Leatherjackets in your turf – Don’t panic

With the daddy long-legs (Tipula paludosa) having laid their eggs over the summer time, the eggs will now have hatched, having then turned into larvae, and will be readily eating away at the base of grasses and grass roots.

Daddy long-legs

Daddy long-legs (Source: Wikipedia )

They can be active at temperatures as low as 5°C (Blackshaw, 1992) and so can continue to feed during periods of mild weather in winter. They become more active and feed voraciously in the spring when the soil begins to warm. When fully grown they reach approximately 3-4 cm in length and then stay within their burrows for about 6-8 weeks before making their way to the soil surface to pupate. They remain as pupae for approximately 2 weeks. In total the larvae spend a minimum of 9 months in the soil.” (Tipula paludosa (European crane fly) https://www.cabi.org/isc/datasheet/54013)

Leatherjacket larva

Leatherjacket larva

So, if you have leatherjackets in your lawn or turf you are pretty much stuck with them, especially as there are now no pesticides which are currently approved for use in their control. (Pesticides Safety Directorate https://secure.pesticides.gov.uk/pestreg/).

You can try nematodes as a biological control (Nemasys Leatherjacket Killer), however, the window of opportunity is very limited as this needs to be applied when soil temperatures are above 12C, so this is generally appropriate to use from August (when eggs are being laid) through to October time, prior to cooling soil temperatures. For a small lawn the cost might be around £20 for a small pack, but for a golf green of 500m2 this is going to cost about £80, so for all 18-greens this will be £1,440, or for a football pitch of some 6,000m2 it will be about £960, so not an inconsiderable sum for one application, with uncertain outcomes as well.

How might you be able to reduce the damage done by these pests? Basically, it’s down to good working cultural and applied physical working (i.e. how effective you use equipment and machinery) practices.

All pests need to feed and if you have a well developed and resilient root system then there is a good chance that your lawn and turf surface will survive relatively intact, albeit with some blemishes, ready for strong growth to recover in spring time. This is assuming that there isn’t a rare overwhelming invasion of them in which case bye-bye lawn and turf surface.

Shallow rooted grass plants find it more difficult to recover from attack” (Mann, 2004); so the emphasis is really to make sure that good groundsmanship helps to deliver a well developed rooting system and not to focus a disproportionate amount of effort into creating a visually pleasing surface to satisfy ‘Joe public’, but which basically lacks substance.

The reason being that if there is enough food – in the form of root biomass – under your lawn and turf surface to help feed the pests (not that we really want to encourage them but we do want to mitigate any damage caused) then you won’t end up with a bare easily pulled up lawn and turf surface because you have enough roots present to resist some of the damage being caused by these pests.

Surely this can’t be right though, and how do the figures stack up?

One leatherjacket grub might eat say 3 grams over its life in the soil (Lam, 1970), but how much root biomass can a turf provide?

Some general data

  • For a very well maintained turf surface, with a good root system, this might have a root biomass of has of 1000g per m2;
  • For a less well maintained turf surface with relatively shallow rooting and which, for example, is mown irregularly and often shaved where a lot more than 33% – 50% of leaf is removed at each mowing, inappropriately aerated, inappropriate fertiliser programme, etc, might have a root biomass of 150g/m2.

(Journal of the STRI (1984) – source used to generalise the root biomass data for this article)

At what level do leatherjackets become a significant problem to turfgrass surfaces?

This is clearly going to depend, amongst other things, upon the quantity of root biomass. If for example, a minimum root biomass of 100g/m2 is required for a basic turfgrass surface then we can see that in the above examples the following number of leatherjackets could theoretically be tolerated:

  • very well maintained surface: 900g / 3g per leatherjacket = 300 leatherjackets per m2;
  • less well maintained turf: 50g / 3g per leatherjacket = 17 leatherjackets per m2;

With a high number of leatherjackets though this is going to attract birds which will peck at the turf for the grubs, so that will introduce another problem.

For some agricultural crops a figure of 50 per m2 has been proposed, however, “These thresholds are much lower than the equivalent for grassland because plant density is so much lower in a cereal crop than in a ley or grassland.” (Dewar et al, 2016)

By contrast for sports turf 15 leatherjackets per m2 has been indicated as a potential threshold for insecticide control (Mann, 2004) (although no pesticides – 2017 – currently approved for this), with up to 1,000/m2 being quoted as “heavily infected turf” (that is a lot), so any specific level at which they may need to be controlled or start to cause a problem will depend upon a number of variable factors. Whatever is decided upon it is clear that ensuring a good root biomass is present will certainly be beneficial and reduce the impact of leatherjacket damage.

Autumn and winter can be a good time for roots to grow and develop so helping to keep the rootzone well aerated is an essential task which should not be neglected. With the wide range of equipment and machinery available there really isn’t any excuse not to carry this out on a regular basis (soil conditions permitting). This type of activity, when carried out appropriately is an integral part of any Integrated Pest Management plan (or integrated turf management plan, as called by some).

Taking a very wide ranging systematic approach to pest control can really help to reduce the pesticide load on the environment and help to ease back on the industrial level of applications and pollution we have been doing over the years, often without thinking of sensible, effective and quite reasonable alternatives because of the persuasive and often disingenuous arguments from the manufacturers and suppliers of expensive pesticides  – but that’s a story for another day as they say: This isn’t to say there isn’t the need for selective, well targeted applications, but only in specific cases where it’s fully justified and genuinely good groundsmanship, not lip service, has been effectively demonstrated.

Note: All the above data have been generalised to help illustrate that good cultural and physical practices can significantly help to reduce damage and annoyance from leatherjackets – Oh, if only the same could be said for interfering users of sports surfaces!

References

Ruth Mann, (2004), ‘Review: To identify, collate and assess research on the management and control of the main pests and diseases on European golf courses’, R&A / STRI, p.11

Andrew Bon-Quoc Lam (1970),’ Effect of some nematodes and microorganisms on the leatherjacket, Tipula paludosa Meig. larvae, and their potential use as biological control agents’, Thesis, Simon Fraser University. N.B. I’ve generalised a range of data to give an indicative figure for this article only

Canaway, P.M. (1984) ‘The response of Lolium perenne (perennial ryegrass) turf grown on sand and soil to fertiliser nitrogen II. Above ground biomass, tiller numbers and root mass’, in The Journal of the Sports Turf Research Institute, Vol. 60, pp19-26

Parr, T.W., Cox, R. & Plant R.A. (1984) ‘The effects of cutting height on root distribution and water use of ryegrass (Lolium perenne L. S23) turf’, in The Journal of the Sports Turf Research Institute, Vol. 60, pp45-53

Alan M. Dewar, Andrew Ferguson, Judith K. Pell, Caroline Nicholls and Jenna Watts, (2016) Research Review No. 86. ‘A review of pest management in cereals and oilseed rape in the UK’, Agriculture and Horticulture Development Board, p.82

Chris Gray, 30th November 2017