Clever ResearchGate. I am not sure who is responsible for converting this answer to a question, but thank you, whoever it was! This indeed is the crux of the matter. One important addition to this question is that the whitefly control must be EXTREMELY effective, since whiteflies on cassava in sub-Saharan Africa transmit disease-causing viruses, and these viruses can be extremely damaging. In our particular case, we are also struggling with the issue that the cassava we are producing is for the supply of 'healthy' and certified commercial multiplication and dissemination systems. This means that we have a virtual zero tolerance for virus infection, which in turn means that we need extremely low whitefly populations (less than 1 adult per shoot apex). If anyone has some thoughts on how this might be achieved, it would be great to hear.

Thanks for the response, Carolin. We have one main Encarsia species (E. sophia) here in Tanzania which parasitizes B. tabaci on cassava. The other main one is Eretmocerus mundus. Obviously, as soon as we put any chemicals on the cassava to tackle the whiteflies, this is likely to damage natural control from these parasitoids. The problem with these natural enemies, however, is that they are not able to control wf populations to the level required to stop virus transmission. They account for up to 50% of B. tabaci mortality, but this is still not nearly enough. Partly because of this, we are currently working on introduced Eretmocerus hayati which we hope will greatly strengthen natural control of B. tabaci, based on promising experience obtained elsewhere, notably in Australia. Even that, however, is unlikely to give us enough control to produce seed crops of cassava with very low or zero virus infection levels. This is why we really do have to go a route involving more direct control.

Dear James Legg,

I really understand your situation regarding white fly control...in your case erradication. I strongly believe that counting only with natural methods you will never be able to control B. tabaci population. White flies are a cosmopolite pest with several alternative hosts, fast life cycle, and they are resistant to many different chemical compounds (Insecticides), including secondary plant metabolites.

You did not mention which irrigation method you are using in your experimental area. In particular cases the adoption of sprinkler irrigation can reduce a little bit more the population size but not enough for your case. If you are concerned for instance with the experimental condition, the use of big walk-in cages can help you a lot.

Hope you have success there and good luck!

Hi Dr. Legg,

I recommend that you use entomopathogenic fungi such as Isaria fumosorosea (=Paecilomyces fumosoroseus) biopesticide (PFR 97, Preferal, Prefered) along with the parasitoids. The fungal insecticide has been demonstarted to be benign to beneficials and is compatible as part of an IPM strategy. Do you have access to these products?

Dear James Legg,

I have done some research about biopesticides on two spotted spider mite in greenhouse conditions. But I do not know that can these results be useful for you or not? So, if you want to know about our results I can send some of them to you.

Hi James

we have developed a biocontrol agent against twin spotted red spider mite (usually about 70% elimination of TSSM), and which is extremely effective against whitefly, usually >90% elimination. See the research papers by Gatarahiya et al.

What is special about the product is (a) the strain of Beauveria bassiana: it is best of 650 isolates screened for their activity as an entomopathogen; (b) the formulation. The problem is that conidia of Bb are hydrophobic and therefore do not mix well in water. In fact, they will clump together instead of being dispersed in water. So the product needs to be carefully formulated with a dispersant agent. Its biocontrol activity and level of effectiveness is a function of the quality of spraying, so we would recommend use of a mist blower with a fine droplet size, applied weekly, and with the addition of Breakthru, a silicone wetting agent.

It is registered and commercially available in South Africa and Zambia as Eco-Bb by Plant Health Products (Pty) Ltd (www.plant-health.co.za).

Given your need for complete control, and given that the efficacy of biocontrol agents varies with the environmental conditions, and especially with variable humidity, I would also recommend combining it with imidocloprid drenches, which are effective for several weeks, I believe. And by not spraying it on, the imidocloprid will not affect predatory insects.

The combination of imidocloprid, predatory insects and an effective biocontrol agent should provide extremely good control levels, and will reduce the chances of resistance development.

Mark Laing

Very helpful response Mark. Since we have a base in Zambia, we might just try to purchase some for experimental purposes. Any plans for the producers to apply for a license in other countries, such as Tanzania? The point about imidacloprid application is a good one. We have done this in the past for whitefly control, but have unwisely got into the happen of spraying more recently. East to switch back, and should hopefully have an immediate beneficial effect on predatory mites. T. aripo is well established in Tanzania, but we will certainly need to augment what might already be present in the fields in Tanga region, which are the ones under discussion here. Thanks again for the helpful comments.

