July/August 2009 – Whitefly Clouds – Is there a solution?

Posted On 04 Aug 2009
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The resistance problem could be compounded if excessive spray programmes and zero whitefly levels are demanded by plant health authorities if plant exports are restricted due to whitefly infestations. Only the tobacco whitefly (Bemisia tabaci) is a Notifiable Pest, whereas glasshouse whitefly (Trialeuroides vaporariorum) is not a quarantine pest. They are easily distinguished by the pupae: glasshouse whitefly pupae are white and have a raised straight edge wall with a circle of waxy filaments on the edge, whereas tobacco whitefly pupae are flatter and are a yellowish colour with less waxy filaments. An intensive IPM programme which includes natural enemies will be just as effective as an intensive pesticide programme and will not leave a residue of pesticide resistant whitefly.

Most of the mature whitefly scales will be on the lower side of the canopy of the plant, so effective under-leaf cover with pesticides is important. Take advice from spray technology experts on whether improvements could be made in spray cover by changing nozzles, pressure and droplet size. More water volume does not always mean better spray cover.

A single female whitefly lays from 100 to 600 eggs depending on the suitability of the host plant. These will hatch and develop into mobile ‘crawlers’ which eventually settle to insert a feeding tube into the leaf. It completes its lifecycle in this final position, by drawing the sugary sap out of the plant. Much of this sap floods out of the ‘other end’ and drips onto the leaf surface below. This sugary solution is an ideal food source for sooty moulds which blacken the surface of the leaf below – reducing yield and quality of flowers. Sooty mould can be washed off with insecticidal soap sprays.

Whitefly adults prefer certain plants such as mint, aubergine, Calendula and tobacco, to many other flower crops. This preference can be used to draw whitefly away from the flower crop, or slow down their movement within or between crops. If biological control agents such as Encarsia formosa are introduced to these trap-crops, then the levels of whitefly parasitoids can build up on the farm. Trap crops must be regularly checked and whitefly found there should be treated with pesticides, bio-pesticides or natural enemies, to prevent these areas becoming infection hotspots for the crops nearby. Calendula is a useful trap for whitefly eggs, as the adults lay many eggs on this plant but few develop into scales – it acts like a whitefly egg sink.

Whiteflies are cold-blooded and need to accumulate a lot of heat from the sun before they are able to fly. By removing old infested crops during the early evening or early morning, when air temperatures are still low, migration from old crops can be almost completely stopped because they are unable to fly at low temperatures. Contact insecticides applied at these times may also be more effective if the adult whitefly do not fly away.

Physical controls such as insecticidal soaps (Savona) can be sprayed under-leaf to destroy the cuticle of the scale and kill the pest by dehydration. Take care to test for phyto-toxicity and avoid spraying in the heat of the day to prevent scorch. Potato starch dextrin (Majistick) has also been used to kill whitefly scales by osmosis, drawing out water from the body of the whitefly to dilute the more concentrated starch solution. Majistick can be integrated with the use of Encarsia because parasitised pupae are not affected.
Entomopathogenic fungi such as Lecanicillium lecanii, Paecilomyces fumosoroseus and Beauveria bassiana are biopesticides for whitefly. Fungal spores land on the whitefly and are able to germinate, penetrating the whitefly and growing in its body fluids. These fungi generally need a relative humidity of 75% for at least 10 hours after application in order to germinate. Careful timing of the fungicide programme in relation to the biopesticide applications needs to be taken care of because these are themselves fungi and could be killed by some fungicides.
The predatory mite Amblyseius swirskii is a new biocontrol for whitefly control, but according to Wageningen University researchers, it should be used in conjunction with Encarsia because A. swiskii prefers to prey on the whitefly eggs and crawlers. Encarsia is still needed at six Encarsia per meter square per week, to combat the second, third and forth whitefly larvae stages. Encarsia is more susceptible to insecticides and fungicides – so a well designed spray programme for other pests is essential. Wageningen recommend that if swirskii is used in roses, that the slow release bags are more effective than the loose swirskii products because it is more difficult for swirskii to build up in the crop (if there are only low whitefly populations) if the loose product is used. The bags are more expensive and at least 4,000 slow release bags are needed per hectare, replaced every 6 weeks to provide effective control. The best reproduction of swirskii occurs if both thrips and whitely are present at the same time. It will not control high infestations of whitefly. There is minimal survival of swirskii and no population growth at temperatures below 15 deg C and minimal growth at 18 deg C. Other predators such as Macrolophus, will eat all stages of whitefly but they belong to the capsid family and care needs to be taken if capsid cause damage in the crop.

