Prepare for fall army worm as weather warms
As spring nears and temperatures increase, growers should look out for fall army worm. Ivan Lawrie, general business and operations manager at the Foundation for Arable Research, said he was on a scouting trip in the north of the country last month and had not found any sign of fall army worm in traps that growers had put out.
“That's good news. But we don't want to be complacent, and we want people to be on the lookout,” he said.
In February, Biosecurity New Zealand deputy director-general Stuart Anderson said eggs from the pest were found in Tauranga for the first time in March last year. In December, the larvae was found on 18 farms in the North Island, and by January it had spread to the South Island.
In April, Lawrie said the agriculture pest was unlikely to be wiped out.
Fall army worm has caused devastation in other countries, with the damage in South Africa compared to biblical plagues.
It was estimated that Brazil spent about US$600 million (NZ$1 billion) a year controlling outbreaks.
Lawrie said if the pest emerged he expected to begin seeing evidence of it late this month.
Growers needed to be on the lookout for caterpillars in the early stages of the crop, he said.
Early monitoring of crops was needed in milder regions such as Northland, Auckland and Waikato, where the tropical pest may overwinter.
Lawrie said in a Foundation for Arable Research newsletter that “fall army worm can attack crops at all stages, but its control is much more effective when larvae are
Treatment is best between maize plant emergence and growth stage V6, before larvae can hide in the whorl.
small and are feeding on leaves’’.
“Treatment is best between maize plant emergence and growth stage V6, before larvae can hide in the whorl.
“Application of an insecticide is only economic for maize if more than 20% of the plants have significant foliar damage. Application is more effective on fall army worm up to the third larvae instar as they are more prone on the plant’s foliage and have not yet become entrenched.
“International literature says you only need to hit it once. The key is to get it early.
“Fall army worm is less of a problem for silage growers and more of a problem for maize grain growers and particularly sweetcorn producers,” he said.
Growers were advised to avoid the use of insecticides that were ineffective on fall army worm and potentially harmful to beneficial insects, such as the parasitic wasp,which appeared to be having an impact on fall army worm populations.
Fall army worm had no dormant period and needed a food source to overwinter in frost-free regions.
“Anything that is green will enable it to overwinter, and it has been observed on ryegrass and clover in a harvested maize paddock, as well as volunteer maize.”■