Green beans 2
Chewing pests

John D. Duff, Department of Primary Industries and Fisheries, Queensland.

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Introduction

Green beans are grown all year in Queensland, on the Granite Belt during summer; Lockyer Valley and surrounding regions during spring, summer and autumn; Gympie and Bundaberg during autumn, winter and spring; and the Bowen and Burdekin districts during autumn, winter and early spring. Bean production in southern parts of Australia is restricted to the warmer months of late spring, summer and early autumn.

Apart from being sensitive to cold, thus restricting where beans can be grown, they are also sensitive to attack from a wide range of insect pests, from the moment the seed germinates (root aphid), to when they are harvested as pods (heliothis and bean pod borer). Where beans are grown can also dictate the types of insect pests and the degree of infestation expected.

To minimise the impact of insect pests on plant growth and yield some management options must be used. Using only pesticide sprays regardless of the pest level is neither efficient nor desirable. Unsuitable pesticides may create insect pest problems by killing beneficial insects such as parasitoids and predators. A list of potential beneficial insects can be found in the DPI&F Note Green beans 4: Beneficial insects in an IPM system. 

Integrated pest management (IPM) is the preferred approach for crop protection. IPM uses preventative measures and cultural and biological control options in conjunction with appropriate use of pesticides. Detailed information on IPM in green beans and how best to apply it to your situation can be found in the DPI&F Notes links, under Further reading below.

There are two groups of insect pests of green beans. Those described in this DPI&F Note that chew parts of the plant and include caterpillars, beetles and a fly grub, and sucking insects that suck sap from the plant and include whitefly, various bugs, aphids and mites.

Chewing insect pests

There are a number of chewing pests that attack green beans, Table 1 lists them and the part of the plant they attack. The major chewing insect pests are bolded, the other pests occur only sporadically or cause minor damage.

Beetles

Only three types of beetles were consistently found feeding on green beans, and only on the leaves. They were Apion species, a small round black beetle, 2 to 3 mm long with a narrow snout which it uses to penetrate the outer layer of leaf tissue, it eats close to the leaf surface causing a small crater in the leaf. Chaetocnema species, a flea beetle and Phyllotreta undulata the striped flea beetle are both characterised by their large hind legs, similar to a flea, which they use to propel themselves off the leaf surface when disturbed. Flea beetles are 1 to 2 mm long and can make small holes in the leaves.

The red-shouldered leaf beetle Monolepta australis (Figure 1) can occasionally be found in the crop but damage is generally minimal. When they occur in swarms damage can be significant, but is generally over a limited area and time period. This beetle is about 7 mm long and yellow brown with a red spot on each wing cover and a red strip across the base of the wing or shoulder region as the name suggests.

Figure 1. Red shouldered leaf beetle

Flies

A large number of flies can be found in green bean crops. However bean fly (Ophiomyia phaseoli) is the only fly that is known to cause significant damage to the bean plants, particularly at the seedling stage. Bean fly can be found during most of the growing season but is generally a more significant pest towards late summer and into autumn. Depending on the region, bean fly can still be a pest during winter.

The adults, Figure 2, are small, about 2.5 mm long and shiny black, they lay their eggs into the upper surface of the leaf near the petiole and stem. The larvae or maggots tunnel into the stem (Figure 3), causing the young plants to collapse. Older plants can also succumb to this pest, damage is generally seen as cracking along the stems and leaf axils, making them prone to breaking under windy conditions. The dark brown 2.5 mm long pupae can sometimes be seen in the cracked stems.

Figure 2. Bean fly adult on a bean leaf

Figure 3. Bean fly larvae in bean stem

Moths and butterflies

There are five pests from this group known to attack green bean crops. The grass blue butterfly Zizina labradus damages new growth by chewing holes in the leaves. It can also cause small holes on the developing pods but the larvae do not enter the pods as heliothis and bean pod borer do. The adult is a relatively small blue grey butterfly and can be seen flying around legume weeds and lucerne. The bluish eggs are heavily dimpled and flat. The grubs appear slug like and slow moving. They are relatively small, up to 10 mm long, and green with two pale green strips along their back, they are covered in dense short hairs.

Vegetable looper, Chrysodeixis argentifera and another looper Mocis alterna also attack the leaves of green beans. Vegetable looper grubs (Figure 4), have a green body, the older grubs have paler lines running along the length of their body. The Mocis looper is more slender, the whole body and head is striped pale green and khaki, however there are variations to the colour of this looper. As the name describes they arch or loop their bodies when they move bringing their rear end forward before moving the front of their bodies forward. These caterpillars can grow up to 35 mm long before they pupate.

