Fall armyworm has been identified in South Island maize crops, taking the total number of finds since 1 September 2022 to 56.
There have been three confirmed finds of fall armyworm on the West Coast of the South Island.
Early this 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.
Members of the FAR/SGRR team along with Dr Scott Hardwick from AgResearch/B3 visited the Hokitika property on Thursday 12 January to assess crop damage and the efficacy of control. We are very grateful to the grower and local rep for the swift reporting which raised this important alert.
All maize growers, in the North and South Islands should be inspecting crops regularly. Control is easier and more effective if damage is identified at the early stages, before the fall armyworm larvae move into the plant whorl.
The photo above show visible damage in the plant whorl and an accumulation of frass (caterpillar faeces).
The maize plants are at the 8-10 leaf stage and the larvae present were large (instars 4-5), suggesting that some had already dropped to begin pupation. Well over 25% of plants were affected at the whorl stage, so the decision to spray was the correct one, based on the threshold guide from international data.
Corn earworm (Helicoverpa armigera) was also present in the in the crop. The pests can look similar, so if you have any doubts, photograph different specimens and send multiple pictures in to MPI.
Over 200 FAW traps deployed by the response group continue to be assessed throughout New Zealand.
National fall armyworm data: as at Friday 13 January, MPI had received 117 enquiries since 1 September 2022. The total number of confirmed positives is now at 56, up 11 from last week. Three of these finds were on the West Coast of the South Island.
The insecticide Sparta (spinetoram 120g/L) is now on label for use on Fall Armyworm in maize and sweetcorn crops for ground applications.
Withholding periods
Maize:
Meat: DO NOT cut for feed, or graze animals intended for slaughter within 28 days after application.
Milk: DO NOT cut for feed, or graze lactating dairy animals producing milk for human consumption within 28 days after application.
Sweet corn:
Sweet corn stover can be grazed post-harvest.
Please contact your local advisor for details on the safe use of this insecticide.
Monitoring and field observations:
- The models indicate that we can expect detections of moths during this week and the next – please continue to check traps and report online.
- Growers and reps should be actively scouting for caterpillars on the crop, do not rely only on the moth catches from traps. As this is still an unwanted organism all findings must be reported to MPI: https://report.mpi.govt.nz/pest or using the app https://www.fi ndapest.nz/ , by email to FAW@mpi.govt.nz or by freephone 0800 80 99 66.
- There are no negative consequences to growers for reporting, as this pest will not be controlled by removing crops.
Thresholds of economic damage
Plant Health Australia provides useful guidance for this:
For useful tools and guides on detection and identification consult FAR website for the latest identification guides https://assets.far.org.nz/blog/files/8a209e4b-4ca8-5338-af06-f3b80bab18e2.pdf and MPI Website www.mpi.govt.nz/dmsdocument/50839-Fall-armyworm-fact-sheet or contact Ivan Lawrie ivan.lawrie@far.org.nz