Are black beetle larvae eating your lawn?

Author: Stefan Palm   Date Posted: 26 February 2020 

March is one of the two times of the year when Black Beetle larvae can cause problems and it's a prime time to spray for them so that they don't damage your lawn.

During October and 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 it's 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 doesn'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. If you can't find any evidence in this way, then your lawn problem may not be beetles. 

The best way to kill black beetle larvae is with a low toxic systemic chemical containing imidacloprid (Confidor, Complete, Tirem, Conquest and others). In this case, the aim is to kill the black beetle larvae well before they begin damaging your lawn by feeding on its roots.

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.

Imidacloprid is new aged technology designed to kill soft bodied and sap sucking insects at a very low concentration.  When it is mixed and ready to spray, it has a very low toxicity to humans and animals. However, being systemic, it is absorbed by the roots of lawn grasses and while it kills all root eating lawn grubs, it has no effect on other beneficial insects in the soil. Imidacloprid remains active in the soil for up to three months.  This is a major breakthrough as an infestation of either lawn beetles or lawn grubs (or both) can occur over an extended period.

Quick guide to lawn beetle attack:

A preventative spray with imidacloprid 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 very large numbers of witchetty grub-like larvae in garden beds adjacent to your lawn (five to six grubs per spadeful).

When to spray:

  • The best time to spray your lawn for beetles and beetle larvae is October and March.

What to use:

  • The best product on the market for home gardeners is Yates Complete. It contains 2 active ingredients - one being the imidacloprid I have already mentioned for the control of the larvae, and the other is called Cyfluthrin which will conrol the adult beetles.

Is it really lawn beetles?

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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