Pest & disease Factsheet - Whiteflies on ornamentals crops

Whiteflies are sap-sucking insects that can be found in high numbers on protected crops such as tomatoes, cucumbers, peppers, chrysanthemum, fuchsia, abutilon and gerbera. They can also attack outdoor crops including brassicas.

Image: Dove Associates
Image: Dove Associates

They are in the same order and division as aphids and scale insects. Similarly, whiteflies also produce honeydew that can encourage sooty moulds. The adults and larva, or "crawler" stage, feed on plant sap. Some, such as the notifiable tobacco whitefly, are vectors of a wide number of viruses. Some species are showing resistance to some of the key control insecticides, making biological controls even more important.

How to recognise them

There are at least four genera found more often on glasshouse crops:

- Glasshouse whitefly (Trialeurodes vaporariorum), present in the UK since the 1970s, firstly on tomato and cucumber crops then spreading onto a wider selection of plants. Wings tend to lay flat on the body. Eggs are lighter and adults larger than Bemesia tabaci. Secrete larger amounts of wax, making the adults look whiter. More triangular in shape.

- Tobacco whitefly (Bemesia tabaci) is notifiable and has been found throughout Europe since 1986. Wings tend to be held above the body. Eggs are light yellow-brown. Secrete less wax, making the adults look more yellow. More elongated in shape.

- Cabbage whitefly (Aleyrodes proletella), mostly found on outdoor crops but has been found on protected gerbera and cucumbers. Four green/grey patches on wings.

- Strawberry whitefly (Aleyrodes lonicerae) has been found on strawberry, blackberry, raspberries, currants and honeysuckle. Two green-grey patches on wings.

Biology

Multiple generations can be produced on protected crops. Egg, larva and adult stages all live on the underside of leaves and feed on sap, producing honeydew, ultimately weakening crops. There are six development stages, three of which are larval. Eggs are elliptical and deposited in circles. Initial signs of pest presence can be small white powdery deposits on the underside of foliage. Whiteflies can survive year-round under glasshouse conditions.

Symptoms

Sooty mould growth may be the first sign of whitefly activity. Adults are easily disturbed if foliage is moved and will fly up from the plant.

Treatment: biological control

- Encarsia formosa - injects up to 100 eggs into the larval stages. Prefers glasshouse whitefly but will also parasitise tobacco, cabbage and strawberry whiteflies. Infected larvae turn black. Encarsia have black heads and thorax with an orange abdomen. Will host-feed. Prefers lower temperatures and is sensitive to certain pesticides.

- Eretmocerus eremicus - orange in colour. Lays eggs near to larvae that hatch, feed on and develop inside leftover larval "skins". Will attack glasshouse and tobacco whiteflies. Work in higher temperatures up to 30-40 degsC. Not as sensitive to certain pesticides.

- Macrolophus calignosus - predatory bug that feeds on a range of insects with a strong preference for whitefly. Best used early season and prefers plants in Solonaceae family, but it is recommended not to use them on cherry tomatoes. Piercing mouthparts used in conjunction with good vision and searching behaviour.

- Mycotal (Verticillium lecanii) - a biopesticide that works effectively in situations of high humidity by penetrating the insect epidermis.

- Naturalis L* (Beauveria bassiana ATCC 74040) - a biopesticide that can control whitefly along with other pests. Requires 60 per cent humidity and temperature range of 20-30 degsC. Compatible with biological controls.

- Amblyseius swirskii - predatory mite that feeds on a range of pests, pollen and fungal growth. Will feed on glasshouse and tobacco whitefly eggs and larvae at the early stages of infestation. Requires temperatures above 18 degsC to work effectively.

Treatment: cultural control

- Monitor for first signs of pest or damage using yellow sticky traps.

- Label and date them for accurate counts.

- Control weed hosts including common chickweed and sow thistles.

- Good hygiene in between crops, particularly removing leaf debris.

Treatment: chemical control

Active ingredient Acetamiprid

IRAC code 4A

Formulation Gazelle SG (Certis)

Action(s) Insecticide with contact, systemic and translaminar activity. Incompatible with biological controls.

Active ingredient Cypermethrin

IRAC code 3

Formulation Toppel 100* (United Phosphorus)

Action(s) Contact-acting synthetic pyrethroid. Incompatible with biological controls.

Active ingredient Deltamethrin

IRAC code 3

Formulation Various including Decis* (Bayer)

Action(s) Contact pyrethroid insecticide with residual activity. Incompatible with biological controls.

Active ingredient Fatty acids

Formulation Savona (Koppert)

Action(s) Contact-acting insecticide. Compatible with some biological controls.

Active ingredient Flonicamid

IRAC code 9C

Formulation Mainman* (Belchim)

Action(s) Systemic and translaminar activity. Compatible with biological controls.

Active ingredient Imidacloprid

IRAC code 4A

Formulations Couraze (Solufeeds), Imidasect 5GR (Fargro)

Action(s) Systemic insecticide with translaminar, contact and stomach action. Subject to specific use restrictions. Compatible with some biological controls.

Active ingredient Lambda-cyhalothrin

Formulation Hallmark with Zeon Technology* (Syngenta) and others

IRAC code 3

Action(s) Persistent, contact and residual insecticide. Incompatible with biological controls.

Active ingredient Maltodextrin

Formulation Eradicoat, Majestik (Certis)

Action(s) Contact-acting with little residual effect. Compatible with some biological controls.

Active ingredient Nutrient-based plus additional natural products

Formulation SB Plant Invigorator (Fargro)

Action(s) Contact insecticide with physical action. Compatible with some biological controls.

Active ingredient Pymetrozine

IRAC code 9B

Formulation Chess WG* (Syngenta)

Action(s) Insecticide that moves systemically in the plant. Compatible with biological controls.

Active ingredient Pyrethrins

IRAC code 3

Formulations Pyrethrum 5EC (Agropharm), Spruzit (Certis)

Action(s) Short-term knock-down product. Reintroduce predators after seven days.

Active ingredient Spiromesifen

IRAC code 23

Formulation Oberon* (Certis)

Action(s) Contact-acting insecticide for protected crops. Not on Cordyline. Compatible with some biological controls.

Active ingredient Spirotetramat

IRAC code 23

Formulation Movento* (Bayer)

Action(s) Contact and ingested insecticide. Control of adults and larvae can take three-to-seven days. Compatible with some biological controls.

Active ingredient Thiacloprid

IRAC code 4A

Formulations Agrovista Reggae* (Agrovista); Biscaya*, Calypso* (Bayer); Exemptor (Everris)

Action(s) Exemptor can be incorporated into the compost.

Foliar applications incompatible with biological controls.

Fully updated by Dove Associates

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

* Extension of Authorisation 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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