Gout fly management in spring cereals

With stem-boring gout fly highly active in cereals this year, Ellie Dearlove looks at the pest’s life cycle and explains why spring cereals require the closest monitoring right now.

What should you look for?

Gout fly can attack wheat, barley, rye and some grasses.  

There have been reports of serious damage in some winter cereal crops due to the larvae associated with the autumn generation of flies (which are most active in August and September).

We have also seen gout flies at many Recommended Lists (RL) trial sites this year (wheat and barley), whereas we would usually only see them at one or two sites.

This early pressure has boosted the spring generation of adults, with the relatively warm weather encouraging adults to emerge and lay eggs a little earlier than usual.

The spring generation of adults is often most active in May and June.

Despite being small (up to one mm long), it is usually easy to see their eggs with the naked eye.

Look out for white, oval-shaped eggs that have been laid one at a time on the upper side of leaves (often close to central shoots).

It takes about eight to ten days for the eggs to hatch, with the maggots tunnelling into the crop’s main stems and tillers.

Affected tillers may fail to produce ears. Some tillers may also die, with whole plants killed, when infestation is severe.

Once shielded in the plant, pesticides will not be effective.

Unlike wheat bulb fly larvae, where a single larva often attacks multiple shoots, gout fly larvae tend to limit their damage to the original single shoot attacked, which makes well-tillered crops more resilient.

Right now, it is earlier-sown spring crops that are most vulnerable.

For example, gout fly eggs have been spotted recently in spring wheat crops across southern and eastern England.

If maggots attack during tillering, you may notice stunted and swollen stems (which is why it is named ‘gout’ fly).

You may also see yellowing of the affected tillers and leaves with ragged or torn tips.

The most serious damage tends to happen between stem extension and flag leaf emergence (GS32 to 37), so keep a close eye on crops at this stage.

Tips for managing the risk

Act now

• Keep a close eye on late-sown winter wheat and winter barley, and spring wheat and spring barley
• There is no spray threshold for gout fly in spring cereals
• Although there are no approved insecticides for gout fly control in spring cereals, a pyrethroid applied against cereal aphids at the label rate might give some control before larvae move inside the crop
• Leave headlands unsprayed to protect beneficial insects, where possible

Act later

• In higher-risk situations:
• Sow spring crops as early as possible
• For winter wheat and winter barley in sheltered spots (such as fields near woodland), delay sowing until after late September
• Establish crops with higher plant populations, as these can often afford to lose more main shoots to gout fly before yield is impacted
• Encourage natural enemies, as there are several parasitoid species that attack gout fly

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