Pest Spray Thresholds

When should cereals be sprayed for Gout Fly?

Spray if more than 50% of plants at GS12 have eggs.

What is the spray threshold for Grain Aphid in cereals before GS61?

Spray if 50% or more of tillers are infested.

What is the spray threshold for Grain Aphid in cereals from GS61 until two weeks before grain fill?

Spray if 66% or more of tillers are infested.

When should an aphicide be applied for BYDV in cereals?

Spray when 170 day‑degrees have accumulated since crop emergence or the last aphicide spray.

What is the Orange Wheat Blossom Midge threshold for milling wheat?

Treat if there is 1 midge per 6 ears.

What is the Orange Wheat Blossom Midge threshold for feed wheat?

Treat if there is 1 midge per 3 ears.

At what wireworm density should cereal seed be treated with Signal 300 ES (cypermethrin)?

When more than 750,000 larvae per hectare are detected.

When should slug pellets be applied in cereals?

Apply pellets if 4 or more slugs are found per refuge trap (contains layers mash).

What is the pollen beetle spray threshold in oilseed rape crops with fewer than 30 plants m²?

Treat when there are 25 beetles per plant.

What is the pollen beetle spray threshold in oilseed rape crops with 30–50 plants m²?

Treat when there are 18 beetles per plant.

What is the pollen beetle spray threshold in oilseed rape crops with 50–70 plants m²?

Treat when there are 11 beetles per plant.

What is the pollen beetle spray threshold in oilseed rape crops with more than 70 plants m²?

Treat when there are 7 beetles per plant.

Why is the threshold for pollen beetle in OSR higher the less plants there are per m²?

A lower crop density results in larger plants with more branches and therefore more pods as each plant has a larger individual area and so can better compensate for pollen beetle damage (tolerate more before there is a meaningful impact on yield).

Why is the threshold for pollen beetle in OSR lower the more plants there are per m²?

A higher crop density results in smaller plants with less branches and therefore less pods as each plant has a smaller individual area and so is less able to compensate for pollen beetle damage (tolerate less before there is a meaningful impact on yield)

When should cabbage seed weevil be sprayed for OSR grown in the north of the UK?

Spray if more than 1 weevil is found per 2 plants.

When should cabbage seed weevil be sprayed for OSR grown in the south of the UK?

Spray if more than 1 weevil is found per plant.

What is the spray threshold for mealy cabbage aphid in winter oilseed rape?

Treat if 13% of plants are infested.

What is the spray threshold for mealy cabbage aphid in spring oilseed rape?

Treat if 4% of plants are infested.

When should pea aphid be sprayed for in combining peas?

Spray if 20% of plants are infested.

When should pea aphid be sprayed for in vining peas?

Spray if 15% of plants are infested.

What is the spray threshold for thrips in peas?

Treat if there are 4 thrips or more per plant and the crop cannot outgrow the damage.

What pea moth trap result triggers detailed monitoring in combining peas?

10 moths caught across both pheromone traps on two consecutive visits.

What daily data must be recorded after the pea moth threshold is reached in combining peas?

The maximum and minimum temperatures for each day.

How is pea moth egg development assessed in combining peas once monitoring starts of max and min daily temperatures?

Use the pheromone‑trap egg development calculator to calculate the daily percentage egg development.

When should the first spray be applied for pea moth control in combining peas?

When cumulative egg development reaches 90%.

When should the second pea moth spray be applied in combining peas?

Two weeks after the first application.

What is the pea moth spray threshold in vining peas?

Apply a single spray at the flat‑pod stage if 1 moth is caught in the traps.

When should silver Y moth be sprayed for in peas?

Treat if 50 or more moths are caught by first pod set.

What is the spray threshold for black bean aphid in beans?

Spray when 5–10% of plants have colonies.

When should the first spray for bruchid beetle be applied in beans?

After two consecutive days with temperatures above 20°C during pod formation.

When should the second bruchid beetle spray be applied in beans?

Seven days after the first application.

What is the spray threshold for slugs in potatoes?

Treat if 1 slug is found per trap (contains layers mash).

What is the spray threshold for peach‑potato aphid in sugar beet up to 12 true-leaves?

1 aphid per 4 plants.

What is the spray threshold for peach‑potato aphid in sugar beet between 12 and 16 true-leaves?

1 aphid per plant.

When should sugar beet be sprayed for beet leaf miner?

When the number of eggs plus larvae per plant exceeds the square of the number of true leaves per plant.

What is the spray threshold for silver Y moth in sugar beet?

Treat if more than 5 caterpillars are found per plant.

What is Hutton criteria for treating late blight in potatoes?

For two consecutive days, the minimum temperature must be at least 10°C, and there must be a minimum of six hours each day with relative humidity at or above 90%.