Native budworm populations are patchy, regionally speaking

Pheromone trap catches across south-eastern Australia have declined in the last two weeks. Sweep net monitoring of budworm larvae reveal densities ranging from very low to moderately high

Native budworm caterpillar (left) and moth (right) (Source: cesar)

 

Where have they been reported?

In the Victorian Mallee, pheromone trap catches of the native budworm moth (Helicoverpa punctigera) have generally declined over the past two weeks relative to those observed in early-mid September. Trap catches in Victoria’s Wimmera, Northern Country, Central and South West districts, and NSW’s Riverina and Central West Slopes and Plains have also been low, suggesting minimal egg-laying in these areas.

Reports of crop monitoring for native budworm reveal a range of infestation levels of the larval stages. In the Victorian Mallee (Ouyen), many pea crops have budworm larvae at or above threshold and have been sprayed. The larvae ranged in size from 3 to 10 mm and are likely to have arisen from August moth flights. Vetch, with a current value of over $1000/t, is also being sprayed for budworm larvae. Numbers have been low in canola and lupin crops. In the Victorian Wimmera, most pulses have been checked but there are no signs of budworm larvae.

About native budworm

For comprehensive information on native budworm, including their occurrence, lifecycle, behaviour and management strategies, go to Native Budworm within the new PestNote series. 

Forecast modelling and budworm growth rates

Our predictive modelling tool (Darabug) uses average temperatures from a range of meteorological stations from which to generate forecasts of budworm development rates. Based on the dates of the latest peak moth catches (albeit very small catches in many cases), the predicted dates for third instars are as below:

Victoria

Central and South West: 11 November

Wimmera: 30 October

Eastern Mallee: 21 October

Northern Country: 01 November

NSW

Riverina: 23 October

Central West Slopes & Plains: 22 October

Third instar larvae are relatively easily seen in sweep nets (3 to 5 mm long) and relatively easily controlled, particularly with biologically active insecticides. Fifth instar larvae, which is the stage in which most seed damage begins, typically appears about a week later.

In cases where predictions were made from very low catches, predicted egg lay dates are less reliable. This is because these moths may have arrived much earlier, or possibly, emerged locally. The majority of moths caught in pheromone traps are expected to be recent immigrants that will typically mate upon arrival and soon after begin egg lay.

Our Advice

The recent hot conditions will have brought flowering of most crops to an end, and should curtail budworm egg-laying. Nonetheless, monitoring crops should begin from early podding, particularly after the predicted date for third instar larvae.  

Monitor crops regularly using sweep nets; it is important to sample representative parts of the entire paddock prior before making a control decision. Taking multiples of 10 sweeps within at least five locations in a paddock is recommended. Important note: sudden hot days can drive young caterpillars directly into pods.

Economic thresholds for native budworm should be followed. These vary according to crop, control costs and anticipated crop return. Comprehensive and dynamic economic thresholds have been developed for native budworm in pulses/legumes in Western Australia. These should also apply to south-eastern Australia. Table 1 provides an example, assuming cost of control at $10/ha. Control is warranted if the cost of control is less than the value of the yield loss predicted. With the increase in grain prices over the last 12 months, economic thresholds have decreased.

Table 1: Yield loss estimates for five pulses and corresponding economic thresholds (ET) for native budworm

	K – Loss for each larva in 10 sweeps (kg/ha/larva)	P – grain price ($/tonne)	C – cost of control ($/ha)	ET – larvae per 10 sweeps
Field peas	50	400	10	0.5
Lentils	60	680	10	0.3
Faba bean	90	500	10	0.2
Chickpeas - desi	30	600	10	0.6
Canola	6	450	10	4.0
Lupins	7	420	10	4.0

 

Sources of field reports of native budworm

Brad Bennett – Agronomist, AGRIvision Consultants (Victorian Mallee)

Ben Cordes – Agronomist, Tylers Hardware & Rural Supplies (Victorian Wimmera)

Luke Maher – Agronomist, AGRIvision Consultants (Victorian Mallee)

 

Acknowledgements

We thank the following for providing various forms of support to this forecast service:

Institutional Support

• Prof Peter Gregg and Dr Alice del Socorro  – School of Environmental & Rural Science, University of New England, Armidale
• Bill Kimber and Helen DeGraaf – SARDI
• Alex Mills – Adama Australia Pty Ltd

Trap operators/facilitators

• Brad Bennett  – Consultant, AgriVision (Victorian Mallee)
• Jim Cronin – Agronomist, Landmark (NSW Central West Slopes and Plains)
• Allan Edis – Agronomist, Landmark (NSW Riverina)
• Anna Fry - Trainee Agronomist, SHC (Victorian Mallee)
• Bill Gardner  – Agronomist and Grower, (Victorian Wimmera)
• Shayn Healy – Agronomist, Crop Rite Pty Ltd (Victorian Mallee)
• George Hepburn  – Agronomist, Tylers Hardware & Rural Supplies (Victorian Wimmera)
• Neil Hives – IPM consultant central, southern and western Victoria (based in Central Victoria)
• Damian Jones – Irrigated Cropping Council (Victorian Mallee)
• Jake Leith – Tech Services Agronomist, AgriVision (Victorian Wimmera)
• Rob Sonogan  – Consultant, AgriVision (Victorian Mallee)
• Greg Toomey  – Agronomist, Landmark (Victorian Northern Country)
• David & Lachlan Trewick – Growers (Victorian Northern Country)
• David White – Agronomist, Delta Agribusiness (NSW Riverina)