Overview
What are White Grubs?
What insects to White Grubs develop into?
What is the impact of White Grubs?
How do I know if I have a White Grub problem?
How do I get rid of White Grubs?
Conclusions and further directions
White grubs are the larvae of different scarab beetle species. They live in the top layer of soil and feed on the roots of grasses, where they can have a destructive impact on crop health if not properly controlled. White grubs have a wide geographic distribution, and different species are more prevalent in certain areas. The white grubs of scarab beetles have become a particular issue in India in recent years, and turfgrass is particularly susceptible to damage caused by these insects. Fortunately, white grubs are susceptible to several management strategies, including chemical controls like insecticides and biological controls like insect parasitic nematodes.
This article provides everything you need to know about white grubs, including the different types and how to deal with infestations effectively. First, let’s talk more precisely about what white grubs are and how to identify them.
What are White Grubs?
White grubs are the larval stage of different types of scarab and chafer beetles, which belong to a family called Scarabaeidae. As the name suggests, these grub insects are creamy-white but have red/brown heads and are normally found in the typical “C” shape. Their size varies depending on the species and age but typically ranges between 6 and 50mm.
Most white grubs complete their life cycle over one year. Typically, adult beetles mate and lay eggs during summer. After the eggs hatch, the white grubs feed on roots until the winter months. The cold weather causes the beetle larvae to move deeper underground, where they remain dormant, away from the root zone. As temperatures increase, the grubs resume eating roots before maturing into adults and laying eggs in the summer. Some species have two life cycles per year, while others have one cycle every two to three years. Now, let’s look at the different white grub species.
What insects do White Grubs develop into?
There are around thirty thousand species of scarab beetle. Fortunately, only a few of them are considered pests. Below is a description of the most important species that cause damage to grasses.
Masked Chafer (Cyclocephala spp.)
These beetles belong to the genus Cyclocephala and have a wide geographic distribution across India and the Americas. White grubs of these species are typically 25mm long and can cause damage to different grasses, especially during dry seasons. Adults are light brown with dark-colored heads and usually have a one-year life cycle.
The European Chafer (Amphimallon majale)
This species is native to Europe but is now found throughout North America. The white grubs of European chafers are around 22mm in length and feed on the roots of grasses in cooler climates. Adult European chafers are red-brown in color, and the species has a one-year life cycle.
June Beetles (Phyllophaga spp.)
These beetles are dispersed throughout North America and have two- to three-year life cycles. They belong to the scarab subfamily Melolonthinae, and adults are brown/red. White grubs of these species cause damage not only to turf grass but also to other plants like Christmas trees.
Black Turfgrass Ataenius (Ataenius spretulus)
As the name suggests, adults of this species are black and typically affect turf grass. They are found in North America and may have multiple life cycles per year, depending on the climate. White grubs of this species are smaller than others, typically reaching a quarter of an inch in length.
Japanese Beetle (Popillia japonica)
This species originates from Japan and is now invasive in Europe and America. Adult Japanese beetles have metallic green heads and brown wing covers and can cause damage to the leaves of different plants. The white grubs of Japanese beetles feed on the root system of grasses and can reach 25mm in length.
What is the impact of White Grubs?
The most common damage caused by white grubs is to grasses, mainly turf grass. These grub insects have strong mandibles which allow them to feed on roots. Root damage prevents grasses from absorbing nutrients and water from the soil, causing them to dry out and die. For this reason, white grubs can be particularly damaging in dry seasons when water is scarce, and their effects share common characteristics with drought stress.
Infestations of white grubs can also attract large digging predators like foxes, badgers, and magpies, which can cause further damage to grasses and lawns.
Do White Grubs Sting?
No. White grubs do not bite or sting humans. They are not poisonous or known to carry any diseases.
How do I know if I have a White Grub problem?
As mentioned above, early stages of white grub infestation can mimic signs of drought stress, namely the emergence of brown patches that grow and eventually join up.
Signs of a large infestation include spongy soil and grass that peels off the soil like a carpet when pulled.
Depending on the species, white grubs can be easily spotted in the root zone of the soil. Sampling the soil for white grubs is essential for determining the extent of the issue and the type of control required, if any.
How to sample soil for White Grubs
Select five random sections of grass and remove approximatively 30 liters of soil. Look for white grubs in the sampled soil using dark-colored plastic or another material. The presence of two or more white grubs per 30 liters of soil, in addition to drought symptoms, can mean the presence of a damaging infestation. If you have a white grub problem, read the following section for some excellent strategies to control it.
How do I Get rid of White Grubs?
Cultural Practices
Reducing how much water you give to grasses in the summer sounds like it will cause further damage, especially when there are already signs of drought stress. However, less watering can encourage root growth and prevent the more harmful effects of white grub infestations. Frequent mowing is also an effective strategy for promoting the growth of roots.
Biological Control
Bacteria biopesticides and nematodes offer good biological control solutions to these insects without damaging the plant. Milky spore disease is a bacterial infection of white grubs that leads to the death of the grubs. Bacteria of the species Paenibacillus popilliae (also known as Bacillus popilliae) can be safely added to grass or crops to deal with white grub problems.
Entomopathogenic nematodes are tiny worms that feed on white grubs and kill them. These nematodes can be added to soil using similar methods to chemical controls. However, they do not cause long-term damage to soil and the environment like chemicals do.
Chemical Control
Insecticides can be effective against white grubs but should be considered a last resort. Chemical control options can cause significant harm to people and the environment. If necessary, insecticides should be applied to the root zone of grasses in the late summer when the grubs are still small. Check local pesticide lists for registered products and always read the label.
For a scientific breakdown of the efficacy of different solutions to white grubs, you can look at this review from Morales-Rodriguez et al. (2010).
Conclusions and future directions
White grubs are significant pests that damage grasses, especially turf grass, by feeding on root systems. They have a wide geographic distribution and are a growing concern, especially in India, where the masked chafer species is prominent. These insects are easily identifiable, though determining the precise species can be difficult.
Symptoms of white grub activity are similar to drought stress, and performing a randomized screening of grass sections is the surest way to know if you have a significant infestation.
There are many treatment options for dealing with white grub problems, ranging from changing watering regimens to biological and chemical approaches. Like many pests, white grub infestations are more easily resolved when caught early. Be on the lookout for the signs we’ve mentioned above, and if you have a white grub problem, consider using an integrated pest management approach to resolve it.
For more information on different types of pests, you can consult the CABI BioProtection Portal resources. To help find the best solution for your white grub problem, visit our products page.