Hi James,

yes, PHP is looking for a distributor in Tanzania. When that happens, they will need to secure a registration as per Tanzania's requirements. In the meantime, it is registered in Zambia - - - .

The interesting thing about the neonicotinamides is that they seem to be taken up well as drenches and distributed systemically. I think that if this is the case generally, (am I correct ?).

If it is true, then the suppliers of this class of insecticide could head off the substantial problems that they face with bee deaths globally, by recommending their application by drenching or seed treatment only. This should / would save the predatory insects and bees that are being affected by off-target drift of sprays at present.

That is, unless the neonicotinamides insecticides translocate into pollen and nectar, even if applied by drenching or seed treatment., which would affect bees anyway.

Mark

I had heard about the concerns over neonicotinoids in Europe, in relation to effects on bees. You would think that there must certainly already be research results demonstrating how these chemicals impact bees. Perhaps we therefore need to scan the literature? What would be the procedure for testing Eco-Bb in Tanzania?

Hi Pasco, similar to the question to Mark above, what would be the procedure for accessing PFR97 for tests here in Tanzania. I'm am sure there are no local distributors. It is actually quite common to see Paecilomyces wipeouts of whiteflies on cassava in East Africa, particularly in Uganda where I used to be based, but these would not be viable products as the duration required for applications and the relatively low abundances of whiteflies required for virus transmission would make it uneconomic - bearing in mind also that most cassava production in East Africa is subsistence oriented. Our clean seed fields are an unusual exception in this sense, as we need to ensure that they remain as near as possible free of virus.

Hi James, PreFeRal (=PFR 97 in the States) is available through Biobest in Belgium; also if you can isolate samples of infected/mycosed whiteflies in the field, you can then grow them on agar plates, allow to sporulate, collect and then use in a preliminary test to see if would work for you senario. ICIPE should also have some Isaria fumosorosea and other entomopathogenic isolates. Another alternative may be to use a trap crop sprayed with the fungus to reduce the population from coming in contact with the cassava. Incidently, a recent paper by Lacey et al. showed that when potato psyllids were infected with PFR 97, the transmission of zebra chip bacterial disease was significantly reduced in the field. I have also found that when the Asian citrus psyllid and other pestiferious insects are infected with the fungus, that they stop feeding. I will be glad to send you copies (PDFs) of the articles.

Hi James, I've scanned this thread and it seems there are a number of biological approaches suggested. The only chemical control suggested that I noticed was imidacloprid. However, I think that might not be very helpful for the mite part of the problem. Depending on the dynamics of biocontrol of mites there, imidacloprid and indeed other neonicotonoids might further release mites from natural controls. If you are looking for a single compound to address both Bemisia whiteflies and mites, I can think of only a couple options. Spiromesifen (a lipid biosynthesis inhibitor) is active against whiteflies and spider mites, particularly at the highest dosages. It will not provide direct control of whitefly adults, which may be an issue for a vectored virus situation. But perhaps when used at low whitefly densities, it would provide a level of protection against both pests for you. There is also a mite IGR, etoxazole, which is excellent on spider mites. It does not have major effects on whiteflies, but I suspect at a high enough dose it will provide benefits in whitefly control, too. Either product is likely to be more compatible with any other biological approach you select (fungi, parasitoids, etc.) than imidacloprid or any other neonicotinoid. Hope this helps. --Peter

Hi Peter, That is certainly very helpful information. We are hoping that switching from foliar spraying to soil drenching will help with the Imidacloprid problem of exacerbating the mites, however, the alternatives that you suggest sound like they would be signficantly better. The only issue for us is actually getting hold of products such as these. There is a 99% certainty that these are not available in Tanzania, and importing them prior to their registration in the country might be problematic. Since I have very little experience of working with pesticides, I will need to consult with colleagues here in Tanzania that so, as I am sure that are ways of getting around this, by importing small quantities for evaluation purposes or the like. It would be really helpful if you could indicate where we might be able to buy the two products that you mention, and if you happen to have any info on suggested dosages, that would be helpful too. Thanks again for a very helpful response!

