Black beetle battle rages on

CHRIS GARDNER
Last updated 13:37 12/04/2013
A South African black beetle
FAIRFAX NZ

A South African black beetle.

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AgResearch is developing a new weapon in the war against pasture-damaging South African black beetle.

Hamilton-based pasture scientist Warren King is one of the brains behind the fight against the South African black beetle, an arrival in the 1940s, which is causing increasing damage to northern North Island pastures.

The pasture damage means farmers cannot feed their cows and the cows cannot produce milk. Then there's the cost of replacing the pastures.

The larvae cannot be treated with insecticide since the chemicals would find their way into grazing cows and then milk.

A string of very dry summers and autumns has contributed to higher black beetle numbers, especially on lighter soil types such as ash and peat. As many as 95 black beetles per square metre have been seen. Thirty or more is typical, but any more than 20 is a concern.

"We are trying to develop new tools," King said.

"What we are trying to do is look at developing some bio control agents and we have got some candidates. We are talking about a bacterium that's very effective against black beetle in the lab, but I don't wish to give farmers any sense of hope that there's a silver bullet coming."

King said it could be between two and five years before the work reached the market, and it could fail before then.

"We have proof of concept and function but the trick is getting it to work cost effectively in the field," he said.

The results of AgResearch's latest South African black beetle survey are in and puzzling the scientist.

King, who has been studying black beetle populations in the Waikato and Bay of Plenty since the 2007/08 drought, found black beetle levels remaining at alarming levels in some paddocks, while completely disappearing from others.

"It's puzzling," he said.

Four out of the 24 Waikato paddocks monitored this season had more than 20 black beetles per square metre, the level at which King is concerned, with one of three of Gordonton dairy farmer Martin Henton's monitored paddocks delivering a reading of 28. There were no black beetles present in 10 of those paddocks.

Black beetle larvae have cost the Hentons $180,000 in lost milk production which dropped 20 per cent as a result of the incursion.

"It's starting to be worrying . . . It's incredible how much damage something this little can do."

In the Bay of Plenty only one of 13 monitored paddocks registered 20 black beetles, with four registering none at all.

"We have got a lot of zeros in there that are brilliant," he said. "We go into the paddock with a spade, dig a hole and pull the soil apart by hand. We do that 10 times across the paddock and multiply that up to get a per square metre number."

"They are certainly not the highest numbers we have seen across the region, but the fact that we have got damaging numbers is a concern. The fact that they haven't dropped away on some farms means that pastures are under constant pressure."

King is expecting next season's numbers to be "calamitous" because of the drought.

"We don't fully understand the cycling of black beetle but these dry conditions seem to set us up for an outbreak in the next season. There's already some black beetle in the system, but we might be facing a really bad year next year.

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"For many farmers the opportunity they have got to establish a good strong pasture is now with a novel endophyte. They should be concentrating on making their pastures black beetle resistant with NEA2 and AR37 - those two are the most commonly recommended. They are available from all rural retailers."

King said farmers could now rely on the information from the retailers.

"Three or four years ago there were some mistakes made. Some of the advertising material put out by companies like RD1 were way off the mark.

"We are all now working much more closely. When you compare the level of knowledge in those rural retailers they have really focused on it and are really clued up."

- Waikato Times

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