by Wally Richards


There are three insect pests that are the main problem ones in lawns; grass grubs, porina and black beetle grubs.

The affect they have on your lawns depends on the number of the pests in a given area.

A few, will hardly be noticed, where a good number per square foot will damage the grasses and be easy to see. Damage can be seen by bare spots, brown, dead areas or discolored grasses.

Birds are a very good indicator that there are grubs in the lawn when they spend their time scratching and pecking in certain areas.

I have gardeners ringing me up about this time of the year to say they have grass grubs in their lawns or that they have dead spots.

My first question is, how do you know you have grass grubs?

They usually reply that there is dead areas or that birds are ripping certain areas apart.

Nether of these are a good indication that there are currently grass grubs actively eating roots near the surface.

If there are dead areas which have appeared in the spring or early summer then it is likely that grass grubs did cause the problem by eating the roots of the grasses in the autumn and into the winter.

The grasses would have appeared OK in the winter, even though they had little root system left, because they were not actively growing.

In the spring when they started to grow on the root system left, which was insufficient to support the grass, thus it browns off and dies.

In the meantime the grubs have burrowed deep into the soil to pupate and then emerge about October to December as beetles.

There may well be a few grass grubs in the lawn at this time and by lifting some turf you can soon find out and how many there are per square foot.

If there are a few like 1 to 5 then it’s hardly worth while bothering with a treatment, a greater number would be worthwhile to treat.

Most likely the reason the birds are working the lawn is for porina caterpillars which live in the soil. Porina come up in the early part of the evening to feed at the base of the grasses.

These are easy to control by firstly mowing the lawn to allow the spray you are going to use, to reach the base of the grasses where they feed.

Then in late afternoon mix Neem Tree Oil at the rate of 5 ml per litre of warm water and apply that to your lawn area. Using a lawn boy will do the best job to get a good coverage.

(Note the EPA has just about completed our application under the new requirements for all Neem Oils and we should be back selling later this month.)

That night when the grubs come up to feed they will get a dose of Neem and that turns off their ability to ever eat again.

If the birds eat them they will not be affected and worms in the soil will be OK too.

The time to treat for grass grubs in the lawns is in the autumn when the soil is moist and they are feeding near the surface. The other time is when they are beetles which is about now.

With porina they can be treated all year round whenever they are present.

Treatment for grass grubs and black beetle grubs can either be a strong chemical one or a safe natural one such as Wallys 3 in 1 for lawns which is a mix of Eucalyptus and Tea Tree oils.

This will not harm wild life, pets or worms, where the chemical ones will.

To treat the grass grub beetles you can use the method described in my first book, Wally’s Down to Earth Gardening Guide, extract;

Grass grub adults emerge in October, (as beetles) and are active until about mid-December, depending on weather conditions and exactly where they are in New Zealand.

The cooler the temperature, the later they emerge. The adults will start to emerge in mild conditions, when the soil temperature reaches about 10 degrees, they then mate, fly, eat and lay eggs in the short space of time between dusk and early evening.

As they tend to fly towards light, you are most likely to know they’re there when the flying beetles hit your lighted window panes.

This very attraction for the light has become one of our best weapons in controlling the pest in its adult stage.

You can set up a grass grub beetle trap by placing a trough, such as the one used when wall-papering, directly underneath a window near a grassed area.

Fill the trough with water to about two-thirds of its capacity, then place a film of kerosene on top of the water.

Put a bright light in the window, the beetles fly towards the lit window, hit the glass and fall into the trough. The kerosene acts as a trap, preventing the fallen beetles from climbing out.

You can extend this method to areas away from the house by using a glass tank, such as might be used for an aquarium.

Place the empty tank into a tray containing several inches of water (and the kerosene), and position a light inside the glass tank.

By adding a sheet of ply or something similar over the top of the tank, you will ensure that the light shines only through the sides of the tank above the waiting water and kerosene.

It is better to use a dome-shaped battery-powered light rather than an ordinary torch for this job as the bigger light makes the trap more effective.

If the tray and tank are raised off the ground and placed on something like a table, you will get an even better result.

However you set up your beetle trap, this is a very good method to dispose of the pests.

Simply get rid of all the beetles caught the next morning by flushing down the toilet or feeding to chooks.. Run this system (call it Wally’s Grass Grub Beetle Catcher, if you like) from just before dusk to about 2 or 3 hours after sunset.

We know now how to make the grubs’ preference for light work against them, but light can also work in their favour.

If you have un-curtained windows in rooms which are lit at night, you will find grass grub beetles from yours and neighboring lawns will be attracted to the area during the early hours of the evening.

Street lighting is probably the worst offender, and people with areas of lawn near street lights often find those are the parts worst-affected by grass grubs.

The beetles will eat the foliage of various plants such as roses, beans and citrus while on the wing.

Those plants that are being eaten can be sprayed with Neem Tree Oil.

If the populations of beetles are very high then in the early part of the evening take a torch and check the plants that are being eaten.

If you see lots of the brown beetles then mix up a spray of Wallys Super Pyrethrum added and go out and spray the pests.

The pyrethrum is a quick knock down and should wipe out good numbers of them.

The more beetles you can kill means less damage to your lawns next year.

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