Helicoverpa can attack soybeans at any stage from seedling to pod ripening but are most likely to attack flowering/podding/podfill stages.
|Insects and damage
- Vegetative soybeans are more attractive to helicoverpa than the vegetative stages of other summer pulses
- Helicoverpa populations (>6/m2) can inflict serious damage in vegetative crops as they target the plant’s axilliary buds which are the precursors to the floral buds.
- Helicoverpa also attack soybean flowers and pods. However soybean pods are less succulent as those of other summer legumes, and young larvae feed initially on leaves before attacking pods.
- Do not confuse with loopers (loopers have 2-3 pairs of ventral prolegs; helicoverpa have 4 pairs)
- Don’t confuse with cluster caterpillar (both have 4 pairs of ventral prolegs, but cluster caterpillars are fatter and smoother with 4 rows of distinctive black spots).
- Learn to differentiate between H. armigera and H. punctigera. H. armigera is the dominant species in the northern region (Dubbo north) while H. punctigera predominates in the south. However significant numbers of H. armigera can infest late summer soybean crops in the south (south of Dubbo). Correct identification is important for management planning, as the species have different levels of resistance.
|Monitor and record
||Monitor crops at least weekly during the vegetative stage and twice weekly from flowering onwards.
- Monitor vegetative crops more frequently in hot weather
- Monitor with a beat sheet. Sweep nets are not practical in soybeans because of the crop’s dense canopy.
- In crops with narrow row spacings (50 cm), consider using a light-weight beat tray.
- The sampling unit is one metre of row. Helicoverpa (and other pests) are dislodged from plants with a 1-metre long beat stick.
- Sample 5-6 widely separated sites across each crop, and take 4-5 random one-metre samples within a 20 m-radius at each site
- Look for helicoverpa eggs and for damage, including leaf chewing, terminal damage and damage to pods, and any natural enemies of Helicoverpa.
- Open vegetative terminals to check for small larvae feeding inside.
- Beat sheet sampling may detect only 50-70% of small larvae but sampling inefficiency is likely to be cancelled out by high mortality rates of young larvae.
Record the number and size (e.g. small, medium, large)
- Record the stage of crop development (to estimate time to harvest).
- Convert helicoverpa counts per metre to helicoverpa per square metre by dividing pest numbers by the row spacing in metres.
- Record beneficial insects
- Consider presenting recording data in a visual form (graphs) to track pest and beneficial populations over time
||Be aware of the many beneficials attacking helicoverpa:
- Trichogamma wasps parasitize Helicoverpa eggs
- Microplitis, Heteropelma, Netelia sp. and other wasps parasitize helicoverpa larvae.
- Predatory bugs such as big-eyed bug and damsel bug prey on eggs and small larvae
- Glossy shield bug and spined predatory shield bug attack larger larvae.
- Ants and spiders will also attack helicoverpa larvae.
- To conserve beneficials, adopt the “Go Soft Early” IPM strategy of only using biopesticides against caterpillars in vegetative crops.
- A number of natural occurring fungal and viral diseases in the soil can infect larvae.
- Adopt good agronomic practice as more vigorous crops are better able to compensate for helicoverpa damage.
- Helicoverpa punctigera is a migratory species which proliferates on native plants in central Australia therefore control of local hosts have no impact on this species.
- Set harvester up to screen out damaged seeds
- Cultivation of paddocks following harvest will help control helicoverpa pupae
||Helicoverpa thresholds in soybeans are based on potential yield loss
- Yield loss is due to damage to the plant’s axilliary buds which are the precursors to the floral buds
- In vegetative crops, soybeans can tolerate up to 7 larvae/m2 with no yield loss. Above this, yield penalties are severe, hence thresholds are set at 6 larvae per square metre. Reduce this threshold in seedling crops.
- Thresholds in flowering/podding soybeans are based on a yield loss of 40 kg/ha per larvae/m2
- Threshold tables developed for helicoverpa in soybeans allow for variations in crop value and cost of control. Values typically range from 1-2 larvae/m2
See also the Economic threshold ready reckoner for helicoverpa in soybean
||Vegetative crops, pre-flowering.
- Unless populations are very high (≥12/m2) in vegetative crops, use NPV-based biopesticides.
- Ensure good coverage and target larvae <12 mm long, ideally <7 mm.
- Add an Aminofeed or equivalent feeding stimulant adjuvant to maximise efficacy.
- Vegetative thresholds show that 100% helicoverpa control is not required to protect soybean yield in vegetative crops.
- Selective insecticides are the preferred options to preserve beneficials
- Ensure good spray coverage for ingestion active insecticides
Where both H. armigera and H. punctigera occur in soybeans (mostly from Dubbo south) be aware that insecticide resistance in H. armigera can affect the efficacy of SPs and OPs in mixed helicoverpa populations.
- Control of H. punctigera with synthetic pyrethroids (SPs) and organo phosphates (OPs) can flare mites and aphids as these formulations kill natural enemies of these pests
- Control of H. armigera with carbamates can flare silverleaf whitefly, mites and aphids
- To avoid flaring whitefly, mites and aphids, as well as helicoverpa, adopt the ‘Go Soft Early’ IPM strategy of using biopesticides against caterpillars in vegetative crops, and the more-selective insecticides in flowering/podding crops.
- Delay spraying of podsucking bugs until podfill, as no soft options are available for these pests
||An Area Wide Management approach to monitor the arrival H. punctigera (e.g. pheromone trapping) and management of insecticide resistance (H. armigera)
A national network of pheromone traps for adult Helicoverpa is maintained during migration periods, and results are reported in PestFacts, PestFax and the Beatsheet.
Industry publications provide up to date regional information about pest activity in crops.
Insect pest management in soybeans (DAF Qld)