Grass Grub and Porina. James Buckley Nufarm NZ

Transcription

1 Grass Grub and Porina James Buckley Nufarm NZ

2 Introduction Grass grub and Porina What they look like Biology and life cycle Damage Some of the factors regulating populations Control

3 Grass Grub

4 Adults Roundish, heavy body Light golden brown, 10 mm long Live for 2-4 weeks, feed on leaves Mate on emergence Eggs laid close to point of emergence Generally infestations localised Female can fly to new sites after laying most of her eggs

5 Eggs White, oval ~2mm long x 1mm wide Laid cm deep in the soil Swell by absorbing moisture a few days after laying

6 Larvae C- shaped when relaxed Light tan head with prominent jaws, cream-white body, 6 legs 3 instars Newly hatched 5 mm long Fully grown mm long Soil in gut is visible through skin, white substance is fat. Move up towards surface as they develop 3 rd instars usually less than 50mm deep

7 Pupae Soft bodied Initially creamy white Turn brown as adult develops mm long Found cm deep in soil

8 Typical grass grub life cycle Main period of abundance for each life stage Adults Eggs Larvae Pupae Pasture damage J F M A M J J A S O N D

9 2 year life cycle Main period of abundance for each life stage Adults Eggs Larvae Pasture damage Pupae J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D

10 Grass grub damage Grubs feed on roots in soil High populations will totally destroy plant roots Dead patches, peel back turf Damage typically visible - March onwards 2 nd and 3 rd instars cause most damage

11 Effects of climate High soil moisture in late winter/early spring can cause marked declines in GG populations Severe early summer droughts high mortalities of eggs + young larvae Autumn droughts usually higher larval survival diseases less effect Diseases generally have most impact in late summer/autumn Require temperature (15-20 o C+) and moisture/humidity Diseases generally confined to the root zone in the soil Late summer/autumn is when GG larvae are feeding in this zone

12 Effects of cultivation Cultivation can be used to reduce grass grub numbers Deep ploughing in spring kills delicate pupae Autumn cultivation kills larvae, need repeated surface workings BUT - Cultivation disrupts diseases and greatly reduces predators Natural diseases and predators usually keep grass grub numbers below economic damage thresholds in established pasture Cultivate typically a spike in GG 2-4 years after new pasture sown Avoid cultivating if possible - no-tillage to establish crops/new pasture

13 Assessing populations Need to assess numbers before damage becomes visible to allow timely control and minimise losses Established pasture - in Mid/late February take spade squares (15-20 cm deep) over paddock hand sort 5-7 grubs/spade square ( /m 2 ) ~ threshold level Pasture or cereal establishment - assess numbers before planting 2-3 grubs/spade square (50-75/m 2 ) can cause economic seedling losses especially if established via no-tillage

14 Grass grub control Endophytes Current endophytes available in grasses appear to have little impact on grass grub larvae Little movement of alkaloids down into plant roots Future endophytes????

15 Grass grub control Cultural practices Cultivation can be effective but you may be worse off in the longer term Heavy rolling when grubs up near soil surface can be effective Soil compaction issues??? Stock treading in late autumn/winter Soil pugging and reduced pasture productivity Sow tolerant/resistant species - Lotus, phalaris, tall fescue, cocksfoot

16 Insecticidal control Established pasture Diazinon 20G 11 kg/ha broadcast Short well grazed pasture Grubs close to soil surface within 25mm Moist soil at application and at least 13 mm rain within 7 days for best results

17 Insecticidal control Established pasture DEW L/ha (diazinon) Short well grazed pasture Grubs close to soil surface within 25mm Spray must not dry on foliage apply in rain or irrigation

18 Insecticidal control Pasture or cereal establishment Seed treatments Gaucho, Nuprid, Poncho, UltraStrike, etc Antifeedants, protect establishing seedlings Struggle with high grass grub populations Granular insecticides Counter, Diazinon, Phorate (Thimet) 2-3 months control suscon Green slow release up to 3 years control

