grubs

White grubs, a general name

Ascerno

Figure 1. Grub

Identification: White grubs is a general name for the grub (larval) stage of beetles in the family Scarabaeidae, order Coleoptera (beetles) that feed on the roots of turf (Figure 1). All species of scarab beetles have larvae or grubs that are C-shaped and vary in size depending on the species and larval age (instar). All six legs of the grub are located under the head, and the diameter of the abdomen increases slightly towards the end. In general, the grub's head capsule is an orange-black color and the end of the abdomen can be darker than the rest. Remember all grubs start small and increase in size as they molt or shed their skin and change into larger instars (larval stage). Do not treat for grubs in the fall because grubs move down into the soil for the winter. An expert can determine the species of white grub by examining the hairs and sutures on the last abdominal segment on the grub's body. In the field, identification of the grub is more difficult. However, the color and form of the adult scarab beetles are distinctive and species identification is easy. Adults often feed on tree and shrub foliage and then return to the turf for egg laying.

Damage, scouting, and management: Identify a grub problem by examining a square foot sample of lawn along the border where dead or damaged grass meets healthy grass. When grub densities are high, the blades pull away from the roots and the turf rolls back like a carpet. Skunks and moles are known to use grubs for food. However, in Minnesota night crawlers account for a sizable portion of the diet of those mammals. Therefore, grub control often will not correct damage to lawns by skunks and moles (see Extension bulletin FS-1139 for mole control). Remember the grubs turn into adult beetles that emerge from the soil and fly to trees, shrubs, and roses to feed on the leaves before returning to the turf to lay eggs. In some species, control of adults is warranted if they are damaging ornamental plants.

Another name for curl grubb is Argentine scarab inative to Uruguay and Argentina. . Larvae of this scarab were first collected lawns in Sydney (NSW) suburbs in the late 1940's The Argentinian scarab was most likely introduced by a ship tha thad previously berthed at Buenos Aires (South America). In the 1950's the Argentinian scarab had become widespread throughout Sydney being collected as far as Parramatta and in Canberra .

Egg laying occurs from mid-November through to early January. Up to 50-60 eggs are laid by the female. Argentinian scarab has a one year life cycle. Larvae may live for up to 10 months. The larval stage is from January to November. Final instar larvae feed during autumn and spring. Larval counts up to 350 insects per square metre have been recorded in Canberra.

Field grown crops:

The insect's grubs are very damaging root feeders. This causes the plant to weaken and may die in times of slight heat or water stress. This can be identified easily as effected plants loose their stability and wilt. Unless the pest is treated they will continue to feed on the roots and the plant will die regardless of water content in the soil. This is easily seen throughout the growing areas. Individual plants, which are located in areas where other plants appear to be growing well, will die. With increased populations of the insect, and the insect's grubs, increased numbers of dying plants will be obvious.

Scarab beetle grubs are also known to burrow into tubors eg: potatoes and kumara, resulting in decreased crop yield.

Scarab beetles and their grubs are considered a relatively minor pest of glasshouses. Should you see this happening in your glasshouse careful searches should be made to locate and identify the pest. It is more likely that it may be Black Vine Weevil, which causes almost identical injury and is a much more common pest of glasshouses throughout Australia.

Glasshouses:

The insect's grubs are very damaging root feeders. This causes the plant to weaken and may die in times of slight heat or water stress. This can be identified easily as effected plants loose their stability and wilt. Unless the pest is treated they will continue to feed on the roots and the plant will die regardless of water content in the soil. This is easily seen throughout the growing areas. Individual plants, which are located in areas where other plants appear to be growing well, will die. With increased populations of the insect, and the insect's grubs, increased numbers of dying plants will be obvious.

Scarab beetle grubs are also known to burrow into tubors eg: potatoes and kumara, resulting in decreased crop yield.

Scarab beetles and their grubs are considered a relatively minor pest of glasshouses. Should you see this happening in your glasshouse careful searches should be made to locate and identify the pest. It is more likely that it may be Black Vine Weevil, which causes almost identical injury and is a much more common pest of glasshouses throughout Australia.

Control:

It is of the utmost importance to wash the nematodes from the turf into the soil surface after application. Apply at dusk when damaging sunlight is at a minimum. Soil temperature must be within the range of 15-30 C. Area to be be treated should be thoroughly moistened before applying to enable the nematodes to travel on a film of moisture in the soil. Immediately after applying, water the turf again to wash the nematodes from the grass onto the soil surface.