Very simple go for the complete wetting of the plant with a rain gun you may add 0.03% sandovit a spreader for dissolving the web underwhich they shelter & are difficult to control. do it 3x at 3 -5 days interval You will get an excellent control of the tetranychus spidermites.or use an yeast extract Abamectine Vertimec 0.5ml/lt .Iif you have a problem of white fly & mites & would like to release predatory mites in Cassava then go for soil drenching of 2-3 kg/acreThiovit 08 WDG thru drip irrigation as it will reduce the soil EC value and there is a direct correlation of soil EC with the White fly attack and spray a selectice pesticide which will kill both W fly & mites & protect spredatory mite & parasites of w flies Encarsia & Retomocerus) using a Thiourea compound of Syngenta sold as POLO or PEGASUS at 0.5-0.75 gms /lt water.very specific for both mites & white flies.Take care not to allow the eyes geting in this pesticides usinga spect. Further one need to see wheteher there is a registration & label claim of this product by the govt in your country . To some crops Polo/pegasus is phytotoxic please try on a small area 1-2metre see the phytootxicity till a week if there is no phyto then go ahead if it is registered & have a label claim on that specific crop in your sountry.

u can use easy, safe, effective and cheap methods to control mites and white fly

1- azadirachtin (formulated neem) which is specific to control sucking pests and have some side effect on mites with law PHI period.

2- abamectin 1.8% which considered bio-pesticide effective against mites and white fly.

3- using water with liquid potach soap for both pests if the populations were small

Also, u can mix azadirachtin with little amount of abamectin it will be effective

Dear James,

I have encountered a similar problem in North India on cotton with overlapping infestation of the red spider mite (Tetranychus?) along with whiteflies (Bemisia).There is the additional problem of resistance to a range of pesticides including neo nicotinoids. Given your need for eco friendly control, I would not recommend Imidacloprid. Perhaps a better choice would be to control the nymphal stage of Bemisia with Diafenthiuron (Syngenta's Polo). Underleaf coverage and the addition of a silicone surfactant will help improve results.

However, if you want an eco friendly means to suppress both pests in an area where resistance to pesticides is not a problem, I have introduced a botanical based on Karanjin which does the job adequately and also suppresses thrips and sooty mould fungus, a common undesirable side effect of sever infestation by sucking pests.

As far as control of the virus is concerned, I have introduced another product - Helios, which does the job very well. I do not of any pesticide which can control fungi, bacteria and viruses as well as Helios does.

If you like I can send you some samples for trial if you can apy the courier charges. I used to head a leading agro chemical company in India, but for the last 5 years, I have made it my mission to introduce cost competitive eco friendly practices to boost farm gate profitability and production. The areas I am concentrating are pest and disease management though non chemical means as far as possible, reduced use of chemical fertilisers, drought protection of crops and microbial measures to treat solid and liquid effluents.

A couple of years ago, I started work on managing die back of citrus caused by Phytophthora citrii and helped reverse this disease and resurrect orchards that were severely infested.

Kind regards,

Uday Philar

I have developed a package of water jetting in mulberry garden by diverting a portion of irrigation water to control the sucking pests. The system is very Effective, Economic and Eco-friendly. Please refer my article "Comparative efficacy of water jetting and chemical measures against major sucking pests of mulberry and their safety to natural enemies" in Journal of Biopesticides (2011), 4(2):219-230, available online (www.jbiopest.com/users/LW8/efiles/vol_4_2_270C.pdf). Periodical spray of strong jet of water in cassava garden help to keep the population of spider mites as well as whiteflies below economic injury level without application of any insecticides. This approach also washouts the black sooty moulds as well as the dust sediment on the leaves which enhances the photosynthetic activity of the plant and hence the practice

plays additional role in increase of crop yield. The jetted water irrigates the garden simultaneously.

With Regards

N.Sakthivel

Yes, this works where holdings are small. I have used this against other sucking pests like mealy bugs. However, I have found it difficult to implement in the case of larger holdings and in situations where irrigation resources are scanty.

Dear Uday

Water jetting using high volume sprayer is cumbersome because it needs to fetch bulk quantity of water. It is time taking and expensive too and therefore not suitable for larger holdings. But in this system water is diverted from irrigation pipeline by which we will get uninterrupted supply of water as well as sufficient flow quantity to generate adequate water pressure to hit the pest lethally and wash them out from the plants. Hence, the system is user-friendly and highly suitable for large scale application. Many sericulture farmers in Tamil Nadu (India) is practicing water jetting using this method successfully.

With Regards

N.Sakthivel

U can use also the sulfur as dust which effective against mites and repellent to insects and could be considered as fertilizer and make kind of worm to plants

The azaracditina has proven an insect growth regulator that acts as a factor which controls pests antifeedant through starvation and growth arrest. Effectively controls mites, thrips, aphids, whiteflies and leaf miners.