Trouble With Grub Worms? When To Treat For Grubs!

White grubs are a common nuisance in gardens throughout the world making lawn care more of a challenge. Also called grub worms, the small critters resemble little white worms.

curled up grub wormsPin
MiLiia| DepositPhotos

The grub is not a worm. It’s the larvae of various species of scarab beetles. 

The Scarabaeidae (Scarab) family of beetles includes over 30,000 species.

The most common beetles include:

These pests may appear in parts of North America, Europe, and Australia.

Grubs tend to feed on the roots of plants and lawn grasses, causing severe damage to gardens and lawns. 

To keep grubs from destroying a garden, learn how to identify and treat the problem.

What Are Grubs?

Grubs are the larvae of scarab beetles. 

Many scarab beetles like Japanese beetles are scavengers mostly feeding on decaying plant material, making them a common sight in gardens. 

The C-shaped larvae mostly live underground or under plant debris, feeding on roots.

What do grubs look like? The small grubs are white or pale yellow and measure just 1″ or 2″ inches long.

  • Japanese beetles are the most threatening species as the beetles may also feed on plants. 
  • Adult female beetles live on plants during the day and return to the soil to lay their eggs at night. 
  • Egg-laying mostly occurs throughout early July with eggs typically hatching in late July.
  • The eggs develop into white colored grubs by late summer (August). 
  • The grubs dig into the soil throughout the winter and start to move upward as the temperatures warm in early spring.
  • In September and October, the grubs are still close enough to the surface to start feeding on the roots of plants. 
  • They mostly go dormant during winter and start feeding again in April and May. 
  • By June, the grubs develop into a pupa and emerge as adults in late June or early July to repeat the cycle.

Grub Damage – What Damage Do Grubs Cause?

As grubs feed on the roots of plants, they slowly kill plants from underground. 

Without healthy roots, the plant cannot obtain nutrients and moisture from the soil.

Unfortunately, it’s not easy to detect the damage caused by grubs until the foliage and stems start to suffer. 

Grubs may feed on any roots in the garden or lawn but tend to prefer the roots of lawn grasses, strawberries, corn, and many other species of vegetables and fruits. 

If grubs infest the lawn, large dry patches of dead grass may eventually appear.

grub larva feeding on rootsPin
Japanese beetle and June beetles grubs enjoy feeding on roots – knjo | depositPhotos

Grub Control – How to Prevent Grub Infestations

There are several methods for limiting the risk of grub infestations including the grub killer product called Grubex from Scotts.

Read our article on What You Need To Know About Controlling Grubs with Scotts Grubex.

While these methods may not provide complete protection, they help create a less hospitable environment for adult beetles. 

  • This may limit the number of eggs they lay in the lawn or garden.
  • Avoid over-watering the lawn or garden. 
  • Moist soil provides an ideal environment for egg-laying. 
  • Decreasing the water retention of the soil also helps limit moisture. 
  • Irrigate gardens and amend the soil with sand or perlite to increase drainage.
  • Removing plant debris also helps limit the risk of infestations. 
  • Clean up dead leaves and decaying plant material throughout the year, especially during the summer when adult beetles start to lay eggs.

How To Treat for Lawn Grubs

If lawn grubs have already infested a garden or lawn, the best grub control treatments involve the use of insecticides. 

Insecticides should be used at specific times of the year as the growth stage and life cycle of the grub may impact the effectiveness of the treatment.

In the fall and spring, grubs are large and difficult to kill with insecticides. 

The best time period for applying insecticide is May to July when the eggs are starting to hatch.

If 10 or more grubs per square foot at found repeated applications are often needed to eliminate grubs. 

The following insecticides are known to help control grubs:

Some of these insecticides are highly toxic to birds, fish, and other species. 

Read the warnings on the label before applying.

The insecticide is typically applied directly to the infested areas and allowed to soak into the soil where it can kill the grubs. 

Insecticides may also be used to target adult beetle populations, which may limit the number of eggs hatched during the summer.

Another solution is the use of nematodes. 

Nematodes are small critters resembling roundworms. 

While some species of nematodes may damage plants, steinernema riobrave and heterorhabditis bacteriophora varieties are safe to use in gardens.

Nematodes help get rid of grubs, adult beetles, and a wide range of additional garden pests. 

Mix the nematodes with water and apply them to the garden with a sprayer. 

Reapply the nematodes every few days. 

It may take several weeks to completely kill the grubs and beetles.

If these solutions don’t work, try applying milky spore to the garden. 

Mix milky spore powder with water and apply the mixture to the garden and plants. 

If you click this link and make a purchase, we earn a commission at no additional cost to you.

While milky spore isn’t proven effective for treating grubs in lawns, it’s known to help treat grub infestations in gardens.

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