by Wally Richards

GRASS GRUB TIME AND A ONE WEEK SPECIAL

New Zealand has its own native root eating grub that we call grass grubs and its official name is Costelytra zealandica. Before European settlement grass grubs were contently feeding on the roots of native grasses and other nice tasting roots.

Our native Kiwi which used to be in good numbers would consume lots of grass grubs each night which kept the grub population under control.

Then the Europeans arrived. Settlers upset the apple cart by clearing native bush and planting grass to feed the stock that was introduced into NZ.

The populations of Kiwi declined and if I remember correctly when I was a boy 70 odd years ago some people thought that the Kiwi were extinct; gone the way of the Moa.

This is an excellent example of mankind changing the goal posts and changing the balance that Nature strives for.

Thousands of acres of grasses meant that grass grubs had much food and no Kiwi to eat them up so that their population then grew rapidly. The damage done to pasture and lawns became a curse for both farmer and home owner so an equaliser had to be found.

Along came DDT (Dichlorodiphenyltrichloroethane); a colorless contact insecticide, toxic to humans and animals when swallowed or absorbed through the skin, which was banned overseas (USA in 1972). In NZ; DDT was used extensively for agricultural use in the 1950s and 1960s to control grass grub and porina moth. It was also used on lawns and for market gardens.

Some 500 tons was being applied annually by 1959. By the 1970s its use was restricted and it was finally banned in 1989 — 17 years after USA banned it, the reason being that farmers had no other chemical as effective to control grass grubs. (By the way, Monsanto was one of 15 companies producing DDT.)

Interestingly other chemicals have since been used to control grass grubs in lawns and paddocks and each one has gone the same way as DDT and have been banned.

There’s also Lindane, Arsenic of Lead, Diazion and the most recent is Confidor which also has been banned or restricted because of the harm it does to bees.

There were three natural non-chemical ways of dealing to grass grubs when they are near the soil surface in autumn.

You may remember tractors with massive big stone or steel rollers on playing fields? The purpose was not so much leveling the field but to squash the grubs in the moist soil.

Farmers applied a similar method by placing a lot of cattle into a confined area so their combined weight would squash the grubs in the soil.

The third method was to flood the area to force the grubs to the surface so birds will eat them.

Birds will often tell you when there are grass grubs or porina caterpillars in your lawn as they will rip the grass out to get to the grubs.

You can find grass grubs in the lawn and gardens at any time of the year but the main lot are currently working towards the soil surface eating the roots of your grasses.

Here is their life cycle — a female grass grub beetle lays between 20 to 40 eggs in clusters about 70 to 200mm below the soil surface late spring to mid summer dependent where you are and what the season is like.

Larvae hatch in 16-21 days dependent of soil temperature. They immediately start feeding on the roots at this depth for about 3 months before moving upwards to feed in the top 60mm of soil for 5-10 weeks.

In the last stage they are feeding at 20-30mm of soil and that is the time they are most vulnerable.

They are present in this area from about April to June dependent on where they are in NZ and the soil being moist. (In a dry summer the grubs hibernate deep in the soil and it’s the autumn rains that activate them bring them near soil surface.) By cutting a square with a spade in your lawn you can lift the turf to determine their numbers.

If a few then not too much damage will occur, but if a good number in the cut square then they are going to greatly harm your grasses.

In areas where there are lights at night such as street lighting, security lighting or near windows emitting light, that is where your worst infestations will be seen as the beetles at night are attracted to the light. Also if it’s not a light situation to attract the beetles then your main problem will be the same area each year as the beetles tend to return to where they emerge from if not attracted away by light.

Once you find that you have grass grubs near the surface you can treat for them. The safe way is to sprinkle Neem Tree Powder over the lawn at 100 grams per sq metre where there are heavy infestations and at 50 grams per sq metre on lighter infestation.

The lawn should have recently been mowed before application and the soil is moist.

After spreading the Neem powder then lightly water to wash the powder down onto the soil at the base of the grass.

If you have a roller then roll the lawn to press the powder into the soil.

The next time you mow, if you have a rotary mower, then lift the cutting height up a couple of notches so you don’t suck up the powder.

If you do not use a catcher for the grass clippings then only lift one notch.

The Neem Powder will stop the grubs feeding and they will die of starvation. One of the interesting aspects of this is at the same time you are likely to control root nematodes in the grasses as well.

Most gardeners do not realise they have nematodes in their lawn and it’s only after they treat an area and notice the treated area has better looking grass than previous, that they know.

Some areas suffer from damage by the native porina moth caterpillars. The Neem Powder can also help to control this pest but the best and most simplest way is this:

Mow the lawn as normal and that evening before sunset mix Wallys Super Neem Tree Oil at 5 ml per litre of warm water and spray the lawn so that the spray will reach the base of the grasses leaves.

A lawn boy — a device that is used on lawns to apply liquids — if available is ideal for this.

This means later on when the caterpillars come up out of their tunnels to feed they will get a dose of Neem Oil and starve to death.

In areas where porina are a real problem them repeat the above every 3 months. Otherwise once or twice a year should be fine.

If you want to de-thatch the lawn then add Wallys Thatch Busta to the Neem Oil.

If you wish to use a lawn herbicide for weeds, that can be added also as all 3 products are compatible.

Do the spade test of lifting some turf and have your Neem Powder ready to use.

While you are about it, sprinkle some powder under your citrus trees as it will clean up any pests in the tree.

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