Warm winter could bring black beetle plague

GERALD PIDDOCK
Last updated 11:01 20/05/2014
Black beetle
Fairfax NZ

BEETLE-MANIA: Farmers urged to prepare now for an outbreak.

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AgResearch scientists warn that another mild winter could result in a population explosion of black beetles on Waikato pastures.

Recent trial work showed that black beetle populations are on the increase and development is more advanced in autumn 2014 than in the previous five years, AgResearch science team leader biocontrol and biosecurity Dr Alison Popay said.

"This meant that the adult black beetles would 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."

Black beetle numbers had surged because of the warmer than normal winter in 2013.

The warmer temperatures lifted the survival rate of the pests, she said.

The pest was more frequent in lighter, free draining soils in Waikato, Bay of Plenty and south to Te Kuiti.

"Bit by bit it's creeping south."

Modelling from data collected from the farm of Taupiri farmer Martin Henton showed farmers could be heading for trouble if the spring-summer period is warm and dry again.

"There would be huge problems if this continued into 2016," Popay said.

"Niwa is predicting about 50 per cent chance of an El Nio event July - September. While Waikato farmers may not like the cold wet conditions it may bring, it should help reduce overwintering black beetle adult populations."

Farmers can make decisions now that will prepare their farm for the likely black beetle outbreak if winter is warmer and drier than average. They had few options apart from using black beetle-active endophytes in autumn regrassing, Popay said.

"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."

Farmers should also consider planting legumes, which were not attacked by the beetle, or crops like chicory, which was not a good black beetle host and could help break the pest's lifecycle.

Popay warns that endophytes in grasses will be of little use in breaking the lifecycle 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 were available.

"These alternative feed sources would only add fuel to the fire as it provides the perfect environment for the pest," Popay said.

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