Apply nematodes uniformly to ensure that each square metre receives the same amount of nematodes. Use a two-way drenching pattern, applying half of the total solution in each direction.

Method:

Use 1 tub for 200-250 square metres depending on the severity of infestation. Add 1 tub to at least 40 litres of water at (10-25 C), at least 10 minutes before use and stir well to suspend nematodes. Conversely use 1/5 of a tub each time to 9 litres of water i.e. 1 bucket.

A watering can (9 litres) with a fine rose (nozzle) can be used to apply the solution. Agitate or stir the suspension each time before pouring more solution into the watering can.

Apply in sections. A length of garden hose may be useful for visually marking of each section. It is also advisable to familiarise your self with how much area will be covered by your watering can by using plain water before applying nematode solution. The recommendation of 1 tub per 40 litres of water in a minimum requirement and as a rule of thumb the more water applied with the nematodes the more even the coverage will be. Ensure your application is watered in well but avoid flooding or application eveness may be affected.

NB:

Calculations of 40 litres of water per 200-250 metres squared are based on the following;

200 litres of water per 10,000 metres squared (1 ha) since a higher output will come from a watering can i.e. 200 litres water per 1000 metres squared. 20 litres water per 100 metres squared so 40 litres water per 200 metres squared.

Hint

Underfoot the turf feels spongy and soft and can be rolled back like a loose carpet due to the destruction of the roots, causing the turf to loose it's grip on the soil.

Watch birds carefully if they are paying particular attention to the turf in a specific area, it is likely there are abundant pests in the soil. Treat the area immediately otherwise the turf may be destroyed.

Larvae

Pubation

Adult

Lawn Grub

Is your grass getting circular brown areas? Is the Grass thinning?

With either of these it's a possibility that you may have lawn grubs.

There are a variety of different culprits ranging from lawn grub, lawn army worm and lawn beetle.

African black beetle larvae; causes the most lawn damage.

(above) Adult African blackbeetle.

Armyworm (common name:lawn grub) moth caterpillar feeds on turf foliage at night.

The signs can sometimes be mistaken with other pests and diseases in turf and can start off with a general yellowing before the browning. Left untreated this can rapidly lead to the death of your lawn.

Some householders encourage carnivorous birds into their garden to control the pest.

However, if the grub problem is severe, bird feeding can cause extensive damage in its own right.

For best results you will need to treat with a lawn grub destroyer.

Chemical control measures are most effective on the infant and not the adult.

As you are treating: newly hatched larvae for the lawn beetle and grub,not the adult moth, treatment may have to be repeated.

In sub tropical climates, such as ours, lawn grubs are more commonly seen between November to January - however when conditions for breeding are right you will undoubtedly see them at other times as well.

As mentioned above carnivorous birds quite enjoy lawn grub and they can be one of the first indicators there is a problem.

Another - strange as it may sound are the stingers - a variety of them from the yellow (hairy) flower wasp to the black winged red wasp - they fly low around the lawn apparently fascinated by the excess of food beneath the surface - a very good indication that treatment will be required for lawn grub.

The correct names for juvenile lawn beetle are: white curl grub, scarab beetle larvae, lawn beetle larvae or cockchafer (white curl grub is sometimes incorrectly referred to as 'lawn grub') Lawn Grub is a name commonly used for surface dwelling caterpillar such as sod webworm, army worm and cutworm, which become moths.

The second and third phase of the Lawn beetle life cycle can be the most damaging ( the larger of the four larvae pictured above left) as they feed quite vigorously on roots and underground stems. These African black beetle can establish in a wide variety of grasses from green & blue couch to soft leaf buffalo and kikuyu.

Control is most effective when activity is monitored - one way is to place a damp hessian bag or piece of carpet on the lawn at night - in the morning adult beetle can be collected and disposed of.

It is believed that garden lighting although handy to spot the adult beetle also attracts them and may have the unwanted side effect of increasing egg laying. Turning off as many garden lights as possible may assist in keeping numbers down.

Chemical treatment is most effective on new larvae - prior to treatment; water the lawn well to encourage them to come closer to the surface - this will enhance the benefits of the treatment meaning it will not have to penetrate as far through the soil to reach the larvae.

There is a variety of product available for treatment from the larvae to the bug - we are more than happy to help you make the best selection from our range for effective treatment.

Posted by The Zeal Group. Call us on 1300882787