Leatherjackets

Leatherjackets

By Dr Ruth Mann -STRI

Leatherjackets are the second most widespread pest problem on golf courses in the UK and Ireland (Mann, 2003) and throughout the majority of Europe. Unfortunately, little research has been carried out into leatherjackets infesting turfgrass. Most work has been concerned with forage grass. A review of work carried out into leatherjacket problems in grassland was written by Blackshaw (1991) and has been used throughout this report. Leatherjackets are a major pest in grassland leys, lawns, golf courses, sports fields and arable crops (Anon, 1984).

Reports of leatherjackets damaging grassland or turf in England, Ireland, France, Germany, Netherlands, Norway (Blackshaw, 1991) and cool season turf areas of USA and Canada (Potter, 1998) have been published.

Leatherjacket biology

Leatherjackets are the larvae of the crane fly (Tipula spp.), more commonly called the daddy-long-legs (Plate 2). There are numerous species, such as Tipula paludosa, T. oleracea, T. variipennis, T. vernalis and T. subnodicornis (Blackshaw, 1991). Only T. paludosa and T. oleracea are recognised as a pest throughout Europe and T. paludosa is cited as the pest species found in US and Canada. The lifecycle differs depending on the species.

Leatherjacket (Tipula spp.)

Tipula paludosa emerge as adults in August and September (Blackshaw, 1991). Females do not move far from emergence and mating occurs quickly with eggs being laid within 32 hours of emergence. Larvae enter a resting phase in the summer before pupation which may be responsible for the synchronisation of adults emerging (Blackshaw, 1991).

Tipula oleracea has two adult flight periods per year. One in August/September and a second in May/June, although adults may also be present all summer (Blackshaw, 1991). Mating takes place after the eggs have fully developed and not immediately on emergence. The females are multivoltine so egg laying is spread over a longer period than other species. They also fly much further distances and so populations do not build up in affected areas.

Up to 400 eggs are laid with 6 or less eggs being laid at one spot (Dawson, 1932). Eggs are dark brown and are laid into the soil at the base of grass stems (Drury, 1993). Eggs hatch around 14 days later and larvae start to feed (Dawson, 1932). Leatherjackets feed on roots but can often be found on the surface on damp evenings feeding on leaves (Potter, 1998). The leatherjackets are grey/brown to green/grey in colour, legless maggots with no distinct head capsule (Anon, 1984). The first stage larvae are around 0.3cm long (Dawson, 1932) growing to 1cm after approximately one month (around November in the UK) and reaching 2.5 - 4cm after the feeding period in spring (Anon, 1984). Larvae then move down the soil profile in the summer to pupate. The pupae wriggle up the soil profile with the help of backward pointing spines and push themselves partly above the surface for the adult to emerge (Anon, 1984; Potter, 1998).

Problems of leatherjackets on golf turf

Leatherjackets feed on roots and organic matter below the soil surface. They may also come to the surface on damp evenings and feed on leaf material. Damage can range from no visible symptoms to complete sward destruction. Most turfgrass will harbour a low number of leatherjackets and show no adverse effects. The amount of damage is related to the number of leatherjackets present and the condition of the grass (Blackshaw, 1991). In turf, a threshold of 16 leatherjackets m2 has been proposed for insecticidal application (Anon, 1983). Potter (1998) reported more than 1000 leatherjackets m2 on heavily infected turf. Turfgrass that is already under stress will be more severely damaged by leatherjackets. Shallow rooted grass plants find it more difficult to recover from attack (Blackshaw, 1991). During the winter months when turf is only growing slowly (or not at all) leatherjackets may still be actively feeding. Turf may have difficulty in recovering in a period when growth is low or has ceased (Blackshaw, 1991).

As well as feeding on the turf, leatherjackets disrupt the surface of fine turf by tunnelling. This may affect the trueness of the golf green. The activity of birds searching for the grubs also disrupts the turf surface with tufts of grass left loose and holes opened up in the sward. Badgers may also cause damage to the turf surface searching for leatherjackets.

