Black beetle numbers on the rise

Black Beetle

AgResearch scientists warn that one more mild winter could result in a population explosion of black beetle.

“Recent AgResearch trial work shows that black beetle populations are on the increase and development is more advanced in autumn 2014 than in the previous five years,” says AgResearch Science Team Leader Biocontrol and Biosecurity Dr Alison Popay.

​“This means that the adult black beetles will have plenty of time to feed and build up fat reserves to help them through the winter.  If warm conditions continue through autumn and spring conditions are right, some farmers could be facing another serious black beetle outbreak next summer.”

A black beetle field day was recently held on the Taupiri farm of Martin Henton. Martin is part of the Waikato Black Beetle Action Group who obtained Sustainable Farming Fund investment for the project “Beating black beetle: developing pest-resistant dairy pastures in the Waikato.” His property was hit very hard in the last black beetle outbreak in 2007-2010 and since then the pest has persisted at higher levels than on many other farms. Because of this AgResearch, the research partner in the Sustainable Farming Fund project, has used Martin’s farm for a number of project trials.

AgResearch scientist Dr Kumar Vetharanium has used the trial data and that available from the severe outbreak in the 1980s to build a model that should give farmers more advance warning of outbreaks.

“The model predicts that if it’s warm and dry again in the next spring-summer period, we will be heading for trouble and there would be huge problems if this continued into 2016,” says Dr Popay.

“NIWA is predicting about 50% chance of an El Niño event July – Sept. While Waikato farmers may not like the cold wet conditions it may bring, it should help reduce overwintering black beetle adult populations.”

Dr Popay says that farmers can make decisions now that will prepare their farm for the likely black beetle outbreak if winter is warmer and drier than average.

“When renovating this autumn, use a black beetle-active endophyte and manage pastures to ensure no gaps develop where beetle-friendly paspalum and summer grasses can establish. Establish endophyte pasture now to ensure it will be robust enough next summer when pressure from the black beetle increases.

“Legumes are not attacked by black beetle. Also consider crops like chicory, which are not a good host for black beetle and can help break the pests’ lifecycle.”

Dr Popay warns that endophytes in grasses will be of little use in breaking the life cycle of black beetle if an alternative feed source such as C4 grasses (especially paspalum), Poa annua, other grass weeds or endophyte-free ryegrass, including annuals and Italian ryegrass, are available.

“These alternative feed sources will only add fuel to the fire as it provides the perfect environment for the pest,” she says.

One trial on Martin Henton’s and fellow action group member Stu King’s properties is investigating the possible benefits of liming in reducing black beetle populations.

“It is too early to give definitive recommendations from the lime trial other than to say low soil pH appears to favour black beetle and getting soil pH into the optimum range for your soil type will help pasture production and quality,” says Dr Popay.

She advises farmers looking for more information to contact their local DairyNZ Consulting Officer.

“They will be able to discuss the range of options available to you.”

DairyNZ also has a black beetle Farmfact available on www.dairynz.co.nz. Further information about the black beetle can be found at pestweb.co.nz, the directory of New Zealand’s most damaging pests and weeds. Farmers can also sign up to receive management and control advice specific to their region through the AgPest (formally Pestweb) Pest Alerts.

About the Black Beetle

Black beetle is an African species but has been present in New Zealand for several decades. At the limit of its climatic tolerance, its distribution is restricted to Waikato and Bay of Plenty northwards with a southward coastal extension into northern Taranaki and Hawkes Bay. Black beetle outbreaks occur sporadically and follow above average spring temperatures. It has a high temperature requirement for most life processes. Female longevity, number of eggs produced, egg viability, larval survival, growth rate and the amount they eat are all favoured by temperatures greater than 20°C and are severely inhibited at between 10-15°C.

Adult beetles are a characteristic glossy black and about 15 mm long with females being larger than males. They are usually found in the top 1 cm of soil. They undergo extensive dispersal flights in spring and autumn but surface air temperatures must be above 17°C for flights to occur. The eggs, about 2mm long and ovoid to spherical in shape, are laid singly in soil, close to the surface, in spring.

Both beetles and larvae damage pasture, other agricultural and some horticultural crops. Larvae cause damage to pasture in summer and adult beetles cause damage in autumn and spring.