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Farm advice: Farmers urged to watch for pest fall armyworm

The tropical insect pest was discovered for the first time in the South Island

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Following the discovery of the tropical insect pest with a big appetite for maize and sweetcorn on the West Coast – the first time it has been found in the South Island – farmers and contractors are being urged to keep vigilant out for fall armyworm. 

Before the West Coast detection, confirmed finds of fall armyworm had previously only been in areas it was found last year, including Northland, Waikato, Bay of Plenty, and Taranaki. 

Fall armyworm was first detected in New Zealand in March last year, likely windblown from Australia. As of mid-January, three confirmed finds of fall armyworm were identified on the West Coast, bringing the total number of finds since 1 September 2022 to 56 in New Zealand. This is up 11 on the previous week. A find was confirmed in a paddock of maize near Hokitika, and since then, other finds in the region suggest several maize crops are affected, Foundation for Arable Research general manager of business operations Ivan Lawrie says.    

The industry is working with the Government on the response to the pest, with members of the FAR/Seed and Grain Readiness and Response (SGRR) team along with Dr Scott Hardwick from AgResearch/B3 visiting the Hokitika property to assess crop damage and the efficacy of control.

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Visible damage in the plant whorl and an accumulation of frass (caterpillar faeces) on a maize crop near Hokitika

“We’re very grateful to the grower and local rep for the swift reporting, which raised this important alert,” Ivan says.

All maize growers in the North and South Islands should be inspecting crops regularly. Control is easier and more effective if the damage is identified at the early stages before the fall armyworm larvae move into the plant whorl.

About Fall Armyworm

Fall armyworm larvae feed on more than 350 plant species, especially sweetcorn and maize.

Fall armyworm is the name commonly attributed to the larval stage of the moth Spodoptera frugiperda, which can chew through crops, causing widespread damage. Its life cycle has an egg stage, up to six caterpillar (larval) stages, a pupal stage, and an adult moth stage. Adult fall armyworm moths are strong flyers and will travel hundreds of kilometres on storm fronts.

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Fall armyworm larvae have key identification features including an inverted ‘Y’ marking on the head area and four large spots in a square arrangement on the second to last segment

The maize plants on the Hokitika farm are at the 8–10 leaf stage and the larvae present were large, suggesting that some had already dropped to begin pupation. Well over 25% of plants were affected at the whorl stage, so the grower’s decision to spray was the correct one, based on the threshold guide from international data. The insecticide Sparta (spinetoram 120g/L) is now on label for use on fall armyworm in maize and sweetcorn crops for ground applications.

Corn earworm (Helicoverpa armigera) was also present in the crop. The pests can look similar, so if growers have any doubts, photograph different specimens and send multiple pictures to the Ministry for Primary Industries (MPI).

More than 200 FAW traps deployed by the response group continue to be assessed throughout New Zealand. As this is still an unwanted organism, all findings must be reported to MPI at report.mpi.govt.nz/pest or using the app findapest.nz, by email to FAW@mpi.govt.nz or by freephone 0800 80 99 66.

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Ivan says there are no negative consequences to growers reporting, as crops where the pest is confirmed will not be destroyed or put under controls.

The models indicate that moths should start to be detected this week and the next, so farmers are urged to continue to check traps and report online. Growers and reps should be actively scouting for caterpillars on the crop and not just relying on the moth catches from traps. 

For more information, visit mpi.govt.nz/dmsdocument/50839-Fall-armyworm-fact-sheet

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