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Fall armyworm update 10 March 2023

Key points:

  • The insecticide Sparta™ is now on label for both aerial and ground applications for the control of fall armyworm on maize and sweetcorn crops. Consult with your advisor.
  • Avoid the use of insecticides that are ineffective on fall armyworm and potentially harmful to beneficial insects.
  • The total number of finds for the 2022-23 season has now reached 128, an increase of only one find. This could indicate a slowing of its spread at this stage of the season.
  • Only four fall armyworm moths were found in traps in Northland this week; low numbers of larvae of varying sizes have also been found in the region.
  • The main concern has been the wet condition of many crops, hence scouting and reporting may not be thorough, which is fully understandable.
  • Many crops have been or are close to harvest around the country, which means the fall armyworms preferred food source is reduced. Therefore, it is important to stay vigilant and scout neighbouring paddocks, as fall armyworm could look to other crops for a food source in the absence of maize and sweetcorn.
  • There continue to be reports of fall armyworm larvae being parasitised by the parasitic wasp Cotesia sp. which will help contain the numbers.
  • We have received questions on thresholds for economic damage. While we work on New Zealand specific information, international (Australian) guidelines suggest, that at whorl stage and above, economic damage will occur when at least 20% of plants have larvae present and/or signs of damage on 75% of plants. Scout crops (if safe) by using a “W” pattern; fall armyworm tends to feed along rows.
  • We are still in a response. All finds must be reported to MPI here or call 0800 80 99 66
  • There are no negative consequences to growers for reporting, as this pest will not be controlled by removing crops.

Photo: Fall armyworm pupa.

If there is significant damage on plants and cobs but no worm is present, they may have pupated. Gentle scraping of the soil surface around the plant base may reveal the pupa burrow. They may be at varying depths of up to 10cm.

Thresholds of economic damage:

For the latest identification guides click here and MPI Website here, or contact Ivan Lawrie or Ash Mills

For other useful tools and guides on detection and identification, consult the FAR website.