Key Points 

  • Fall (August to September) is the best time to control grubs. At this time, they are still small and near the surface where pesticides can get to them.
  • Spring is a more difficult time to control grubs. They are larger and are found at different depths in the soil following the winter months.
  •  Do not assume that you have grubs. Always check by rolling back a piece of sod in the suspected area. Look in several locations.
  •  Treat grubs only when you find them near the surface (top 3 or 4 inches of soil) and in large numbers (5 to 10 per square foot).
  •  Insecticides used for grub control must be watered into the soil following application to be effective.
  •  You should monitor the lawn again in early September. Fall is when the next generation of grubs gets started.
  •  Always follow pesticide label instructions carefully. Be sure to keep children and pets off treated areas at least until the spray dries. Twenty four hours would be even better.

What are Grubs?

Grubs are the immature form of several beetles including June bugs, Japanese beetles, rose chafer and European chafer. They are generally white to grayish in color with dark heads and six legs. They may grow from 1/2 to 3/4 inch in length.

The one causing the serious problem is the European chafer.

 Diagnosing the Problem

The key to success is the proper identification of the problem. For grubs to cause the death of the grass, they must be present in large numbers. So, diagnosing the problem is not difficult.

Take a sharp tool such as a knife or shovel and cut a wedge in the turf about 12 inches on a side. Roll back the sod and count the grubs in the root zone of the grass.

In a lawn that is not routinely irrigated, 5 or more grubs per square foot may be enough to kill the grass. Highly maintained lawns that are routinely fertilized and have automatic irrigation systems may be able to withstand 15 or more grubs per square foot.

Two or three grubs per square foot will not cause significant damage and do not warrant treatment.

European Chafer Life Cycle

August Eggs hatch and young grubs begin to feed on grass roots.
November As the soil cools, grubs dig deeper into the soil for the winter.
April As the soil warms, grubs move toward the surface and resume feeding on grass roots.
June In late June, the grubs change into beetles.
July The beetles emerge from the ground in the evening, mate in trees and lay their eggs in the soil in nearby lawns.

  Control Alternatives

 Chemical Controls

There are several insecticides labeled for grub control in the home lawn. These chemicals control the grub form of the insect and may be applied as a granule, in a liquid spray or may be in combination with fertilizers.

Regardless of the form used, the insecticide must be watered into the soil immediately after application for best results. This means applying about 1/2 inch of water so that the insecticide moves down 3 or 4 inches into the soil to the grubs.

Products with the active ingredients, Merit or Mach II, work best on newly hatched grubs. Unlike the other insecticides, these products must be applied in June or early July for best results.

Follow the label instructions closely for best effects. Keep all pets and children off the area for at least 24 hours (longer if possible) to minimize exposure.

 Other Alternatives

Milky spore disease is sometimes mentioned as a control for grubs. Unfortunately, the effectiveness of this product when used on lawns has not been shown. Studies indicate that it may take 2 or 3 years after application to become established in northern lawns, if at all.

Another non-chemical product called Biosafe contains parasitic nematodes (microscopic roundworms) that attack the grubs. This product may be difficult to apply with home spray equipment and must be kept moist by regular irrigation. It is also not readily available.

 Cultural Alternatives

Keeping the lawn watered regularly during hot, dry weather may help minimize grub damage. However, once you start summer irrigation, you should continue it until fall or the grass will be under even greater stress if watering is stopped during the hot part of the summer.

 When To Control Grubs

 The grubs hatch in August. Therefore, the fall is the best time to attempt control.

Spring control is more difficult because the grubs are large and may be at different depths in the soil. The temptation is to treat the soil too early before the grubs have moved close to the surface again.

To be sure the grubs are near the surface, you must monitor by turning over the sod and looking for them.

Avoid routine and repeated use of insecticides on the lawn. This often kills beneficial insects and may be detrimental to the environment. This can lead to even greater insect problems in the future.

What To Do With Bare Spots in the Lawn

 Bare spots in the lawn will need to be reseeded or weeds will take over. Autumn, between mid-August and mid-September, is the best time to plant grass seed. Early spring (around tax time) is the second best time. However, spring is more difficult because the tender seedlings will emerge just before the hot days of June and July.

Work the soil with a rake or rototiller to loosen it. Spread grass seed at the rate of about 4 pounds per 1,000 square feet.

Use a mixture of Kentucky bluegrass, fine fescue and perennial ryegrass for a general purpose lawn. Use shade tolerant mixtures for low sunlight situations.

Rake the seed into the soil and tamp it gently with the end of the rake or, use a light roller(minus the water).

The key to success with new grass is to keep it watered throughout the entire first season. Cover the newly seeded area with a thin layer of straw to help conserve moisture. Newly seeded beds may need to be watered twice daily during hot weather.

Provide at least 1 inch of water in the form of rain or irrigation per week throughout the first growing season. This is critical for establishment of new turf.

When the grass is 2 inches tall, remove half of the straw. The remainder will decompose over time.

Mowing may begin when the grass is about 3 inches tall. Cut to about 2 to 2.5 inches and be sure that the mower blade is sharp. Dull blades will batter the young plants and pull them out of the ground.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.


Types of Insects

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