If the parasitic wasps, such as Encarsia formosa and Eretmocerus are being used, more care needs to be used in the deployment of yellow sticky traps, as they are also attracted to yellow sticky traps. Most bio-control companies offer these parasitoids and their websites can be referred to for detailed programmes. (www.syngenta-bioline.co.uk and www.biobest.be). High introduction rates of Encarsia adults at an introduction ratio of 1 adult Encarsia to 20 whitefly scales on the crop, will force the Encarsia to ‘sting out’ the scales, making them drop completely off the crop. This might be a preferred way of using this parasitoid, if the customer does not want to see black scales on the leaf. Since Encarsia is one of the cheapest bio-control agents for whitefly, this may still be the most economic way of controlling whitefly.




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IPM input

type

Information on IPM of WHITEFLY

Encarsia    formosa

parasitic wasp

Whitefly should only be a hotspot problem in greenhouse crops.  If it has spread throughout the greenhouse – this is probably because hot spots have not been treated quickly with biological control.  Encarsia can treat both Bemisia whitefly and Trialeuroides whitefly, if used prophylacticaly at high rates – to optimize the ‘stinging-out’ action of the parasitoid.  Seek advice from Real IPM on introduction strategy.  The objective is to have clean leaves – with few black, parasitised scales.  Introduce at one Encarsia ADULT (not black scales) to 20 whitefly scales found on leaves from scouting data – apply same rate weekly until all whitefly scales have been killed (and drop off  leaf). Most whitefly in rose crops, tend to be on the lower canopy – where conditions are good for Encarsia.  Encarsia is best used for hotspot treatments rather than total crop treatments. Encarsia very sensitive to fungicides and insecticides.  Seek advice.

Beauveria   bassiana

fungus            which kills insects

Use Beauveria as a targeted spray at the lower canopy only – as it is not compatible with Phytoseiulus and other bio-controls – so don’t spray entire canopy unless absolutely necessary.  It is NOT persistent in the canopy and is killed by UV light.     Beauveria is more appropriate for control in greenhouses where the whitefly has got ‘out of control’ and is widespread rather than in hotspots (where Encarsia is used).    Do not try to mix Beauveria and Encarsia in the same place.  No recorded resistance of whitefly to Beauveria.  Application rates 1 kg per ha per week, as advised.  Do not tank mix with other pesticides and do not use an adjuvant with Beauveria – take care to integrate with fungicides carefully – seek advice from Real IPM.

Cultural

traps

Trap crops (mint and Calendula) grown 10 meters away from the outside of the greenhouse and sprayed every late afternoon (between 4 to 6 pm) will lure and kill whitefly.  If sprayed with Beauveria, the whitefly may even carry the Beauveria with them if they move into the crop – and infect other whitefly inside.   Use yellow sticky traps in a horizontal position above the crop (not vertical – as this could PULL whitefly INTO the greenhouse – if seen from outside).   Do not remove whitefly infested crops during warm weather, as clouds of adult whitefly will move off it onto other crops.  Whitefly cannot fly in the cold – remove crops in early hours of morning or evening (with lights).

Compatible pesticides

Whitefly is very prone to resistance.  Rotate IRAC groups carefully.  Do not spray the same pesticide more than once in a row.  Careful scouting and prompt action is necessary.  Starch or detergent sprays can help kill whitefly – seek advice from Real IPM on strategy.   IPM programmes are essential for control of whitefly.