19 Granular insecticides Counter at 3-4kg/ha, Phorate at 5kg/ha drilled in furrow with seed Level of control often poor, highly toxic devastating on earthworms Diazinon 20G better control than Counter, Phorate much less toxic 11kg/ha broadcast then incorporated no deeper than 5 cm Drill 5.5 kg/ha into furrow with seed (15cm rows) suscon Green slow release granule, up to 3 yrs control Drill 15 kg/ha in furrow with seed (15cm rows)

20 Insecticide WHP Stock withholding periods Counter, Phorate 6 weeks Diazinon 20G nil suscon Green - 6 weeks Seed treatments 6 weeks DEW nil

21 Porina

22 Porina Wiseanea sp. : Lepidoptera (moth) NZ native - number of species or sub species exist Slightly different lifecycles Found in mixed populations Found throughout NZ Pest - Wairarapa, Canterbury, Otago/Southland, West Coast SI and occasionally in other areas Larvae causes severe plant damage

23 Adult Light brown with distinctive complex whitish markings on wings About 2.5 cm long Short lived females several days, males 4-10 days

24 Eggs 1 mm diameter White when laid Turn black within a day

25 Larvae (caterpillars) 2-3mm long at hatch Limp, flabby Greyish green back, yellowish belly Up to 70 mm long when full grown

26 Pupae Dark reddish brown Cylindrical, blunt ended mm long Found in tunnels prior to emergence

27 Life cycle - adults Adults emerge and fly - spring, early summer or late summer Time depends on species present (several species/subspecies) May change from season to season May be more than one period of adult emergence and flight Fly at dusk & night -strongly attracted to lights Females flutter over pasture dropping about eggs 50-70% eggs laid usually close to point of emergence

28 Life cycle - larvae Larvae hatch 3-5 weeks after eggs layed Live in surface litter for about 6 weeks very prone to dessication When 10-18mm long begin to tunnel in soil Remain in this for rest of larval and pupal stages Tunnel can be 25-30cm deep x 7-8mm wide Emerge from tunnels at night to feed Feed irregularly don t feed when it is frosty Larvae pupate from late spring onwards

29 Porina life cycle Eggs Larvae Pupae Adult Coloured bars indicate periods of peak activity of each of the life cycle stages

30 Factors driving populations Populations mainly driven by survival of eggs and young larvae These are very prone to dessication For high survival of eggs and young larvae need humid environment at base of pasture when they are present Rank pastures with frequent rainfall = ideal conditions Climate has a major impact

31 Damage Larvae chew foliage off at ground level and take it down into burrow Dead plant material - roots left intact Bare areas around burrow Severe feeding pressure Plants die Open patches in sward Bare paddocks

32 Damage Damage Autumn to early Spring - often it will not be visible until pasture growth slows in the winter Damage can occur in pastures free from porina the previous season Level of damage depends on population, pasture type and growing conditions Hay/silage paddocks particularly susceptible

33 Damage thresholds Threshold population size will depend on pasture condition Larvae Number 20/m 2 40/m 2 Pasture less than 4yrs old and open more than 4 yrs old and dense Sward density low adequate Fertility low good Soil Type light heavy Autumn dry wet Previous grazing excessive light

34 Assessing numbers Assess larval numbers in soil spade squares/paddock at least 30 cm deep (burrows can be this deep) Start about 6-12 weeks after adult flights Or early Feb onwards if don t know when flights were Then at about 3 weekly intervals

35 Porina control Dimilin 2L - apply at 50ml/ha Contains diflubenzuron - insect growth regulator stops larvae moulting from one instar to next Continue to feed until they moult Must be eaten (no contact or soil activity) Apply to fresh, short (3-4cm), dry pasture - Dimilin must dry on foliage Target larvae mm long - interval between moults short No larger than about 25mm

36 Porina control Dimilin will kill larger larvae But as moulting interval can be long (1-2 months), pasture damage will continue to occur For larger larvae ( mm long) Use Caterkil 1000 at ml/ha Apply to fresh, short (3-4cm), dry pasture Needs to dry on foliage (very little soil activity)

37 Thank You