Damage can range from no visible symptoms to complete sward destruction
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
Leatherjackets were indicated as being as widespread as earthworms on greens
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