       

 

 

 

Whitefly (page 1)

IRAC

 

WHO class

Phytoseiulus persimilis

Amblyseius   cucumeris

Orius

EPNs

Encarsia

Aphidius

Cryptolaemus

Trade name

active ingredient

%

death

persist

(wks)

%

death

persist

(wks)

%

death

persist

(wks)

%

death

persist

(wks)

%

death

persist

(wks)

%

death

persist

(wks)

%

death

persist

(wks)

Methomex

Lannate,

methomyl

1A

IB

>75%

4 wks

>75%

6-8 wks

>75%

8-12 wks

>75%

?

>75%

6-10 wks

>75%

8-12 wks

?

?

Nogos

dichlorvos

(fog)

1B

IB

>75%

zero

>75%

zero

?

?

<25%

zero

>75%

1 wk

>75%

?

?

?

Confidor

imidacloprid

(drip line ONLY)

4A

II

25-50 %

2 wks

<25%

zero

>75%

4-6 wks

<25%

zero

>75%

2 wks

<25%

zero

<25%

zero

Confidor

 

imidacloprid  (spray harmful)

4A

II

>75%

2 wks

>75%

zero

>75%

?

<25%

zero

>75%

2 wks

>75%

zero

>75%

>4 wks

Calypso

thiacloprid       (drip line ONLY)

4A

II

25-50 %

?

<25%

?

25-50 %

?

?

?

25-50 %

?

25-50 %

?

?

?

Calypso

thiacloprid       (spray harmful)

4A

II

50-75%

2 wks

?

?

>75%

2 wks

?

?

50-75%

?

50-75%

?

>75%

?

Actara,

thiamethoxam (spray harmful)

4A

?

50 – 75%

>2 wks

?

?

?

?

?

?

?

?

25-50%

?

?

?

Actara

thiamethoxam  (even drench harmful)

4A

?

50–75%

>2 wks

?

?

>75%

>2 wks

?

?

50-75%

?

25-50%

?

?

?

Golan,      Mospilan

acetamiprid     (drip line ONLY)

4A

? II

<25%

zero

<25%

zero

25-50%

1 wk

?

?

25-50%

?

<25%

?

?

?

Golan,       Mospilan

acetamiprid   (spray harmful)

4A

?II

50 – 75%

1 wk

50 – 75%

1 wk

>75%

2-8 wks

?

?

>75%

>2 wks

50–75%

>2 wks

50 – 75%

>2 wks

Enstar II

kinoprene

7A

O

25-50%

?

<25%

?

50-75%

?

 

 

25 – 50%

0.5 wk

?

?

<25%

?

Admiral

Juvinal

pyriproxyfen

7C

U

<25 %

zero

<25 %

zero

<25 %

zero

?

?

<25%

?

<25%

zero

25-50%

?

 

 

 

 


Whitefly (page 2)

IRAC

 

WHO class

Phytoseiulus persimilis

Amblyseius cucumeris

Orius s

EPNs

Encarsia

Aphidius

Cryptolaemus

Trade name

active ingredient

%

death

persist

(wks)

%

death

persist

(wks)

%

death

persist

(wks)

%

death

persist

(wks)

%

death

persist

(wks)

%

death

persist

(wks)

%

death

persist

(wks)

                                   







Chess

pymetrozine

9B

?

25-50%

zero

<25%

zero

<25%

zero

<25%

zero

25 – 50%

zero

50-75%

?

?

?

Pegasus

diafenthiuron

12A

U

>75%

1 wk

50->75%

?

25-50%

3 wks

<25%

zero

>75%

?

>75%

1 wk

<25%

zero

Nomolt

teflubenzuron

15

U

<25 %

zero

<25 %

zero

>75%

4 wks

<25 %

zero

<25 %

zero

<25%

zero

?

?

Applaud

buprofezin

16

U

<25 %

zero

<25 %

zero

<25 %

zero

<25 %

zero

25-50%

4 days

<25%

zero

25-50%

?

Cyroguard

cyromazine

17

U

<25 %

zero

<25 %

zero

<25 %

zero

<25 %

zero

<25%

zero

<25%

zero

?

?

Nexter

Sanmite

pyridaben

21A

III

50-75%

?

>75%

?

?

?

?

?

>75%

2 wks

?

?

?

?

Oberon

spiromesifen

23

?

50-75%

4-12 wks

?

?

<25%

zero

?

?

<25%

?

<25%

?

?

?

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