White grubs are the larvae of beetles. The larvae all have six strong legs near the head, and are white. They vary in other characteristics such as size, head color, and hair patterns on the body. These grubs feed on roots of various plants. Your garden plants, lawn and even potted plants can be attacked by grubs.
In general, white grubs have a one or two year life cycle, depending on the type of grub. The following describes a one year life cycle.
Spring - The grubs are fully grown larvae and are actively feeding.
Summer - The grubs turn into pupae and pupate into beetles. This generally occurs around June in the northern US and Canada.
The beetles only live for about a week, mating and laying eggs. These eggs hatch a few weeks later.
Fall - The new grubs feed until temperatures drop and they burrow deep in the soil to avoid freezing, and emerge the following spring.
Many grubs only cause minor damage and control strategies are not required.
There are a few grubs, like European Chafer, that commonly cause extensive damage to lawns. The grubs eat the roots of the lawn, and the lawn dies. As few as five grubs per square foot can cause extensive damage.
Major damage can also occur when raccoons, skunks, and crows rip the lawn apart while feeding on the grubs.
The most important thing to do to reduce grub damage is to ensure a healthy, robust lawn. This means regular feedings and annual core aeration to encourage a strong, dense root system. If the lawn has a dense root system, it will tolerate minor feeding by the grubs.
Traditional Pest Control
If the lawn has historically had large populations of grubs like European Chafer, then consider scheduling an application of Merit® in June or July. Merit® is a new grub control product that must be applied prior to hatching of the new eggs. It provides up to 90% control of the grub larvae and meets all the new environmental standards imposed by PMRA (Health Canada).
Note - Check with your local Nutri-Lawn if Merit® is registered in your area.
If it is spring time and the lawn is being damaged by grubs, then applications of Sevin® will help reduce the grub populations.
It is important to know that controlling fully matured grubs in the spring is very difficult for several reasons.
1. The grub’s immune system is fully developed, and it must consume more of the pest control before control is successful.
2. The grubs may not be actively feeding due to cooler soil temperatures, and they may not consume enough of the pest control to be effective.
3. The grubs are often deeper in the soil, and getting the pest control deep enough into the soil for effective control is difficult. Core aeration will facilitate the movement of the pest control to the grubs.
Because of these factors, the best strategy is to focus on renovating the damaged areas in late spring, and schedule a Merit® application for June.
Note - Check with your local Nutri-Lawn if Sevin® is registered for use in your area.
Beneficial Insects - Predatory Nematodes
Predatory nematodes are naturally occuring microscopic roundworms that attack soil larvae like white grubs. They are best used as a preventative application applied to newly hatched larvae. This means that the best time to apply the nematodes to white grubs like European Chafer is in late August into early October depending on geographic location.
The nematodes will not control all the grubs in the soil, but will reduce the grub populations and thereby reduce any potential lawn damage.
They are naturally occurring in the soil, but we inundate the soil with the nematodes in order to achieve infection of the larvae.
There are a few factors to consider when applying nematodes.
1. Apply the nematodes to moist soil. If applied to dry soil, the nematodes will die. We recommend a heavy watering prior to the application of nematodes to not only wet out the soil and thatch, but also to drive the grubs closer to the surface and closer to the nematodes.
2. Avoid applying nematodes during bright sunny days. UV light kills nematodes, so it is best to apply them early or late in the day when light levels are low, or during an overcast day.
3. Water the nematodes into the soil as soon as possible. Water carries the nematodes off the leaves of the lawn into the soil where the grubs live. Core aeration prior to an application will facilitate the movement of the grubs into the root zone.
Animal Damage - Raccoons, Skunks, and Crows
Raccoons, skunks, and crows love eating white grubs. They must taste like the finest prawns because these animals will dig, scratch and peck all night in order to have a feast of grubs. Often the grub population is not high enough to cause significant damage, but the animal feeding results in extensive damage.
The best strategy is to chase them off your lawn. This can be accomplished with a motion detector sprinkler. The sprinkler can be set to spray water when anything moves within its field of view. Raccoons don't like getting wet.
They can be purchased at Lee Valley Hardware.
A dog would be another option; however, it seems a little extreme. There is also the skunk factor to consider. Dogs and skunks generally do not get along well.