African black beetle in lawns

With all the rain we’ve had over the past week, you may have noticed a few black beetles hanging around on the surface of your lawn. It’s not uncommon to see beetles after rain, and can indicate that you may have a black beetle problem under your lawn.

There is no doubt that African black beetles (Heteronychus arator) love the taste of lawns and need to be dealt with when their numbers get too high. While most people will have heard of black beetles, most won’t know a lot about them, how they breed, their lifecycle etc, and I think that it’s important to have some understanding, especially when it comes to controlling them. The risk is that at the first sight of a beetle, or a brown patch in your lawn, you’ll rush out and buy a beetle chemical and apply it to your lawn. While this can be an appropriate response, there are many instances where it isn’t, and doing so doesn’t help. Further to that, the bio-diversity in the soil under your garden will thank you for taking a cautious approach to applying chemicals and reserving such actions for times only when necessary.

What is a Black Beetle

I’d say that every gardener has seen a black beetle or two in their lifetime but to save any confusion, below is a photo of what an adult beetle looks like. There are many different types of beetles that you may see around the garden – this one is shiny black in colour and about 12-14mm long.  

While adult black beetles can cause a significant amount of damage to various types of crops, by themselves, they are not much of a threat to the common types of lawn in South Australia, such as couch, kikuyu and buffalo.   

It’s their larvae that cause damage to lawns, feeding on the root system as they develop from egg to larvae to adult. Newly hatched larvae are around 5mm long and grow to around 25-30mm long before they mature into adults. They kind of look like a witchetty grub.  

Lifecycle:

Understanding their lifecycle is key to controlling the problem. An adult black beetle is a flying insect and lives for around ten months. Come early Spring; they’ll fly onto a lawn, dig in and lay some eggs. Those eggs take approximately four weeks to hatch into what’s called the first instar stage, and this is when the larvae are at their most vulnerable. The larvae will progress through their various stages (1st instar, 2nd instar, 3rd instar) over the course of four months until they emerge as adults between December and February. The more mature a larvae becomes, the more resistant they become to chemical control. This means that the best time of year to control them is October and November.

Damage caused to lawns:

As I mentioned earlier, adult beetles are of little concern to a lawn other than they lay eggs, leading to the real issue, which of course, is their larvae. Over the four months that the larvae spend maturing, they feed on the root system of your lawn. One or two larvae in your lawn won’t represent a big problem. In fact, healthy, warm-season lawns such as couch, kikuyu, and buffalo can tolerate a low-level population without you even noticing that they are there. It’s when they attack in high numbers that you’ll start noticing dead and dying patches in your lawn. As the larvae eat the lawn roots, the lawn becomes less able to extract water and nutrient from the soil, leading to it drying out.   

While dead and dying patches can be a sign of beetle larvae activity, they can also be a sign of virtually every other problem that can affect a lawn. When you see dead and dying patches in your lawn from the months of September through to March, I’d get out with a trowel in your hand and dig some small core samples in and around the dead and dying patches. Look for the presence of larvae and have a look at the root zone of the lawn while you’re there. If it is beetle larvae damage, you’d expect to find some beetle larvae, and in extreme situations, the lawn may simply lift off the soil because there are no roots left. If you can’t find any larvae and the root zone looks good, it may not be beetle larvae causing the damage. While this level of investigation can seem time-consuming, it’s an important step because, in doing so, you’ll get a better idea of the issues affecting your lawn. Suppose the problem isn’t beetles, and you simply apply a beetle killer without doing any checking. In that case, you won’t have solved the problem, and you will have needlessly applied chemicals to your lawn, costing both you and the environment something significant.

Dead and dying patches can be a symptom of disease, non-wetting soil, maintenance issues, watering issues, shade, turf mites, and the list goes on, so it’s important to correctly identify the issue first before you seek to address it. I have to say that after consulting on thousands of lawn problems over the years, statistically speaking, it’s far more likely to be one of the above problems than it is to be beetle. I’m not saying beetle problems don’t occur; I’m simply saying that they are less often the cause of dead and dying patches than you might think.  

Tips for Black Beetle Treatment

Once you have identified that you have a beetle problem, the best solution is to apply an insecticide to control them.

Look for chemicals that contain chlorantraniliprole (acelepryn). These chemicals will last in the soil for up to six months and specifically target the larvae. Any new larvae that hatch inside that window will die too. I can recommend products such as Yates grub kill and protect and Acelepryn GR, as both these products offer long-term control. They also control other lawn beetle pests, including argentine stem weevil larvae, billbug larvae; and lawn caterpillar pests, including armyworm, sod webworm, and black cutworm. 

Applying a beetle control product containing Acelepryn in Spring will, without a doubt, prevent infestations from occurring. As this will last in the soil for up to 6 months, you won't need to re-apply for 12 months.  I mentioned this earlier, and it’s worth repeating that the timing of the application is really important. Spring is the prime time as this is when you'll have the most larvae activity, and this is when they are at their most vulnerable.  If you leave your application till Summer or even Autumn, your results won't be as good - I’ve seen advanced larvae withstand some pretty hefty chemical applications!  

Regular monitoring of your lawn will ensure that a major infestation doesn’t appear overnight.  Well-cared-for lawns are more likely to resist and recover from beetle larvae attacks than neglected ones, so proper lawn maintenance is always a great first defence.

As always, if you have a problem that you can't seem to solve, give us a call on 8298 0555 or email me at stefan@paulmunnsinstantlawn.com.au