This spring we learnt of the loss to the Amenity market of the insecticide chlorpyrifos, currently used to prevent damage to turf on sports and recreational turf. Chlorpyrifos, previously sold under a variety of brand names such as ‘Cyren’ and ‘Ballad’, was used to control the Crane fly larvae or ‘leatherjackets’ as well as Frit fly and two other minor insect turf pests classified as Bibionid flies; the St Mark’s Fly and the Fever Fly. Notice of withdrawal for the amenity use of chlorpyrifos was issued on 19 May 2015, with no further use on turf after 31 August 2015.
To explain this sudden decision, the UK Government’s Chemical Regulation Department gave the reason that: -
“As part of the European Union’s routine review programme, new human health based safety levels (known as ‘end points’) have been agreed for chlorpyrifos. These new end points represent the latest assessment of risk against modern regulatory standards. Where the risk assessments have identified current uses that can no longer be supported, HSE are taking the precautionary approach of restricting those uses with immediate effect”.
There is no alternative insecticide treatment for leatherjackets, so control of will now require a fundamental change in management practices. In this short article I will look at the biology of the Crane fly and the use of alternative biological control methods.
Crane flies belong to the family Tipulidae, which contains over 15,000 species worldwide. There are reported to be around 300 species of Crane fly in the UK alone. The most common species found causing problems in UK turf situations is Tipula paludosa with two other species; T. oleracea and T. vernalis encountered occasionally. Leatherjackets, cause stress and damage to grass plants by feeding on the roots and stems. Extensive areas of turf can be turned yellow as a result of the grub’s feeding habits and this is often made worse by secondary predators; large birds, badgers and moles, ripping up the turf in search of the grubs. Leatherjackets also feed on the roots of many other plants (ornamentals, fruit and vegetables). They are legless, grey-brown, fleshy grubs, growing to a size of up to 45mm long with tough wrinkled skins and a number of small, pointed protuberances at the tail end.
Crane fly larva – known as a ‘leatherjacket’
The Crane Fly is well distributed through all areas of the UK, although certain species are better adapted to the far northern climate. They prefer damp wooded locations, streams, water margins and flooded areas and are most active during the early evening when temperatures drop. Adult Crane flies, affectionately known as the ‘Daddy Long-legs’, can be seen from late spring through to autumn with the majority emerging in late August and early September, depending on the weather . The female has a distinctive pointed ovipositor at the end of the abdomen, which is used to penetrate the ground during egg laying.
Crane fly male Crane fly female
The life-span of an adult Crane fly is relatively short, about 14 days and in that time they must pair up and mate before the female can lay her eggs (about 300) just below the turf surface. With the right conditions of temperature and moisture, the eggs will hatch in 10 to 14 days releasing the first larval stage into the soil. At first the young grubs are too small to have much effect on grass health but as time progresses they grow in size and appetite. They usually undergo two moults before the onset of winter when soil temperatures fall. At this time the larvae now in their third stage stop feeding and move deeper into the soil to survive the cold. Long periods of extremely low temperatures (< -1°C) during the winter months will dramatically thin out the numbers of leatherjackets that survive into the following spring. Conversely, mild winters allow more to survive to adulthood and where we see several consecutive mild winters, the population of the Crane fly can reach alarmingly high numbers.
When soil temperatures begin to rise in the spring, the over-wintered larvae start to feed again and this is when they do most damage to turf. After the fourth larval stage is reached the hungry grubs engage in a feeding frenzy and this often coincides with the breeding season of secondary predators who, due to the much weakened grass root structure, are able to roll back the turf like a carpet to find the grubs, which make a good meal for their offspring. Very wet weather can cause local water-logging, often bringing hundreds of larvae to the surface. Leatherjackets continue to feed during the summer and complete their life cycle when they emerge as adults shedding the brown pupal case on the surface.
Control measures.
Small grassed areas infested with leatherjackets can be ‘harvested’ by soaking with water after sundown and then covering overnight with a material impervious to light such as black polythene. This encourages the larvae to come to the surface where they can be collected and destroyed. This method is most effective in warm temperatures when there is sufficient soil moisture and the leatherjackets are feeding close to the surface. The covering material should be slowly peeled back in the morning to reveal the emerged grubs. It is important not to uncover too large an area at a time for collecting purposes, as the grubs will move back into the soil when exposed to daylight.
Without insecticides to control the Crane fly larva, we will have to rely on the use of the entomopathogenic nematode Steinernema feltiae to reduce the number of leatherjacket grubs in the soil. Applied as a drench with a sprayer, the nematodes move through the moist soil to find a Crane fly larva and enter the body, where they multiply and release a strain of bacteria that kills it. The dead larva rapidly decomposes, releasing more nematodes into the soil, which can then infect new hosts. To get the best results from using nematodes, they need to be applied carefully following all supplier recommendations. The main points are listed below: -
1) Upon receipt of the nematodes, use them immediately or store in a refrigerator at 5°C. DO NOT FREEZE.
2) Use the entire contents of each pack at one time. Do not split or subdivide individual packs as each contains a measured dose of nematodes. Do not store diluted product.
3) Ensure that the turf to be treated is thoroughly watered before and after treatment so that the nematode worms can move freely in search of the target grubs.
4) It is best to apply on a dull day or in the evening to avoid exposing the worms to sunlight or high surface temperatures.
5) Make sure the application equipment is thoroughly cleaned before use, removing any traces of chemicals using a proprietary tank cleaner and plenty of water to rinse.
6) It is advisable to remove all fine filters (50 mesh or smaller) from the application equipment, including the nozzle filters.
7) Mixing. Partly fill the sprayer tank with cool, clean water. Start the agitator and keep it running until the application is completed. Empty one pack of nematodes into a bucket containing a minimum of 10 litres water and stir the contents thoroughly making sure the entire product is mixed before adding it to the partly filled spray tank. Top up the tank to the required level. Apply immediately, keeping the suspension of nematodes agitated during application.
Nematodes are effective in soils between 12-20°C and the ideal time for this treatment is early autumn – after the crane fly eggs have hatched but before the soil cools below 12°C. These microscopic nematode worms are available in trays sufficient to treat 500m² (with smaller packs available on the retail market at a premium price). The product has a limited shelf life (up to 8 weeks in low temperature storage) and must be used before the expiry date.
Parasitic nematode Steinernema feltiae Nematodes infecting fly larva