or larvae that started life early in spring begin to emerge as lawn foraging beetles. At this stage, it’s possible to have both adults and larvae feeding on your lawn and if the problem is ignored, dead lawn patches quickly appear.

How do you control them?

The best way to kill black beetle larvae is with a chemical that targets the larvae. The aim is to kill the black beetle larvae well before they begin damaging your lawn by feeding on its roots.

There are a couple of chemicals that you can consider to solve the problem. Both are watered into your lawn immediately after application so they don't pose any significant risk for your pets. The best ones are Yates Complete and Yates Grub Kill and Protect. Both these products are designed to kill the larvae of black beetles in lawns and remain active in your soil for around 3-6 months.   This means that any larvae that hatch in this window will also die. 

Quick guide to lawn beetle attack:

A preventative spray with the above chemicals is warranted if;

  • You experienced serious damage (bare patches, loose turf (easy to pull)) from either lawn beetles or lawn grubs last season.
  • You observed or observe large numbers of black beetles in your lawn this spring.
  • Large numbers of birds continue to land on your lawn and appear to be feeding (on lawn grubs).
  • You find large numbers of witchetty grub-like larvae in garden beds adjacent to your lawn (five to six grubs per spadeful).

Make sure it really is lawn beetle larvae

Bare patches caused by lawn beetles and their larvae are easily confused with a range of management issues including;

  • Compacted soil
  • Non-wetting soil
  • Poor (uneven) watering
  • Annual weeds with a spreading canopy coming to the end of their growth cycle
  • Lawn diseases.

Experienced gardeners are quick to point out your best defence against black beetles is a well managed vigorous lawn. A healthy lawn can tolerate low populations of lawn beetles and their larvae.

 


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