Spraying winter wheat after sugar beet for wheat blub fly© Tim Scrivener

Wheat bulb fly egg hatch has kicked off in East Anglia and growers are urged to treat high-risk crops with an insecticide as soon as possible.

The pest is typically a problem in the eastern counties of England, but can also cause issues further north where egg hatch is due to begin imminently.

Adults lay eggs on bare soil in the autumn, which lay dormant until January to March when they hatch and larvae invade cereal crops including wheat, barley and rye.

Plant tillers are attacked at the base of the stem, causing the classic “deadheart” symptoms as the tiller dies and can cause significant yield losses where left unchecked.

See also: Securing the future of a key wheat insecticide

Advisory body Adas monitor egg numbers in soil at 30 sites across the east and north of England and just one was above the 250 eggs/sq m treatment threshold for early- to mid-autumn drilled crops in autumn 2014 – the equal lowest since monitoring began in 1983.

However, Adas entomologist Steve Ellis says the pest is still a threat to crops sown from November onwards – typically those after root crops such as potatoes and sugar beet.

Other high-risk factors include late-drilled crops not treated with an insecticide seed treatment or crops drilled adjacent to fields that sustained attack last season.

“Late drilled crops usually have just one or two tillers at the time of egg hatch, so they are less able to tolerate any losses from larvae attack,” he says.

As a result, crops sown from November onwards or struggling early-sown crops have a lower treatment threshold of 100 eggs/sq m.

Despite the overall low egg counts this autumn, northern monitoring sites in Yorkshire had 53% above the lower threshold and eastern sites only 13%.

“It is usually the other way around, so northern growers with the more damage susceptible late crops should be aware of the increased risk,” says Dr Ellis.

Insecticide treatment

Control of wheat bulb fly is limited to just one active ingredient after the loss of the insecticide dimethoate, which gave growers the chance to kill larvae after they had invaded plants.

Chlorpyrifos, contained in products such as Dursban and Equity, is now the only option and controls larvae at egg hatch ahead of them getting into plants, so timing of the product is critical.

“If the weather is right and you can get on the field, growers should aim to treat in high-risk situations now.” Jim Butchart, Dow AgroSciences

Dow AgroSciences produces its Pestwatch report on its website and gives growers advice on when and how to apply the product.

Dow’s technical specialist Jim Butchart says that growers should assess their risk and where crops meet the correct criteria, aim to treat as soon as possible, where conditions allow.

“If the weather is right and you can get on the field, growers should aim to treat in high-risk situations now.

“It is OK to spray on a frost, but you must be aware of run-off and avoid any situations where there could be a risk of the product getting into water,” says Mr Butchart.

Growers are also advised to use Lerap three-star rated low drift nozzles and adopt a 20m no spray buffer around watercourses or 1m around dry water bodies.

Wheat bulb fly risk factors and control strategy

Risk category

Sowing date




Low (<100eggs/sq m)

No treatment

No treatment

Seed treatment

Moderate (100-249eggs/sq m)

No treatment

Seed treatment

Seed treatment

High (250-500eggs/sq m)

Optional egg hatch spray

Seed treatment and optional egg hatch

Seed treatment and egg hatch spray

Very High (>500eggs/sq m)

Egg hatch spray

Seed treatment and egg hatch spray

Seed treatment and egg hatch spray

Source: HGCA