Black beetle can ravage pasture in the upper North Island, and a project that arose from ongoing black beetle problems on
many Waikato farms has revealed a practical, effective tool.
The recently completed New Tools to Combat Black Beetle project has found that lime does more than manage soil acidity; it also helps to prevent black beetle outbreaks by reducing larvae populations.
The project involved farmers from the Waikato Black Beetle Action Group and scientists from AgResearch, and was funded by the Sustainable Farming Fund, Ballance Agri- Nutrients, Dairy NZ and Graymont Lime.
Earlier research had found that ryegrass with black beetle active endophytes on northern North Island dairy farms would keep the insects’ numbers down by protecting against adults feeding at the base of the stems.
However, nothing was available to deter black beetle larvae from feeding on roots.
Farms with light or peat soils, on which the insect can thrive, had no effective form of protection against black beetle larvae.
A new tool was needed to combat this.
Involved in the recently completed SFF project was Ballance forage specialist Murray Lane.
“Over time we’ve investigated a number of options. A bacterial bait looks promising but isn’t commercially available yet. Lime stands out as it affects the first instar larvae,” he says.
The project found that applying lime in spring, to maintain pH around 6.0 to 6.2, reduced larval populations by about 30 per
cent, compared to untreated pasture.
The lime continued to be effective over a three year period.
The existing industry recommendation regarding lime application on dairy farms is to target soil pH levels in the range of 5.8 to 6.0.
As a result of the project, a target of pH 6.0 to 6.2 is recommended for farms prone to black beetle outbreaks, based on field and laboratory results.
AgResearch estimates black beetle costs NZ dairy farmers $223 million and sheep and beef farmers $19 million every year.
It affects a million hectares across NZ, mostly in Waikato, Bay of Plenty and Northland, with smaller areas in Taranaki and Hawke’s Bay.