Tropical Grass Webworm monitoring
Latest results
29 April 2008
Monitoring was completed today with pheromone traps being collected and temperature data logger info downloaded onto the computer. However feeding damage continues north of Waipapakauri with large numbers of moths seen at night (2 moths also seen on the window at Cable Bay on 27 April). Damage is occurring at sites where it has not been seen since 1999. Most of the damage occurring south of Pukenui. There are large numbers of moths in rank kikuyu grass and in kikuyu grazed pasture.
Moths caught in pheromone traps 18 – 29 April
Motutangi:
- Harrington East – 9 moths
- Harrington West – 26 moths
- Blucher – 9 moths
- Bilott – away on holiday
Ngataki - 11- 18 April:
- Corner trap – 6 moths
- Macrocarpa trap – 37 moths
Ngataki - 18 – 29 April:
- Corner trap – 11 moths
- Macrocarpa trap – 3 moths
Rainfall - 18 – 29 April: Blucher – 11 ml
Number of immature TGW per square metre at Blucher site – 44 larvae, 19 pupae.
Minimum temperatures in kikuyu thatch went below the threshold of development (11 C) from 18-25 April but have risen again (14.2-17.4 C) in the last 4 nights (26-29 April). Today it is hot, sunny and humid again with the bad weather now to the south.
If these warm night temperatures continue then TGW, which is active at night, will continue to cause damage. However we are close to May and temperatures should drop soon.
Previous results
18 April 2008:
It has continued to be humid and warm on the Aupouri Peninsula – 170ml of rain was collected in the rain gauge at Motutangi from 4-18 April.
There is still damaged kikuyu pasture in the Waiharara, Motutangi and Pukenui areas. Usually in warm sheltered areas if kikuyu is short and is coming away again in the favourable growing conditions.
Moths caught in pheromone traps in the two weeks from 4-18 April
- Harrington East – 34 moths
- Harrington west – 34 moths
- Blucher – 28 moths
- Bilott – 40 moths
There are large numbers of moths about in rank pasture and also in short grazed pasture. Number of immature TGW recorded per square metre kikuyu pasture at Motutangi – 34 larvae and 7 pupae.
Damaged patches of kikuyu in Turk Valley Rd are now being grazed by horses and there is kikuyu regrowth opposite the Bilott property east of SH1F.
Whether there will be an increase in damaged areas will depend on weather in the next week or two. If warm conditions continue then TGW will continue to breed and feed but there may be some colder weather coming up from the south which will curb the growth of TGW populations
As at 4 April 2008
Trap catches at Ngataki (21 – 28 March 2008):
- Corner trap – 24 moths
- Macrocarpa trap – 22 moths
- Ngataki 28 March – 4 April
- Corner trap – 8 moths
- Macrocarpa trap – 23 moths
Trap catches at Motutangi (26 March – 4 April):
- Harrington East – 7 moths
- Harrington west – 1 moth
- Blucher – 14 moths
- Bilott – 10 moths
Rainfall Blucher 26 ml
Number of immature TGW per square metre kikuyu pasture on 4 April at Bluchers - 29 larvae and 6 pupae.
At 50 immature TGW per square metre TGW damage becomes obvious and pasture appears as if has been treated by herbicide.
There are numerous areas of TGW damaged pasture including;
- Turk Valley Rd
- Harrington East and west of SH1F
- Pasture east of SHiF opposite Norm Bryan and Bilott property
- Bilott property
- Houhora heads
- Hukatere Rd
- Kuhtz property – Ngataki
Temperatures will start to cool and it is hoped that this will slow TGW development and feeding activity especially at night.