The landscape for insect pest control has changed. The two main insecticides that we used for the control of Leatherjacket and Chafer Grubs have been taken off the market writes Henry Bechelet.
The authorisation for the disposal, storage and use of the active ingredient imidacloprid (used for the control of Chafer Grubs) ends on 31 October 2016. For chlorpyrifos (used for Leatherjacket control) the authorisation ended on 31 August 2015 for use on amenity grassland and managed amenity turf. By the end of the year there will be no approved chemical control methods for control of Chafers and Leatherjackets in UK amenity grassland and managed amenity turf sector. So what will we do?
At this stage it is unlikely that there will be any new insecticides available for the control of such potentially damaging insect pests as Leatherjackets and Chafer Grubs BUT there is an effective biological control option already available. The products Nemasys G and Nemasys J are effective against Chafer Grubs and Leatherjacket Grubs but you will need to use them differently than the insecticides to get effective results.
Nemasys G (controls Chafers ) and Nemasys J (controls Leatherjackets) contain actively predatory nematodes that provide biological control of the grubs by entering and feeding on the larvae, which stops them feeding within three days of infection. The nematodes complete their life cycle within the larvae, then enter the soil seeking out more hosts, so the pest control continues naturally.
The normally invisible to the eye nematodes contained in the Nemasys products, shown here at a very high magnification.
Nemasys G contains the indigenous beneficial nematode Heterorhabditis bacteriophora which feeds on Chafer Grubs. Nemasys J contains the beneficial nematode Steinernema feltiae which seek out Leatherjackets. Both are available in a pack of 250 million nematodes which treats 500m2 (in 50 litres of water). Both products come in a water dispersible carrier and are manufactured in the UK.
The factory in the UK where the nematodes are manufactured
The garden chafer is the most important chafer pest of lawns and sports turf, occurring in large numbers and causing considerable damage due to the grubs feeding on the grass roots. It is found throughout the UK and is more abundant in the warmer and wetter regions, i.e. South West. Birds, badgers and foxes are significant predators, often tearing up turf to find the grubs. Adults are 7-12 mm long with a bright green head and thorax, long outstanding pubescence and brown wing cases. Adults emerge from the ground in May/June and mate. After mating the females burrow into the turf to lay their eggs 10-15 cm below the soil surface. The eggs hatch out four to five weeks later into larvae forming characteristic C-shaped grubs, staying close to the soil surface until early October after which they move deeper to overwinter.
Leatherjackets are the larvae of crane flies, also known as daddylonglegs (Tipula spp.). The adult insect as its name suggests, has long thin legs, a small thin body around 25mm in length and one pair of wings. Crane flies cause no damage to plants since the adults do not feed. Mating and egg laying begins a day after the adults emerge. Tipula paludosa is the most abundant crane fly in Europe and is usually seen flying from early August to October (one generation per year). Tipula oleracea can fly longer distances and complete two generations per year with one flight in August/September and another in May/June. Eggs are laid in late August and hatch within two weeks. The young grubs start feeding immediately, however, direct and indirect damage is most likely to occur in the spring when the mature grubs feed after overwintering in the soil.The biggest challenge for nematode application into turf is to get the predatory nematodes in contact with their target when the grubs are small and feeding close to the surface. This means treating the turf at an early stage of the pest life cycle, in late summer and early autumn (and before the symptom of any damage has occurred). You will need to keep monitoring for Crane Fly activity or Chafer Beetles on the wing (or go on past experiences) to determine the need to spray. Also, the soil temperature needs to be above 12oC for the nematodes to be actively predatory and they will only be able to move and survive if there is adequate moisture in the soil (>15% VMC). Although this might sound prohibitive this means that you simply need to treat areas that you suspect are infested as soon as you can, when soil conditions are appropriate.
The left image shows damage to the course, the right is taken in the following year, following Nemasys treatment
In terms of making the application you need to take a step by step approach. Prior to application, ensure the turf is mown and spiked and that the entire soil profile is damp at the time of treatment. Avoid applications in bright sunlight because intense UV light will kill the nematodes. Apply in the evening or in dull conditions, ideally during rainfall. Mix the entire contents of the pack in a bucket of water to create a stock solution and stir vigorously. Once mixed pour the solution into a half filled sprayer fitted with a coarse spray nozzle (filters removed) and fill with water. Tank-mixing with a compatible penetrant wetting agent such as H2Pro Maximise can aid quick penetration of the solution and nematodes down to the grubs. Do not store stock solution overnight and so apply any remaining solution to the affected lawn (you cannot over apply nematodes).
After application watering the treated area thoroughly will ensure that the nematodes have been washed off the grass leaf and through the thatch layer. For the following two weeks continue to irrigate as is appropriate to ensure the soil profile remains damp.
Leatherjacket and Chafer Grubs are a potentially serious pest of turf. Because insecticides are being taken off the market we need to rethink how we go about achieving control. Insect parasitic nematodes are an effective control for Leatherjackets and Chafer Grubs but you will need to apply them at the right time in the pest lifecycle in appropriate environmental conditions. If you take care with the use of Nemasys G and Nemasys J then you will be able to keep on top of potentially damaging pest attacks.Biological control is effective, safe to the environment and the future of Leatherjacket and Chafer Grub control.