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Wally Richards
Wally Richardshttp://www.gardenews.co.nz
Wally Richards has been a gardening columnist for over 30 years. Check his websites - for gardening news and tips visit www.gardenews.co.nz. For mail order products visit www.0800466464.co.nz. Wally also has a gardening problem help line on 0800 466 464.

Gardening with Wally Richards: Grass grubs – now is the time

Grass grubs news

I am often asked is it the best time to do certain things in the garden and more often than not when asked it is not the best time.

Gardeners sometimes miss the boat and only later when the damage is done or the plants are out of season, that they look for the solution.

When I had a garden centre I would have new-by gardeners coming in during the spring looking for daffodil bulbs/plants, cause they saw them flowering in peoples gardens.

This also applied to tulips and other spring flowering bulbs. Now is the time to buy your spring bulbs and plant them.

Lawn problems caused by grass grubs are noticed in the spring when patches of lawn die.

Treatment then is a total waste of time and money because the grubs are in most cases deep below the surface in cocoons waiting for the right conditions to emerge as beetles.

Any treatment applied in the spring may catch a small amount of grubs and not worth the expense.

What has happened is way back in October through to about December (maybe January) the grass grub beetles were on the wing chewing up the foliage of your plants in the evening and laying up to 300 eggs per female back into your lawn or gardens.

As these eggs are laid deep in the soil and when the grubs emerge they start eating the roots of the grasses (or some other plants) this is way down about 200 mm under the soil. The grubs are small and the damage done is not great.

The grubs grow and keep working their way upwards as the roots are eaten out at the lower depths.

If the soil becomes dry during a summer drought, the grubs go into a semi dormant state waiting for the moisture to return.

This normally happens with the autumn rains and the grubs wake up and start feeding again getting closer and closer to the soil surface.

Now if we cut a square in the lawn with a spade about 50mm deep we are likely to find a number of the white grubs in the area we have lifted.

These grubs curl up when disturbed. Any greasy looking caterpillars found are the porina.

If you lift turf in different areas of the lawn you can see where the worst problems are in other words where the most grass grubs are.

These are likely to be found in areas where there has been past problems or in areas near where lights shine at night, because the beetles are attracted to lights in the early evening when they are in flight.

You may find that in some areas in the turf you lift there are either no grubs or only say under 6 per square foot. In other areas you may find lots of grubs in a square foot. Its those areas you should concentrate your efforts as that is where damage will occur and be noticed.

There are currently two non chemical treatments available.

The liquid one is Wallys 3 in 1 for Lawns.

The product consists of Eucalyptus oil and Tea Tree oil along with natural plant foods in the form of manures and seaweed/fish extracts.

Available in 1 litres containers which cover 50 square metres of lawn or gardens.

Follow the instructions for mixing with water and it is best applied to the lawn in a device called a Lawnboy.

After application the lawn is further lightly watered with the hose or a sprinkler to wash the oils off the grass and down into the top 6 to 10cm of the lawn. It is there that it does its job.

Often lawns are the home of garden slugs which emerge out of the soil and thatch to invade our gardens during moist times. The product knocks them out also.

Worms will happily live underneath the oil layer in the top soil without any known adverse effects.

Worms that are near the surface when applied may not fair so well.

This means it is best to apply the product when the soil is moist but not after a good amount of rain which tends to bring worms to the surface.

I have found that these oils will control other soil insects such as eel worm, centipedes, root mealy bugs, porina etc.

Even the likes of earwigs and slaters can be given the old hurry on if they are causing problems.

The manufacture informed me that the oils act as an irritant to the pests and they succumb as a result.

Imaginative gardeners may find this product an interesting tool in assisting in the control of some pests such as wire worm in the soil by treating the area a few weeks before planting (say) their new seasons potatoes.

The product is only recommended for lawn use and ideally should only be used for the control of pests in the lawn areas.

Used for any other purpose is not recommended but being two natural oils I cannot see any health concerns as you are not likely to spray over any food crops and eat them without first washing as normal.

Being a oil based product, it can of course burn foliage and grass if applied in sunlight.

For lawn applications it is recommended to use early in the morning or late afternoon and washing in with the hose, the oils off the foliage and into the soil.

Safe for your children and pets unlike the previous mention products.

The other natural product is Wallys Neem Tree Powder.

I suggest powder as it is less easy picked up when mowing the lawn.

Once again after you have done your spade tests on where the most grass grubs are then you really only need to treat those areas.

Spread the powder at 50 to 100 grams per square metre onto a recently mowed lawn and when the soil is moist.

Lightly water to settle the powder off the grasses and get it down to the soil surface.

If you have a roller or can hire one then roll the areas treated to press the powder into the soil.

It will breakdown and release the Neem properties which will be taken up by the roots of the grasses.

Thus when Mr Grass Grub takes a bite of the root he gets some Neem into his gut and it turns off his ability to eat any more. Thus he starves to death.

Most effective and safe for children, pets and soil life.

Now is the time to treat Grass Grubs.

If your lawn problem just involves porina caterpillars then the most effective and less expensive treatment is applications of Wallys Super Neem Tree Oil applied late in the day on a freshly mowed lawn.

You should use a lawnboy to drench the grasses at the rate of 5 mls of Wallys Super Neem Oil per Litre of water or a boom spray nozzle on your back pack sprayer.

You are looking to get a coating of the Neem Oil to the base of the gasses where the porina is going to feed that night. Once they get some Neem in their gut they will stop eating and starve to death.

Treatment for porina can be done anytime of the year as they are a all year round pest.

Image credit: Tobi

Products mentioned are from Wallys Range of products and can be found in some garden shops or by Mail Order on www.0800466464.co.nz

Problems ring me at: Phone 0800 466464
Garden Pages and News at www.gardenews.co.nz
Shar Pei pages at www.sharpei.co.nz
Mail Order products at www.0800466464.co.nz

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