Chafer Grubs - What, Why, How?

In recent years the devastating damage caused by Chafer Grubs on sports and amenity turf has been increasingly visible. The damage is a result of the grubs feeding on the roots of grass plants and providing a food source for badgers and birds when they come closer to the surface.

One of the influencing factors for why we are seeing an increase in Chafer Grub damage is climate change. Milder winters and warmer temperatures that have led to ideal ground conditions for the proliferation of this turf pest.  The lack of a registered effective insecticides has also meant that Greenkeepers haven’t been able to tackle them, which has enabled populations to boom.

Lifecycle

Adult beetles emerge from their pupal cases and begin to fly in large numbers at dusk from late May to June. With high infestations you’ll even see them flying throughout the day. It looks like the insect version of the Battle of Britain! Adults fly to nearby trees and shrubs where they mate on mass until dawn, at which point the adults return to the soil. Several mating flights may be made but eventually the females lay 15-20 eggs, 15-20 cm deep in the turf and hatch, over a two to five day period. These eggs will hatch in approximately 14 days. 

If moisture levels are good the grubs move up toward the surface and begin to feed on plant roots. In drier or colder conditions they may remain lower down in the soil. The grubs feed until late September when they move deeper into the soil to overwinter. However, the recent milder winters have seen them stay closer to the surface and continue to feed on the grass roots system, exacerbating the damage they cause. Being nearer to the surface for longer periods of time means they increase the time that birds spend digging up the turf to feed on them.

Pupation then takes place the following Spring (around early-to-mid-May, dependent on environmental conditions at that time) normally 5-15 cm below the surface. 

Some species of Chafer Grubs may feed below ground for two to three years before changing into adult beetles. This means that grubs may be found at any time of the year, though there will be higher numbers in Spring and Autumn.

Chafer grubs will be found at different depths of the soil depending on the time of the year too, with both soil temperature and soil moisture influencing their movement through the soil profile. This is often why some Chafer control treatments only work in specific weather conditions.

When the Chafer Grub has built up enough food reserves (usually in the Spring as the soil is warming) it grows a hard shell and transforms into a pupa. It stays in this phase for around four weeks until the outer shell cracks and the adult beetle emerges and takes flight.

Their life cycle is such that several generations can live in one patch of soil at the same time. This means that infestation numbers of the pest in the soil can increase over several years, creating more and more headaches for turf professionals.

Control

As for controlling Chafer Grubs, with the loss of certain pesticides, we now look to biological products using entomopathogenic nematodes to feed on the Chafer Grubs when they are in a juvenile stage (up to the 2nd instar growth stage), to solve the problem. These parasitic nematodes will penetrate and multiply inside these grubs and ultimately kill the grub, helping to reduce the population of these pests.

Harmonix Tri-Nema is a unique blend of three different species of entomopathogenic nematodes that work together in a resident, hunter and the explorer combination, giving three chances of killing the larvae in their different stages of growth. 

The contents and the formulation of Harmonix Tri-Nema are safe to users, consumers and the environment. There are no restrictions or safety requirements for its usage.

A few tips! 

There are some important rules to follow when applying nematodes to ensure you get the best out of them. 

• Apply the nematodes when the root zone temperatures are warm (above 12°C) for several hours a day and do not apply prior to, or during periods of heavy rain, as nematodes may be washed away.
• Apply Harmonix Tri-Nema 3-4 weeks after the peak of adult activity, this will ensure that the majority of eggs have hatched and the grubs or larvae are still in a juvenile stage.
• For areas with very high infestations, make two applications with a two-week interval between applications.
• You must refrain from applying granular fertilisers two weeks prior to and post nematode application. Moderate organic fertilisers may be applied 3-4 days before or after application.
• Excessive thatch within the turf sward may inhibit the nematodes passage into the root zone, so if possible carry out scarification to reduce thatch levels prior to application. 
  
• Aerate the turf prior to application with a sarel roller or another light aeration method such as micro or needle tines, to help the nematodes move down into the root zone where the grubs are present.
• It is a good practice to irrigate the day before application to ensure there is adequate moisture in the root zone. Nematodes are susceptible to desiccation and therefore need moisture to survive, and to aid their movement. However, do not apply prior to, or during, periods of heavy rain, as nematodes may be washed away.
• They are also susceptible to ultraviolet light, so avoid application in direct sunlight. Apply in early morning, late evening, shade or overcast conditions.
• Lightly irrigate treated areas within 30 minutes of application, to wash any nematodes remaining on the turfgrass leaves into the root zone.The root zone should be kept moist for a period of two weeks. Care should be taken not to soak the area though, as excessive irrigation could lead to drowning the nematodes; nematodes require air as well as water.
  
  Check out our video series on Harmonix Tri-Nema for a more in depth look at how nematodes work and how to use them successfully.