Insecticides - Best Practice to Minimise the Environmental Impact in Arable Crops

Crop and Pest Control Strategies

Reproduced by courtesy of the HGCA from its publication Arable cropping and the environment a guide, 2002

Crop & Pest

Threshold

Treatment Strategy

Cereals

Autumn aphids
  • High risk of aphids and BYDV forecast.
  • Aphids in crop late Oct/early Nov.
  • Delay drilling until mid-Oct.
  • Destroy previous crop residues to remove 'green bridge'.
  • Apply spray treatment 5-6 weeks aftercrop emerges.
  • If mean daily temperature <3C and remains low, sprays may not be needed.
Summer aphids
  • >50% stems infested and increasing at stem extension to flag leaf emergence.
  • 66% of ears/stems infested and increasing at flowering to watery ripe.
  • Use half-rate insecticide if threshold is exceeded, parasitoid activity is low and <2% aphids are mummified.
  • Do not treat if >5% are mummified.
Wheat bulb fly

Millions of eggs/ha.

  • <1 no action.
  • 12.5 damage possible on late-sown crops.
  • 2.55 economic damage very likely.
  • >5 damage inevitable.
  • Do not cultivate fields due for wheat from late July to end of wheat harvest.
  • Increase seed-rate and choose variety more suited to high-risk situations. Use seed treatment or egg-hatch spray if necessary.
  • Consolidate soils after earlier cultivation to avoid rough tilth.
Orange wheat blossom midge

Cocoons/kg soil.

  • 1140 moderate risk.
  • >40 high risk.

Midge numbers/ears.

  • 1 midge/3 ears (feed wheat).
  • 1 midge/6 ears (milling or seed wheat).
  • Monitor at ear emergence if risk is high, soil is wet and >13C in May.
  • Consider an insecticide at ear emergence if threshold is exceeded.
Frit fly

>10% of plants attacked at 12 leaf stage (wheat after grass).

  • Destroy grass or grass weed infested stubbles at least 6 weeks before drilling.
  • Only apply insecticide at 12 leaf stage if threshold is exceeded.
Leather jackets

5 leatherjackets/m of row highest risk with spring cereals but only when drilled after ploughed out grass.

  • Monitor susceptible crops sown after grass for first month after crop emergence.

Oilseed rape

Cabbage stem and flea beetle

5 larvae/plant Nov/Dec or 50% petioles scarred.

Damage by adults is most severe on slow-emerging or poorly established crops.

  • Only apply treatment if adult damage is very severe at the cotyledon stage, and/or threshold is exceeded later in autumn.
Pollen beetle

Beetles/plant:

  • 15 at green/yellow bud stage on winter crops.
  • 5 on slow-growing, backward crops.
  • 3 on spring crops.
  • Apply pyrethroid insecticide if threshold is exceeded.
Cabbage seed weevil

Weevils/plant:

  • 2 during flowering on winter crops.
  • 1 in northern England and Scotland.
  • 0.5 in the north if a fungicide required or significant pod midge damage likely.
  • 2 at any time from green bud to late flowering on spring crops.
  • Apply a pyrethroidat the correct timing if threshold is exceeded.

Peas and Beans

Pea and bean weevil

Damage most likely on spring beans, less on winter beans and peas. Slow-emerging crops are particularly susceptible.

  • Only treat with an approved pyrethroid if leaf-notching is severe and growing points are attacked.
Pea aphid 20-30% of shoots infested between first flower and pod-set on 4th truss (combining peas)
  • Apply a single pirimicarb spray if threshold is exceeded.
  • Take numbers of natural enemies into account.
Black bean aphid
  • 5% plants infested on south-west headlands pre-flowering.
  • 2.5% of plants infested across whole field and colonies spreading to pods.
  • Treat spring beans with pirimicarb if above threshold pre-flowering. From flowering onwards, treat only if colonies are so large as to spread down stems and onto pods.
  • Do not treat winter beans.
Pea moth

>10 moths in one of a pair of pheromone traps on two consecutive occasions.

  • Apply approved pyrethroid spray if threshold is exceeded (combining peas for seed or ware for human food).

Potatoes

Potato cyst nematode (PCN)

Eggs/g soil:

  • 110 no treatment.
  • >58 treat intolerant varieties.
  • 1160 treat all varieties.
  • >60 eggs/g treatment essential and significant yield loss is still likely.
  • Ensure crop is well-fertilised and watered to limit damage.
  • Apply full-rate nematicide to crops where threshold is exceeded, even to PCN-resistant varieties.
Aphids
  • Seed crops: zero tolerance.
  • Ware crops: no threshold as crops generally tolerate infestation provided no false top roll occurs.
  • Seed crops: apply routine treatment programme from 80% crop emergence.
  • Ware crops: monitor varieties prone to false roll top and treat with pirimicarb if rapid increase in aphid numbers.
  • Treat other varieties if >30 aphids/leaf.

Sugar beet

Peach potato aphid

Aphids/plant:

  • 0.25 plants with <12 leaves.
  • 1 plants with >12 leaves.
  • Use combination of seed treatment, granular insecticides/nematicides at planting and foliar sprays (usually pirimicarb).
  • Do not treat plants with>14 leaves.
Black bean aphid

>25% of plants infested and colonies increasing.

  • Use combination of seed treatment, granular insecticides/nematicides at planting and foliar sprays (usually pirimicarb).
  • Do not treat plants with>14 leaves.
Free-living nematodes

200 nematodes/litre of soil can be damaging. Mainly a problem on light sandy soils and in a cold, wet spring.

  • Analyse soils for nematodes.
  • Apply nematicide if levels are sufficiently high.

All crops

Slugs
  • Higher risk on heavy soils with surface trash, especially if direct drilling.
  • Thresholds are difficult with slugs. For cereals pre-drilling catches of 4 or more slugs/trap over  3 days indicates a high risk of damage.
  • Use baited traps to monitor slugs.
  • Ensure good drilling conditions. Roll seedbeds.
  • Test bait susceptible potato varieties in wet seasons.
  • Apply molluscicides when slugs are active.

This guide has been produced as part of the Voluntary Initiative by the Crop Protection Association. The Association would like to thank Peter Thompson of Game Conservancy Trust, the British Crop Protection Council and its members for its valuable technical input and the Homegrown Cereals Authority for permission to reproduce the section on Crop and pest control strategies.

Reproduced for ADLib Feb 2004 under Licence.

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