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All About Grubs

 

White grubs can cause serious damage to home lawns. In their adult stage, they can also damage deciduous trees, shrubs, annuals and herbaceous perennials. This two-fold attack makes it imperative to pay attention and do something if grubs make their home in our gardens.

White grubs are the larval stage of Japanese Beetles, European Chafers or June Bugs. The grubs are all slightly different in appearance but for the purposes of control or management, they can be treated the same way. The grubs are whitish, with dark, yellowish-brown heads and three pairs of legs. They vary in size from 1 cm to 3 cm in length.

To understand the best method and timing of control, it is important to know the life cycle of these insects. The adult beetles emerge from the pupal stage in the soil in late June. Adults feed on deciduous plants and lay their eggs in the soil until they die in about mid-August.

The eggs hatch into small grubs from late July until early September. These grubs feed on grass roots and become progressively larger into the fall. As the cool weather approaches the grubs move farther down into the soil to protect themselves from winter conditions and over winter about 12 inches beneath the soil surface. In late April the grubs move towards the soil surface again and resume their feeding until they go into their pupal stage in early June. A new crop of adults emerge to start the next life cycle.

One common tell-tale sign that you have a grub problem is when skunks or raccoons dig up the lawn in search of grubs. Another sign is when your lawn has large dead patches which can be rolled back like a carpet and no amount of watering will bring it back. Badly infested turf can be completely killed by grubs, requiring the installation of a completely new lawn.

By cutting out a square foot of sod to a depth of 6-10cm and examining it, you may readily determine whether it is seriously infested with grubs. The presence of five to ten grubs would indicate a light infestation, but enough to warrant treatment. A count of thirty to fifty would indicate a very heavy infestation.

It is often recommended to treat for grubs in early spring to prevent the emergence of adults. This is a less effective time for control since the grubs are large and are not feeding as actively.

The best time to control grubs is when they are small and close to the surface. This ranges from late July until early September. The control method you use can be a granular insecticide/fertilizer combination, a liquid spray application of an insecticide or by using parasitic nematodes as a biological control.

Whichever method is used make sure the soil is moist prior to application and is well watered afterwards. The water is required to move the control products down to where the grubs are feeding underneath the grass roots.

Parasitic nematodes are microscopic worms which infect and kill grubs. They are purchased as a sponge which contains millions of nematodes. The contents of the sponge are mixed with water and applied to the turfgrass surface in a similar fashion as an insecticide spray. Soil moisture is very important when using nematodes since they will die in drought conditions. The nematodes will not overwinter in the soil so will need to be re-applied every year.

The beetle which is the most damaging in its adult stage is the Japanese Beetle. It is about 2 cm in length and is a metallic blue-green colour with copper wing covers. It is very cumbersome insect with poor eye sight and will only travel short distances at a time. It has a keen sense of smell and is quick to find roses, cannas, marigolds and the other plants it prefers to eat. The adult beetles generally fly when air temperatures are about 21 degrees C, so look for them in the early morning and late afternoon. They will skeletonize foliage and make Swiss cheese-like markings through flowers. Linden, Boston Ivy, Virginia Creeper and Grapes are some other deciduous plants which it attacks. These adults can be controlled by insecticidal sprays which are best applied during the time of beetle flight. Killing the adults will also reduce the grub population for the fall and the following year.

 

Daisy Moore, 1999.

 

 

Other summer garden tips:

(click on the tip you want to read)

 

Extreme Conditions
Growing Roses
Summer Lawn Care
Propogation by Cuttings
Sources of Native Plants
Making Sense of Fertilizer Labels
Annual/Perennial Combinations
Climbing Plants
The Dry Garden
Wildlife
Ornamental Grasses
Chooosing A Good Gardening Book
Companion Planting
Preparing the Compost for Fall Use
Getting the Most out of your Vegetable Garden
Repairing Lawns From Summer Stress
All About Grubs
All About Onions
Useful Herbs for the Home Garden
Screens and Hedges


 

 

 

Home  |  Garden designs  |  Naturalized gardening  |  Help with your garden  |  Garden Tips Spring  Summer  Fall  | Contact Daisy

 

Daisy Moore 2005