The most serious pests of green beans are heliothis, both Helicoverpa armigera and H. punctigera, and bean pod borer Maruca vitrata. These pests attack both the flowers and developing pods, or burrow into the pods to feed on the developing seeds. Once in the pod control is impossible with conventional insecticides, and damaged pods are rejected by the pickers or sorters.

H. armigera is resistant to a wide range of commonly used insecticides, making it an even more difficult pest to manage. Heliothis is a problem during most of the growing season in the Lockyer Valley region, but is only an issue for growers in the northern growing region during autumn and towards the end of the growing season. Heliothis caterpillars (Figure 5), can grow to more than 30 mm long in a variety of colours, but are predominantly green to brown with distinct stripes running along the length of the body.

Bean pod borer is generally only a problem in late summer and autumn. It does identical damage to heliothis so can easily be confused with heliothis damage if you are not familiar with it. The caterpillars (Figure 6) grow up to 18 mm long, are a cream colour with rows of dark brown spots along the body and have a dark brown head capsule. The moth has a slender pale brown body and rests with its wings out stretched Figure 7.

Figure 4. Vegetable looper larva

Figure 5. Heliothis larva on a bean

Figure 6. Bean pod borer larva

Figure 7. Bean pod borer moth

Further information

DPI&F Notes

Other DPI&F Notes in this 'Green beans' series include:

• Green beans 1: An integrated approach to pest management
  
  

• Green beans 3: Sucking pests          
  
  
• Green beans 4: Beneficial insects in an IPM system
  
  
• Green beans 5: Crop monitoring
  
  
• Green beans 6: Cultural practices in an IPM system
  
  
• Green beans 7: Biological management options in an IPM system
  
  
• Green beans 8: Chemical management options in an IPM system
  
  
• Green beans 9: Pesticide application

Other publications

• Cantrell, B.K., Donaldson, J.F., Galloway, I.D., Grimshaw, J.F. and Houston, K.J. (1983). Survey of beneficial arthropods in potato crops in south-east Queensland. Queensland Journal of Agricultural and Animal Sciences. 40(2):109-119.
  
  
• Llewellyn, R. 2000. Sweet Corn Insect Pests and their Natural Enemies, an IPM Field Guide.
  
  
• McDougall, S., Napier, T., Valenzisi, J., Watson, A., Duff, J., Geitz, G. and Franklin, T. 2002. Integrated Pest Management in Lettuce: Information Guide. (NSW Agriculture, Orange, NSW).
  
  
• Mound, L.A. and Gillespie, P. 1997. Identification Guide to Thrips Associated with Crops in Australia. (NSW Agriculture, Orange, NSW).
  
  
• Pyke, B.A. and Brown, E.H. 1996. The Cotton Pest and Beneficial Guide. (GOPRINT, Woolloongabba).
  
  
• QDPI. 1996. Managing Insects and Mites in Horticultural Crops. (Department of Primary Industries, Brisbane).
  
  
• Scholz, B. (1998). Integrating natural enemies into heliothis management. In: Insect Pest Management in Sweet Corn, Workshop No. 1, 19-20 May 1998 at the Gatton Research Station, Queensland.
  
  
• Swaine, G., Ironside, D.A. and Corcoran, R.J. 1991. Insect Pests of Fruit and Vegetables, 2^nd edition. (Queensland Department of Primary Industries, Brisbane).
  
  
• Wood, P.; Ferguson, J.; Brown, E.; Cahill, M.; English, M.; Brennan, L. and Elder R. 2000. Crop Insects: The Ute Guide Northern Grain Belt Edition. (Department of Primary Industries, Queensland).

DPI&F information and services

• To access DPI&F's information and services, Queensland residents can contact the DPI&F Business Information Centre on 13 25 23 for the cost of a local call, from 8 am to 6 pm Monday to Friday (excluding public holidays). E-mail callweb@dpi.qld.gov.au. Non-Queensland residents phone (07) 3404 6999.

• Current national information on agricultural chemicals registered for use on all crops is available on the Infopest CD-ROM. Write to DPI&F, GPO Box 46, Brisbane, Qld 4001, E-mail infopest@dpi.qld.gov.au, visit the Infopest web page, or phone (07) 3239 3967 for further information.

Industry links

• Industry links is a page of links to various sites of interest to horticultural growers.

Acknowledgements

Much of the information included in this document has been developed through projects  facilitated by HAL in partnership with AUSVEG and DPI&F and funded by the vegetable levy. The Australian Government provides matched funding for all HAL's R&D activities.

Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.

Last reviewed 05 November 2007