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Aphid feeding damage

Table of registered insecticides

Damage

• Aphid feeding can cause direct damage, in the absence of the plant virus BYDV, by reducing yields by up to 10 per cent and by reducing seed size, leading to a possible downgrading of the grain quality.
• Damaging populations may develop in potentially high-yielding crops (3 t/ha or more) in an average of one out of three years.
• Direct feeding damage occurs when colonies of aphids develop on stems, leaves and heads, from the seedling stage through to head filling.
• The degree of damage depends particularly on the percentage of tillers infested, the number of aphids per tiller and the duration of the infestation.
• There may be no obvious symptoms while aphids are feeding and causing direct damage. Heavily infested plants may turn yellow and may be covered in a sugary honeydew produced by the aphids, and on which black sooty moulds may develop.
• Much larger yield and quality losses can be sustained when crops are also infected with BYDV.

Control

• Parasitic wasps, ladybirds, lacewing and hoverfly larvae can provide useful biological control of aphid feeding damage at lower aphid densities.
• When aphids are in moderate to high densities, these predators and parasites are usually unable to control an increasing population, although given the right conditions certain fungi may kill a large proportion of the population over a short period of time. The use of 'soft' insecticides such as pirimicarb that selectively kill aphids is advocated if damage thresholds are reached.
• For decisions on whether or not to spray insecticides to prevent aphid feeding damage, crops should be checked from late tillering onwards for oat aphids on stems, undersides of leaves and ears and for corn aphids in the furled growing tips. Walk through the crop in a W pattern, noting the numbers of aphids per tiller at every few paces.

Insecticides

• THRESHOLD: Spraying with an approved insecticide is worthwhile if 50 percent of cereal tillers have 15 or more aphids and crops are expected to yield 3 tonnes/ha or more.
• Click here for a table summarising registered insecticides for use in controlling both BYDV spread and aphid feeding damage.
• Crops sprayed before Zadok's growth stage 30 (start of stem elongation) should be checked again 3-4 weeks after spraying as aphids may re-establish and build up again to threshold levels.

Page reviewed: 22 March 2006