Autumn timing to target leatherjacket control
Leatherjackets continue to cause extreme levels of damage on afflicted golf courses, with effects on surface smoothness and ball roll, as well as huge impact on turf health from larvae feeding on roots and stem base.
And this season there’s the added pressure of effects on turf already weakened by the prolonged extreme heat and drought across the majority of England, writes Syngenta Technical Manager, Pete May.
The conditions pose an additional dilemma in deciding on control strategies for this autumn's control programme. Under label restrictions for Acelepryn insecticide, greenkeepers are only permitted to treat 10% of the golf course area in any one season.
For most that typically covers the greens, tees and areas identified at most risk from effects – possibly alongside woodland or where there has been historical damage from birds or badger digging in search of larvae, for example.
While the premium playing surfaces will always be the priority, this year fairways and approaches may be especially hard hit by leatherjacket activity if the turf is particularly weak without irrigation. That could be further compounded if unirrigated soils remain dry, where the potential for control using NemaTrident beneficial nematodes could be compromised. Nematodes require a persistently high level of soil moisture to survive and move to seek out larvae.
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Leatherjacket larvae are most active in moist soils, where they can be effectively targeted for control. But if conditions are too dry, they will move down the soil profile and only return to the surface to feed. That could limit the amount of time they come into contact with an Acelepryn insecticide treatment or beneficial nematodes, with potential effect on results.
Research compiling years of data recorded by Syngenta Pest Tracker monitoring of adult crane fly activity - signifying egg laying that will result in leatherjacket larvae – consistently indicates the optimum timing for Acelepryn application on or around the 20th October each year, followed by a NemaTrident F beneficial nematode application within the next seven days.
Ideally, soil moisture should be around 20% for Acelepryn application and 30% at the time of a nematode application - then held at 25%+ for a week to 10 days, if possible, to maximise activity. Wetting agent programmes could provide a valuable aid in maintaining moisture in the target root zone.
The aim is to have the maximum number of leatherjackets active in the upper soil zone when the concentration of Acelepryn is at its greatest and nematode numbers at their highest.
Treatment sequence
On courses with a very low threshold for damage, or where heavy infestations have previously caused severe losses, it can be a sensible approach to bolster the Acelepryn treatment with a sequence of NemaTrident nematodes, to enhance overall control rates and consistency.
The importance of soil moisture will, in part, dictate the leatherjacket strategy and timing for different areas of the golf course or sports facility. It will largely depend on irrigation availability - both the infrastructure and water resources later in the season - and how that fits with playability schedules for maintaining elevated soil moisture.
Leatherjackets tend to target the same areas of turf repeatedly. That’s because the conditions in some areas particularly favour their life cycle, and the pests are relatively mobile – so they will often recolonise areas that may have previously been successfully treated. Larvae will readily migrate from areas of longer grass in surrounds or out of play areas where eggs may have been laid, onto irrigated greens and attracted by moist soils.
Application advice
As with all applications for soil target the best use guidelines for treatments advocate mowing prior to application, to limit spray retention on the leaf. Spray water volume should ideally be at 1000 l/ha, applied through 08 XC Soil Nozzles, with coarse water droplets helping to move as much product as possible to the soil surface. Furthermore, the larger orifice 08 nozzles are essential to minimise risk of damage to nematodes during application.
Application with a forecast of light rain or heavy dew to wet the leaf surface is also preferable, or to irrigate as soon as possible after treatment.
Changing weather patterns have made managing treatment programmes more challenging to coincide with wetter periods on areas without irrigation, particularly in extended dry periods of later summer and early autumn. In most seasons, nematodes are not a viable option on unirrigated surfaces.
Waiting for seasonal rains later in the autumn could be compromised by falling soil temperatures, which should be consistently above 8⁰C for nematodes to work efficiently. It’s also worth noting that nematode applications are best made either first thing in the morning or in the evening, to avoid peaks in UV light that can affect performance.
Syngenta leatherjacket research in a high-pressure situation, with 100 larvae per m2 in the untreated turf areas, showed 89% control from Acelepryn alone, compared to a 65% reduction in larvae population using just NemaTrident F plus NemaSpreader. However, where the two components were used in sequence, the trial resulted in complete larvae control.
Alongside physical control of leatherjacket larvae with Acelepryn and NemaTrident nematodes, Syngenta turf health programmes - including Comprevo and Vyplenza biostimulants, Primo Maxx II PGR and Qualibra wetting agent – are designed to enhance rooting and vigour. That will be especially important this season to make plants more resilient to pest damage, as well as recover faster.
Aeration strategy
Syngenta research by the STRI has shown that aeration practices can also affect the efficacy of controls. Punching big hollow-tine holes through the surface provides channels for leatherjackets to move up to the surface to feed at night, and return deeper in the profile by day without coming into contact with the treatments. Results showed leatherjacket numbers were controlled two to three times better where no aeration took place, compared to hollow-tine; with a less aggressive slit tine having a limited negative effect.
The implication is that, where practicable with maintenance schedules, major aeration works should be undertaken outside of the leatherjacket control window – especially on areas where larvae control is a priority.