Past chemical control measures

Dawson (1932) lists naphthalene, Jeyes fluid and orthodichlorobenzene as leatherjacket expellants. However, naphthalene gave inconsistent results and orthodichlorobenzene temporarily discoloured the sward surface. Lead arsenate was shown to be an effective leatherjacket killer which removed the need to dispose of the expelled larvae (Dawson, 1932).

Many other insecticides have been shown to be effective in controlling leatherjackets. These included DDT, aldrin, gamma-HCH, gamma-HCH + thiophanate-methyl, triazophos and cypermethrin (Atrick, 1994). Applications of chlordane for earthworm control would also have controlled leatherjackets. The literature often suggested that leatherjackets were only a problem on golf fairways and not on greens. However, since chlordane was banned in 1992, leatherjackets may have become an increasing problem on greens. Leatherjackets were indicated as being as widespread as earthworms on greens, with 81% of respondents indicating leatherjackets being present, in a survey of golf courses in the UK and Ireland (Mann, 2003).

Present chemical control measures

Carbaryl and chlorpyrifos are effective and are still available in some countries for insect control.

Cultural control measures

All methods will be best aimed to reduce the leatherjacket population in the autumn before they spend the winter feeding. Methods that try to reduce the population in spring will not prevent feeding damage occurring. However, it may reduce the population for the successive season (especially in the case of T. paludosa as the females do not move far from where they emerge before laying eggs).

Leatherjackets, especially small ones are susceptible to drought (Anon, 1984). Therefore improving the drainage to prevent excessive moistness during the period of egg laying and hatching will help to reduce the population. Moisture shortage in September and October has been cited as the reason for reduced leatherjacket numbers in autumn (Blackshaw, 1991). However, a difference in leatherjacket numbers found between four different drainage systems could not be related to soil moisture.

The leatherjacket population have been shown to decline over the winter months. This reduction will depend on how severe the winter is. An average decline, in grassland, of 35% with a maximum of 63% has been recorded (Blackshaw, 1991).

In small areas the use of tarpaulins to encourage the leatherjackets to come to the surface has been successful (Dawson, 1932). The leatherjackets could then be swept up and removed. However, the amount of tarpaulin and man hours that would be required over a golf course would make this method prohibitive. Although, in extreme cases this may be possible on greens.

Rolling is often suggested as a method of crushing the larvae. However, there is no evidence to suggest this reduces larval numbers. Rolling during the summer months has reduced adult numbers by trapping the pupae under a soil cap (Blackshaw, 1991). This could have serious implications for other characteristics of the rootzone such as drainage rates.

Biological control measures

Blackshaw (1991) reports little success with naturally occurring enemies of leatherjackets. Tipula Irridescent Virus has been found in a small proportion of the population. It appeared to be transmitted by cannibalism which restricted its spread. Although there was some success by introducing it through treated bran. However, in field populations the leatherjackets must encounter the bran while it is viable which may prove difficult. Wide scale production of this virus would also be difficult as it cannot be produced in vitro (Blackshaw, 1991).

A parasitic wasp (genus Anaphes) has been found in Northern Ireland that was recovered from eggs, which may prove useful in future control methods (Blackshaw, 1991). However, the wasp has not been found in other areas of the UK and may not occur in other parts of Europe or the USA.

An entomopathogenic nematode (Steinernema feltiae) has shown promise in reducing leatherjacket numbers (Peters & Ehlers, 1994). The highest mortality (51%) of leatherjackets was shown to be just before the first molt (15 day old larvae) in a laboratory test. Mortality then declined as the leatherjackets move through the larval stages. The number of dauer juveniles (the life stage of the nematode that infects the leatherjackets) required to kill the leatherjackets also differed depending on the age of the leatherjacket. The lowest LC50 was 7 dauer juveniles when the larvae were 6 days old increasing to 56 when the larvae were 72 days old. However, these results were for leatherjackets placed in sand filled petri dishes and the nematodes applied close to hand. A field trial would be required to determine the efficacy of nematodes in vivo when the leatherjackets may not be close to the site of application.

