Expert: Jim Gibbs - 6/2/2004

Question
I seem to be losing some of my grass to grubs.
What's the best way to control and what products
and when is the best time to apply.Thanks.

Answer
Hi F.bacchus,

ABOUT GRUB-WORMS in LAWNS:

"Grubs" or "grub-worms"  are the larval stage of development of several routinely encountered common summer beetles.

These are common insect pests of all turf-grass lawns and can also reside in the soil near the roots of  many species of other types of plants to do their root-feeding damage. The affected grass and plants die a slow death weakened by having their roots destroyed with the grub root-browsing.  If your property is near "wild" fields or similar un-tended areas, grubs will generally be an on-going battle. With lots of grubs in the soil, other pest which feed on the grubs (such as mice, moles, voles, gophers, etc.) may also become a problem.

 There are more than 40 species of insects which have a "grub-worm" larval stage in the top-soil; fortunately almost all can be controlled and the damage prevented if the home-owner is observant and informed.

In the intermediate horticultural hardiness zones (5-8), the insect eggs get deposited in the top-soil in mid-late summer and they can over-winter as the eggs hatch to produce grubs in accordance to the variance of the temperature of the root-zone.  Where there are warm areas in the winter lawn such as near reflective brick-walls, the grub-worms can get an early start in the spring.  In locales with more harsh winters and colder soils, the grub stage is later in the spring.  In warmer climates, the grub problems may be continual.

Grubs can vary in size from 3/4 to 1-1/2 inches.
Some grub larval forms are white in color while others are brownish or grey.  The term 'white-grubs' usually refers to the common larvae of the 'May-Bugs' or June-bugs'. Technical identification of a larval beetle damaging the lawn is usually not necessary.

In the USA, there are several different types of Beetle produced "grubs" that are the main problems for lawns.  The non-scientific or 'common name' for the various beetle species that cause grub-worms infestations in lawns is not a dependable identification and one name may refer to several distinct species;... these common names include:

May beetle,
or 'June-Bug',
Southern Masked chafer  and
Billbug grubs.

The southern masked chafer is the most common and is best controlled with a preventative (see list below) insecticide application in late July or early August.


INSECTICIDE CHEMICAL CONTROLS:

In the summer months, you should spray-kill or otherwise work to eliminate the adult insect-beetle as soon as you see them. Similarly, when working the soil, if and when you find the larval grubs in the root-zone, you should consider applying a grubicide to the top-soil.

One egg-laying female beetle can produce many hundreds of grubs for the next season's population, so killing the adult beetles is an efficient way to become grub-free.  Some of these beetles can fly about and are active after dark and are easily attracted to a porch or night lights and electronic 'Bug-Zappers' which can eliminate some of them.

You should not instigate NON-ORGANIC chemical controls for grubworms until you actually find these in your top-soil strata. Un-needed regular and random use of synthetic chemicals may only make control efforts more difficult as the few surviving beetles in the area might produce progeny gradually becoming immune to the routinely used chemicals.

 If random samplings of several square-foot sod patched or plugs excavated to a depth of 4-5 inches can reveal the larval forms in the roots of grass,... then using insecticidal preparations is well indicated.  Organic controls can be used at any time (see information below about Organic grubicides).

Successful grub control can usually be done in the fall when the grubs are small and near the surface. A grubicide applied in the spring and/or the fall, when the temperatures are around 65 degrees F. will kill the insects.  Synthetic Insecticidal chemicals which can be applied to top-soil to kill grub worms as well as the adult beetles include:

[01].... Sevin (also called  "Carbaryl" or "Methyl-carbamate").
[02].... Dursban ( also called  "Chlorpyrifos")
[03].... Dylox ( also called "Proxol", "Trichlorfon" or "Dipterex").
[04].... Oftanol or "Isofenphos".
[05].... Turcam (a Methyl-carbamate derivative)

Diazinon is a classic grubicide, but is becoming more difficult to find due to pesticide restrictions in some areas.  Synthetic Chemical variations/derivatives of Diazinon are also available at garden centers and these may be advertised as 'Next Generation Diazinon'.

At your lawn and garden center you should be able to find several brand-named packaged granular and also liquid-sprayable forms of grubicide chemicals.  These will also control several dozens of other common lawn and garden pests.

Some of the commercial fertilizers come with insecticidal granules in them so you can work to control insect problems while also greening up your lawn.  Some of the formula preparations can be efficiently sprayed to the lawn via a garden-hose applicator.  Check with your garden center for other insecticides you can use and any equipment you may need.


In general, insecticides applied after mid-August for the southern masked chafer grub will not be very effective.

A product called "Merit" is a new grubicide that has a longer residual than other products. Because it is a systemic, it should be applied in early to mid-July for southern masked chafer, rather than late July or early August. If bill bug grubs and/or  June-bug beetle grubs also are problems, apply Merit in late May. One application should give season-long control for all three types of grubs.

ORGANIC CONTROLS:

Non-synthetic "Organic controls" for most insect pests can be used at any time.

  A Bio-safe Organic wettable powdered form of a microbe ('Bacillus popilliae'= "milky spore", aka 'Bacillus thuringiensis' or "BT") which acts more slowly than chemicals to control more than 40 species of white grubs (especially Japanese beetles) is sold under the names of

[01]... "Doom",
[02]... "Japidemic", and
[03]... "Grub Attack".

This control measure is more long-lasting than chemical sprays.  However, using this organic control method may not achieve optimum results for several seasons while the bacteria adapt to and begin populate the root-zone making life difficult for the larvae.

  Another Organic control for grubworms consists of using beneficial nematodes. The nematode-powder (Bioquest®, etc.)  can be ordered from  biological suppliers (web-search for these) and when mixed with water it is then sprayed on to the affected area. It is important to water immediately after application. Best results are still during the mid-summer months as this is when the grub populations are at their highest.

Soil chemistry and physics has much to do with success with these ecological approaches to grub-worm problems.

With a well prepared top-soil ,... using these ecological treatments (BT and/or BN) prior to laying NEW SOD may establish an  eventual 'anti-grubworm' induced root-zone environment.  This may provide long-term organic control of these insect pest and others as well.

The organic grubicides may be difficult to find locally in your town.  Online suppliers can be found by using relevant key-words in Google Searches. Try 'organic insecticides' e.g.

Again, using one of the common "Patio-Bug Light-Zappers"  will help as it can trap and kill some of the beetles when these are active at night.  There are also commercially available pheromone (bug hormone attractant) traps.  These traps attract the insects over long distances and when combined with bug-zappers may do much to reduce local insect pest populations.

Hand-picking, crushing and disposing of live beetles any time and anywhere you encounter them can greatly reduce egg-laying and grub populations.

Also attracting beetle feeding birds, toads, lizards, harmless garden snakes and bats to your property will do much to eliminate thousands of 'bad bugs'.

As stated, Rodents eat the beetles and grubs too but should NOT be encouraged due to the other damage these mammals do to plants, crops and property and the diseases they can host.
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With a good fertile-loamy well draining top-soil, best quality hybrid grass type(s), 1-3 inches of water per week, plenty of sun-light, ...almost anyone can have an excellent lawn with a minimum maintenance effort.
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I Hope this has answered your question(s)!
Have a fantastic Summer!

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