Pest & disease management - Aphids on protected crops

Rapid maturation and feeding damage on ornamental plants contribute to aphids' importance as pests.

With their pear-shaped bodies, long antennae and a pair of rear-end siphunculi (also described as "exhaust pipes"), aphids are one of the most easily recognised and common glasshouse pests. All aphid species are sap-sucking. Some have a wide host range while others are restricted to specific plants or plant types.

In most species, females can produce live young without mating, as well as lay fertilised eggs. Live young can mature to adults in as little as one week. The variety of ways that aphids can wreak plant damage — distorting and reducing growth, transmitting viruses and producing sticky honeydew — also contribute to their economic importance as pests.

Aphids feed by probing plant cells with their filamentous mouthparts, sucking up sugar-rich sap from phloem tissue. Because they have to ingest large amounts of sap to obtain enough nitrogen, the excess sugar is excreted as honeydew, providing the ideal environment for sooty moulds.

Biology

Most species have two types of plant host — one on which they overwinter in some form, such as eggs, and the second to which adults fly in spring and on which much of the feeding damage is done.

New generations of winged aphids migrate between seasonal host plants or fly to find fresh feeding grounds when colonies become overcrowded. Temperature plays an important role in determining the speed with which aphids complete life cycles and the build-up of populations.

Treatment: biological control

- Peach-potato and melon-cotton aphids (round-bodied aphids) — Aphidius colemani or A. matricariae parasitic wasps Best used as a preventive treatment, introduced early in the season.
- Glasshouse-potato and potato aphids (elliptical-shaped aphids) — Aphidius ervi or Aphelinus abdominalis parasitic wasps Introduce at first sign of aphids. Aphelinus is slower-acting than Aphidius ervi.
- Aphidoletes aphidimyza predatory midge larvae Adults need dark periods for mating, whereas the larvae need 15 hours of daylight to avoid triggering diapause, the mechanism by which pupae overwinter.
- Chrysoperla carnea, a native lacewing Introduced as larvae that are avid predators of aphids. Best used against established populations in hotspots and as complementary control to Aphidius and Aphidoletes.
- Adalia bipunctata The ladybird.

Treatment: cultural control

- Monitor for first signs of pest or damage especially on newly emerging foliage.
- Use yellow sticky traps to monitor the adult flying stages.
- Spectral filter polythene claddings are available that may modify aphid feeding behaviour.

Treatment: chemical control

Some commercial neonicotinoids are restricted in their use on crops considered attractive to bees including ornamentals "flowering in the year of treatment". Exceptions include commercial products in glasshouses and as foliar treatments after flowering.

Ornamental crops that have some crossover include almond, apple, apricot, peach, nectarine, pear, plum, quince, sloe, blackberry, blueberry, gooseberry, raspberry, cherry, Castanea sp., currants, grapes, hazelnut, Actinidia, citrus, olives and some outdoor herbs. Other products available include:

- Gazelle SG and others (acetamiprid) Insecticide with contact, systemic and translaminar activity. Not included in neonicotinoid restrictions. Compatible with most biological controls.
- Naturalis-L (Beauveria bassiana) Primarily for whitefly and thrips control with limited effect on aphids. Compatible with biological controls.
- Toppel 100* and others (cypermethrin) Contact- and stomach-acting pyrethroid insecticide. Incompatible with biological controls.
- Decis* and others (deltamethrin) Contact pyrethroid insecticide with residual activity. Not compatible with biological controls.
- Danadim Progress (dimethoate) Contact and systemic organophosphorus insecticide. Incompatible with biological controls.
- Sumi-Alpha and others (esfenvalerate) Contact pyrethroid insecticide with residual activity. Incompatible with biological controls.
- Savona (fatty acids) Contact-acting insecticide. Compatible with most biological controls.
- Imidasect 5GR, Couraze (imidacloprid) Compatible with most biological controls. Included in neonicotinoid restrictions.
- Hallmark WZT* and others (lambda-cyhalothrin) Fast-acting, persistent, contact and residual insecticide. Incompatible with biological controls.
- Eradicoat or Majestik (maltodextrin) Contact insecticide with physical action. Use as an overall spray 24 hours before introducing biological control agents.
- SB Plant Invigorator Contact insecticide with physical action. Compatible with most biological controls.
- Aphox and others (pirimicarb) Contact and translaminar activity. Compatible with most biological controls.
- Chess WG* (pymetrozine) Prevents aphids feeding, killing them in one-to-four days. Compatible with most biological controls.
- Pyrethrum 5EC and others (pyrethrins) Short-term, contact insecticide extracted from natural pyrethrins. Compatible with most biological controls.
- Calypso*, Biscaya*, Exemptor (thiacloprid) Not included in neonicotinoid restrictions. Compatible with some biological controls.
- Actara* (thiamethoxam) Contact and systemic properties. Not compatible with biological controls. Included in neonicotinoid restrictions.

Fully updated by Dove Associates

Use plant protection products safely. Always read the label and product information before use.

* EAMU required for use in ornamental plant production outdoors and/or under protection.
Dove Associates shall in no event be liable for the loss or damage to any crops or biological control agents caused by the use of products mentioned.


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