What you are describing is tank mixing which is not very much encouraged. For the pesticides it leads to cross- resistance in most cases. For biocontrol agents, even if they are all fungi, most market products like Bt. and Beauveria  may have other carrier materials that are not compatible with the other fungi. Unless you have done preliminary work to establish their ability to be used in tank mixing set up. Secondly, you always need a valued reason for tank mixing two fungi, like Beauveria and metarhizium, why would you mix them?..they almost work on the similar pests and it may also not be economical to do this.

Dear Geoffrey,

Trichoderma is a fungal hyperparasite which I would suspect could inhibit your other fungi as biocontrol agents.

If you do a dual culture test you can observe which of these paired are most antagonistic to each other. Ideally some may live and let live and others might be mutually supported. Try the dual culture and let us know.

Thanks for the comprehensive answers Jacinter and paul.....what bacteria with a fungi mixture will it hinder growth of the other.

You should examine their antagonistic effect to each others in vitro, on media such as PDA before attempting to use this mixture in the field. If they do not antagonize each others in vitro, probably they may synergize each others and give high effective biocontrol capabilities against the pathogen. All this will be much clearer after doing the in vitro dual culture technique.

Dear Dr. Geoffrey,

You have to do a dual culture test first. Because there is the possibility of one organism inhibits the growth of other organisms. If both can grow well, then you have to test the effectiveness of the mixture of both. This is important, because not all combination of organisms will provide a better antagonist.

This is what a research mean! Do the treatment combinations as you described and you will see the result and tell us what it is about!!!

I strongly support the observation of Jacinter Atieno Otieno. You should also note that behaviour of organisms may vary when in a rich medium as compared to a spray tank. It is better to apply the two agents separately. Best wishes 

Most has been said already - you will need to test whether they inhibit each other in vitro which is quite likely if one is an antagonistic bacterium and the other compenent is a fungus. Many antifungal substances produced by bacteria are not very specific, and inhibit a broad range of fungi. If it is a combination of fungi you may want to test whether they overgrow and parasitize each other (Trichoderma, Pythium oligandrum) Even if you find negative interactions however, you may give it a try - only a fraction of strains that show in vitro effects exhibit these also in planta, as everyone who works on the development of biocontrol agents painfully knows.

Another question is formulation additives. Additives that are beneficial for one strain may be detrimental to the other as I experienced in my work with antagonists of Eutypa lata that can be downloaded here.

In any case, you need to include also the single strains (preparations) and compare them to the mix (Control, Strain 1, Strain 2, Mix of strain 1 and strain 2)

Dual culture test is a pre-requisite. Mixing strains of different strength of  same species may result in suppressive effect or low effect if one strain is in attenuated form. However, virulent strains of the same species might give a very high effect when mixed together.

I would echo what others suggested, running a dual in vitro test before combining. In addition, if the product is readily available on the market, you may want to read the label carefully and follow the directions. 

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You can test in greenhouse, but you must know, Trichoderma able to mycparasitism other fungi, may be affect on Metarhizium 

It would depend upon the type of the two biological control agents you are using. They may be antagonistic to each other or they may be synergistic. What are the two biological control agents you are using ?

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I think Beauveria do not have any antogonistic against other fungi, but Bacillus or may be some species have antagonistic against fungi

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Hello thanks for the great contributions...Adil Hussain consider the following

metarhizium/beauveria

bacillus subtilis/ metarzium

beauveria / bacillus

trichoderma/bacillus

trichoderma/metarhizium

Check first that neither of the components in the mix are antagonists on the other and rest should be OK.

Yes, a pretest, such as in a laboratory or greenhouse, of possible negative effects and interactions between the two agents as well as results of effectiveness against target pests,  is necessary to evaluate efficacy prior to application. However, the practice is theoretically feasible but not necessarily economically or logistically feasible over long term due to potential unknown negative effects especially for an integrated pest management (IPM) strategy involving alternation of biocontrol-treatments.

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The bacteria  like bacillus have antagonstic against Fungi, but you can try in vitro 

Why don't you try them seperately, the you can try to find the cumulative effect of the ones which show positive effect

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Yes, you can used separately then used toghether

Yes,first find out in laboratory by dual culture. In combination of the insect pathogenic fungi with Trichoderma more caution. Because Trichoderma is an antagonist of the fungi. I attacehd some papers that may help you.

The first step to detect in laboratory is dual culture technique

In my case I had mostly additive effect of interaction of biocontrol agents. (Sometimes synergism or even antagonism) Here is an article:  https://www.researchgate.net/publication/265968557_Single_and_combined_colonization_of_Sclerotinia_sclerotiorum_sclerotia_by_the_fungal_mycoparasites_Coniothyrium_minitans_and_Microsphaeropsis_ochracea

Article Single and combined colonization of Sclerotinia sclerotiorum...

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Can mix together but need to test

If they have  similar niche they can compete. Try to test them first in laboratory for antagonism in vitro and then inoculate on plant you are going to spray and look on disease symptoms severities at mixed and single cultures application and in control without spray.

  for mixing  two  microbes  /formulations of microbes    in vitro studies are to be carried out to determine whether they can co- exist   w/o suppressing other . if they can may be, we can mix both  that could give added effects .  

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you must test a one antagonistic to pathogen then other  antagonistic 

Hello Dear

This idea depend on compatablity of entomopathogen with other bio or chemical substrate. It has to examining before application. Good luck.

When looking at potential for compatibility of biocontrol agents bacteria and fungi often inhibit each other. On the other hand if you use BT endotoxin without any live bacteria it might be very compatible for tank mixture with Beauvaria bassiana. As Laith Al Ani offers up you need to test them out to see their reactions. I use diatomaceous earth with BT and the wounding from diatomaceous earth enhanced the efficacy of the live BT. It is helpful to learn as much as you can about the mode of actions and then test them out. 

Yes, you can mix. But, you need to do an in vitro (dual culture) tests  to see their reactions in the laboratory and do an extended experiment in vivo at various treatment combinations in the greenhouse to establish facts about their compatibility and synergism to know their mode of actions. If you are also using the live cells or enzymes, it also maters. There could be toxicity and  antibiosis reactions that may antagonize each other. Rigorous assessment is required.

Have you tried the combination in the lab?? It doesn't always work. Why did you choose this combnation?/ Did it show good results for each seperately?

It is good idea, however, first look, if  these biological control agents are not antagonising each other.

Good idea!

However, you should look, if these biocontrol agents are not antagonising each other in vitro and into field.

Nowadays consortia of bioagents formulations with synergistic effects on suppression of the target pests are gaining importance. However as said by many workers, lot of preliminary work on the compatibility between the bio-agents, additives used in formulations etc are to be studied.

This is the first pre requisite for consortia formulations.