By Alistair Beggs, STRI head of agronomy
Insect pests of fine turf have been problematic in the UK for many years. However, until recently controlling their behaviour, and the subsequent behaviour of birds and mammals feeding on them, has been reasonably straightforward to achieve.
Although there were warnings of likely changes to pesticide legislation in recent years, industry practice continued as normal. It was common for greenkeeping teams to treat prone and valuable areas with insecticides, such as chlorpyriphos and imidacloprid, at the appropriate time of year.
Both products were very effective insecticides. A single application would ordinarily eliminate any problems a greenkeeper was likely to see from grass and root feeding insect grubs for up to twelve months.
However, now both active ingredients have been recently withdrawn from use, in amenity turf, the impact leatherjacket and chafer grubs have on fine turf has been steadily growing.
- Leatherjackets are the grubs/larvae of the crane fly or ‘Daddy long legs’
- Adults emerge in August and September
- Females do not move far from emergence and mating occurs quickly with eggs being laid within 32 hours of emergence
- Up to 400 eggs are laid with six or less eggs being laid at one spot
- Eggs are dark brown and are laid into the soil at the base of grass stems
- Eggs hatch around 14 days later and larvae start to feed
- Leatherjackets feed on roots but can often be found on the surface on damp evenings feeding on leaves
- The leatherjackets are grey/brown to green/grey in colour, legless maggots with no distinct head capsule
- The first stage larvae are around 0.3cm long growing to 1cm after approximately one month (around November in the UK) and reaching 2.5–4cm after the feeding period in spring
- 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
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. In golf turf, a threshold of 16 leatherjackets m2 has been proposed for insecticidal application.
Other factors you should consider include:
- 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
- During the winter, 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
- 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
Chafers or white grubs are the larvae of the chafer beetle, of which there are a number of different types.
- The garden chafer is the most abundant species
- The adult is around 9mm long with brown wing cases and a bottle green head
- The larvae grow to around 18mm
- It has a one-year lifecycle
- Adults are traditionally found in late May or June. However, this depends on spring temperatures
- Adults emerge over a period of approximately 10 days, flying between 10.00am and 12.00am in sunny conditions
- Males may swarm looking for emerging females
- Females mate as soon as they emerge and burrow back into the soil to lay eggs
- The eggs are laid in groups of two to six eggs (a total of 10–50 are laid) about 1 cm below the soil surface. This often results in a localised build-up of the chafer population
- The female then emerges again and feeds on trees and shrubs before flying to another site to lay more eggs
- The eggs hatch four to five weeks later and the larvae begin to feed on roots
- The grubs grow through three instars
- The third instar digs deeper into the soil to hibernate. As no more feeding will occur between hibernation and pupation, garden chafer larvae do not cause grass damage in the spring
- The grubs pupate (pupae can be found in April) and adults emerge the following summer
Cockchafer and summer chafer have two to three-year lifecycles, respectively. Therefore, larvae of these species may cause damage in spring as soil temperatures increase and larvae resume feeding.
Damage to the turf can occur directly as a result of high numbers of grubs feeding on root stock and turf. Or it can come as a result of birds and mammals hunting for the grubs as a food source. It is not difficult to imagine the damage that can be caused to fine turf areas in these circumstances and the images below illustrate some of the turf scenarios seen this spring.
Efforts continue to be made by clubs and their advisors to make the golfing population aware of the changes in product availability and the likely impact this could have on golf course conditioning.
Biological treatments can be effective but the process of optimal application needs to be learned by industry professionals, and this takes time. Other avenues of progress are currently under investigation, such as newer and safer insecticides and trying to make biological control easier to implement, but these developments need to be supported scientifically and financially.
At this moment, the turf industry appears vulnerable and this means that a host venue for a major sporting event could be impacted by an insect based problem. In the worst-case scenario, this could have notable implications for the event concerned and mean that surface quality could be compromised.
STRI is the leading, largest and most experienced professional body working specifically within golf. If you wish to engage one of our advisory team to discuss pest problems, please email firstname.lastname@example.org or call 01274 565 131