Turf damage caused by black beetle larvae or adults can be minimised by preventative action taken early in the season.

Black beetle (Heteronchus arator) can be a challenging problem on turf and was particularly severe during the summers of 2009 – 2012. Few sports were spared, with damage being reported on golf, bowls, sports fields, race tracks and croquet lawns.

Adult black beetle.

Black beetle is a native of South Africa
and is found in the warmer parts of New Zealand, namely:

• On the west coast, from Wanganui north
• On the east coast, north of Hastings
• Inland, north of the South Waikato

Typically black beetle prefers lighter sandy or loamy type (volcanic) soils with good drainage. Creeping, thatch-forming grasses (such as browntop, couch, kikuyu or paspalum with its fleshy stems) are a favourite. Although not a creeping grass, Poa annua is also susceptible.

Life Cycle and Description

The life cycle of black beetle is summarised in Table 1.

Black beetle damage – moderate damage/thinning.

Black beetle has one life cycle per year. Typically numbers and hence damage are highest in the year following a hot, dry summer. This is the reason why black beetle was so damaging in the last three summers but is expected to be less of a problem this coming year, given that last summer was cooler and wetter than usual. Adults progressively emerge as soil temperatures warm, typically from mid-August onwards.

The larvae passes through three instars with the first instar usually being seen mid-late December. In some situations damage can be confused with that caused by grass grub (Costelytra zealandica). Generally grass grub larvae (first instar) become evident from February onwards and, as such, will be smaller than black beetle larvae. However, the most obvious distinguishing feature between the species is that black beetle larvae have orange spiracles down their side.

Damage to Turf

Both larvae and adults are damaging to turf. The main damage (shortened roots and the subsequent ‘peeling turf’) is typically seen from late January onwards and can occur until the autumn rains in March/early April. Damage is worst on unirrigated turf and, in particular, where endophyte-free cool season grasses predominate.

Traditionally damage from the adult has been underestimated or not considered at all. However in autumn, particularly on unirrigated turf, adults can be very damaging to the grass recovering from the summer drought, resulting in significant thinning of the turf cover.

Additionally, the burrowing activity by adults and/or subsequent feeding activity by birds can be damaging to fine turf surfaces such as on golf or bowling greens.

Black beetle damage – severe damage/loss of cover.

The key to managing black beetle is to control the emerging overwintering adults, before they lay down the next generation.

Predicting a Black Beetle Problem

Monitoring is recommended where you have had a history of issues with black beetle or where, in the previous autumn, there were either large flights of or significant burrowing activity by the adult.

To determine whether black beetle is likely to be damaging turf during the coming summer:

1. Take 10 random spade divots across a sportsfield or fairway and count the number of adults in each divot.
2. Calculate the average number of adults present in a divot and multiply by 30 to get the approximate number of adults present/m².
3. Multiplying the average number of adults/m² by 3 will give an approximate number of larvae that could be present in the coming summer. Indicative threshold numbers where damage to turf is likely is summarised in Table 2.

Note: With fine turf surfaces such as greens, it is recommended to use a pyrethrum drench to flush the adults to the surface. Total numbers can then be estimated.

Control Options

Endophyte

Where ryegrass is sown, the selection of a high endophyte cultivar offers one of the best strategies for preventative control of black beetle. These endophyte fungi produce toxins that deter the black beetles from feeding (but not AR1 endophyte). The endophytes do not directly affect the larvae.

Chemical control

For non-endophyte grasses, chemical control will likely be required on occasions. When developing a suitable programme, you need to be very clear about the life cycle stage you are attacking and that conditions are suitable for the control programme to work.

Emerging adults

The preferred approach when chemically controlling black beetle is to target the emerging overwintering adults and thereby prevent or at least lower the number of larvae that then occur during summer. The key to being successful is to appreciate that the adults emerge progressively over several months (late August – November) and consequently you will require either:

• Repeat applications of a short-lasting ingested or contact insecticide.
• Long-lasting contact or ingested insecticide.

Potential options are summarised in Table 3.

Larvae

For larvae, a soil active insecticide is required. The challenge during a dry summer and on unirrigated situations (where damage is typically more severe) is getting the chemical down to where the grubs are active. Key issues include applying sufficient water to wash the chemical into the profile and secondly, being aware of the effect of organic matter which can lock up many insecticides.

Summary

Black beetle can be a problematic pest on turf, particularly on non-irrigated situations. The key is to assess numbers in spring and control the emerging overwintering adults before they lay down the next generation.

Cast left on surface from burrowing beetle (adult).

® Registered in NZ for black beetle.
NR Not presently registered for black beetle.

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