Fall armyworm marches on
A large population of fall armyworm, which was first discovered in New Zealand in 2022, could completely destroy a maize crop if the conditions were right.
And the Foundation for Arable Research (FAR) says there have been 110 confirmed reports of the insect’s presence in the 2023/24 growing season.
FAR biosecurity officer Ash Mills said this was the second season the worm had been present in New Zealand, and last year’s weather events led to late planting, which made crops vulnerable.
“The fall armyworm incursion started off in Northland at the very beginning of November 2022. By the end of the season, it was across the country.”
Mills said pheromone traps could show evidence of adult moths but crop scouting when the plants first emerge was the most effective way to detect the worm.
“Identifying egg masses on the underside of leaves or small larvae is key to control if the pest population is above recommended thresholds. The younger the crop and younger the larvae, the better chance of successful control.”
Mills said insecticides such as synthetic pyrethroids upset the biological balance of the crop. They could be harmful to the parasitoid wasp and other beneficial insects which were a major line of defence, while pest insects built up resistance.
“New Zealand has inherited resistance as fall armyworm and other pest insects have travelled the world and eventually got here.
“We have been recommending Sparta, which contains spinetoram. It is the only insecticide on label which can be used on maize crops.
“If used at the correct time of day when beneficial insects are not present, it reduces the harm. If sprayed at night, it will dry out enough to reduce damage.”
The worst infestation Mills had seen was in Northland this year.
A grower detected fall armyworm so they sprayed with a synthetic pyrethroid. Unfortunately. it killed all the beneficial insects and the remaining pests managed to get through another lifecycle. This led to 100% defoliation; cosmopolitan armyworm stripped all the leaves off the crop.
Unlike other maize pests such as corn earworm, fall armyworm is a tropical pest so its lifecycle slows down as temperatures cool.
Mills hoped its mortality rate this winter would be high.
“As there is generally a lack of maize and sweetcorn, we assume over winter larvae will be in ryegrass or the closest palatable plants.”
Far North farmer Jacob Garton runs sheep and beef, but his main business is Supa Feeds producing animal feed and pet food products. Garton said they were battling fall armyworm before the country realised the havoc it could bring.
“Fall armyworm wiped out a couple of our crops,” Garton explained. “It ate the centre of the plants, resulting in 95% of the crop unable to flower and pollinate, leaving no grain to be harvested.”
Since then, his team had undertaken significant testing and trialling each maize season, from which they have emerged with a plan of attack.
“We are bringing planting dates forward and employing the use of Sparta. Fall armyworm provides an ongoing challenge. but the team continues to believe in keeping it local, personally cultivating, growing and harvesting maize crops around Northland.”
Mills said FAR had a three-year project looking specifically at fall armyworm.
“We are trying to get growers to refrain from using some of the organophosphates and other more damaging insecticides.
‘‘We are trying to liaise with agronomists to work out whether they need to apply a product at all.
“We will be working with other experts in the sector to build integrated pest management strategies specific to maize crops and fall armyworm. As the project develops, we will learn more and in the end have a pretty robust strategy.”
Fall armyworm is thought to have been carried on the wind from Australia, arriving in New Zealand around February 2022, according to the Ministry for Primary Industries website.
The moth is known to be spreading around the world and is present in the Americas, Africa and Asia, as well as parts of Australia.
It is a plant pest that can feed on more than 350 plant species, particularly sweetcorn and maize. Adult fall armyworm moths are strong flyers and will travel hundreds of kilometres on wind. The larvae can also be spread in cut flowers, fruit and vegetables.
After attempting eradication, Biosecurity New Zealand has shifted its focus to longterm management of the pest, as the method of arrival suggested it would recur, MPI’s website reported.