SCEPTREplus: Legumes

Controlling Bean Seed Fly in legumes

• Crop: Vegetable crops including legumes
• Target: Bean Seed Fly
• Period: May 2018

Take home messages

• Growers should ensure that weed or cover crop growth has died back before cultivation and seedbed preperation, and that there is little to no green organic material in soils
• A period of 2 to 3 weeks in advance of planting is sufficient to allow decomposition of residues
• When preparing soil for planting beans, some advisors recommend leaving about an inch of dry, well cultivated soil on the surface as it may be unattractive to the egg-laying flies
• Sowing seeds into warm, dry soils promotes rapid emergence and shortens the time that seeds are exposed to attack by bean seed fly
• The use of reduced cultivations and stale seedbeds may aid management of bean seed fly. However, there is also a suggestion from colleagues in other parts of northern Europe that increasing problems with bean seed fly might be related to use of non-inversion and minimal tillage approaches, which is in contract to some of the studies identified in the review
• Bean seed fly is more of a problem when susceptible crops are planted in succession and it is therefore advisable not to plant sucessive susceptibe crop species 

Trial summary

Bean seed fly can be a pest of a wide range of crops, but is particularly damaging currently to legumes and alliums. Management of bean seed fly has always been challenging. In recent years the most effective insecticide treatments have been seed treatments. These have relied on a limited number of active ingrediments and generally one active ingredient has been available for each crop. If thes treatments are lost for whatever reason, it leaves growers in a very vulnerable position. This has occured recently in terms of the chlorpyrifos seed treatment on Phaseolus beans and thiamethoxam seed treatment on pea; for both crops treated seed was imported to the UK. This work reviews studies on insectiidal control and also considers other potential management/control techniques for bean seed fly to identify further options that might be investigated within the SCEPTREplus project or in other ways.

Conculsions

• Bean seed fly is a problem on a range of crops in various parts of the world
• Cultural control methods have been evaluated on a number of crops and this is certainly an approach worth exploring in more detail for specific UK crops as part of an integrated control strategy 
• Information on the timing of peak periods of fly activity may also be useful to growers 
• Of approaches to control bean seed fly with insecticides, seed treatments are undoubtedly the most effective way of reducing bean seed fly damage (depending on the active ingrediment) However, several studies suggest that in-furrow treatments of appropriate insecticides may provide a useful level of control 
• Much of the research on insecticides has used active ingredients that would not be approved for this use in the UK. Two insecticdes that are approved on oter crops in the UK (chlorantraniliprole and cyantraniliprole) have shown potential, but their use for bean seed fly control would depend on a new method of application (either as an in-furrow treatment or a seed treatment) It is also possible that other insecticides, not tested previously against bean seed fly, may be identified for inclusion in SCEPTREplus trials 
• Control with garlic formulations and nematodes has been investigated. The garlic formuations proved ineffective. It may be worth investigating the application of entomopathogenic nematode products available in the UK.

• Crop: Vining peas and green beans
• Target: Broad-leaved weeds
• Period: Mar-Sept 2019

Due to the loss of important active ingredients to control broad leaved weeds in vining peas and dwarf green beans it has become imperative that effective alternative materials are identified that may be suitable for future EAMU or full approvals in the future. 

Conclusions

The low weed numbers and/or species that emerged in both pieces of work limit the conclusions that can be drawn.

All treatments appeared to be crop safe in both pea and green bean trials, but nothing of statistical significance can be drawn from the pea work regarding weed control due to low levels of weeds.

The uneven emergence may have masked some treatment effects as past PGRO work has identified aclonifen as a material that can significantly affect emergence. Where significant control of weeds was seen in the green bean work pre-emergence AHDB9917, pre and early post emergence sprays of AHDB9898 and applications of AHDB9987were the most promising and worthy of further investigation.