In the UK, this nematode is currently on the market, aimed at lawn owners. We are unaware of anyone who has used this product and so do not have any information on its effectiveness.

Bacillus thuringiensis var. israelensis (Bti) has also been suggested as a promising biological control agent (Evans, 1996). Autumn application of Bti to grassland in Scotland reduced the leatherjacket population from 3 million larvae ha-1 to 0.5 million larvae ha-1. This reduction was similar to chlorpyrifos applied at the recommended rate. However, spring application of Bti did not significantly reduce the leatherjacket population compared to the untreated control. Chlorpyrifos significantly reduced the leatherjacket population in the spring. In grassland, it is commonly accepted that the economic threshold for treating leatherjackets to prevent a decrease in yield is 1.0 million ha-1 (100 leatherjackets m2). Treatment with Bti in autumn brought the leatherjacket population below this threshold. However, in managed amenity turf the threshold for pesticide application is 16 leatherjackets m2. Further work would be required with Bti to ensure it could reduce the population to an acceptable level for golf.

Grass species infected with endophytes are often less susceptible to insect feeding due to their alkaloid content. Lewis & Vaughan (1997) investigated the effect of endophytes on the feeding behaviour of leatherjackets. Three perennial ryegrass varieties with and without endophyte infections were fed to leatherjackets in a laboratory experiment. There was no significant effect of endophyte infected ryegrass compared to no endophyte infection on weight, survival or number of adults that emerged. It was concluded that the levels of alkaloids may not have been sufficient enough to deter feeding by leatherjackets. The level of alkaloids produced differed depending on the endophyte/plant genotype and the season. It is possible that other grasses infected with endophytes may produce improved resistance to leatherjacket feeding.

References
Anon. (1983). Pests of Turf. Sports Turf Bulletin 140, 7-8.
Anon. (1984). Leatherjackets. Ministry of Agriculture, Fisheries and Food Leaflet 179. pp 8.
Atrick, G. (1994). Insecticides: an historical perspective. Groundsman 47 (1), 34.
Blackshaw, R. P. (1991). Leatherjackets in grassland. Proceedings of the British GrasslandSociety Conference. Strategies for Weed, Disease and Pest Control in Grasland, 6.1-6.12.
Dawson, R. B. (1932). Leather jackets. Journal of the Board of Greenkeepers Research 2, 183-195.
Drury, S. (1993). Worst of Pests. Turf Management May, 16-17.
Edwards, C. A. & Bohlen, P. J. (1996). Biology and Ecology of Earthworms. Chapman & Hall, London, pp 426.
Evans, K. A. (1996). The control of leatherjackets in grassland using Bacillus thuringiensis. Proceedings Crop Protection in Northern Britain, 231-236.
Lewis, G.C. & Vaughan, B. (1997). Evaluation of a fungal endophyte (Neotyphodium lolii) for control of leatherjackets (Tipula spp.) in perennial ryegrass. Annals Applied Biology 130 (supplement), 24-35.
Mann, R. L. (2003). A survey to determine the spread and severity of pests and diseases on golf greens in the UK and Ireland. Journal of Turfgrass and Sports Surface Science, in press
Peters, A. & Ehlers, R. U. (1994). Susceptibility of leatherjackets (Tipula paludosa and Tipula oleracea; Tipulidae; Nematocera) to the entomophthogenic nematode Steinernema feltiae. Journal of Invertebrate Pathology 63, 163-171.
Potter, D. A. (1998). Destructive Turfgrass Insects. Biology, Diagnosis and Control. Ann Arbor Press, Inc. Michigan, 117-118.