The problem is that there does not exist a single text that addresses all your needs. Some texts deal with only specific plant types (houseplants, vegetables, conifers, etc.) and some texts deal only with diseases OR pests but not necessarily both. And a great many have no illustrations at all but are just factual in nature. And then there is the issue of regionality.......a great many resources are focused on specific areas (in my experience, different regional areas of the US), as diseases and pests tend to have a very regional or locale-specific basis rather than a global one.

There are some decent online sources, but again, I think a great many are focused on a specific part of the world - how relevant they would be for your purposes I couldn't say.

Are there any professional organizations or universities in your area that present or teach these subjects? That may be a way to get some basic knowledge of the issues you are most likely to encounter specific to your location and situation. Or if you focus your search on a specific plant type, you can often find information unique to that plant via an online resource.

Thanks for your input gardengal48. I know about the regional issues, that's why I mentioned where I live. (Un)fortunately where I live is essential in many other aspects, one of them being the total lack of recent and original information on a local level. As far as I know there are no such specific courses and I am not about to spend 5 years on a masters degree in agriculture just to know how to get rid of the fungusamongus without poisoning the plants and myself :)
Another reason I don't want to get my info locally is that I want to be better than the rest, better than those who know only what is written in Bulgarian some 20 years ago, rewritten and remixed or more recently - chopped from here and there and half-translated, scattered across forum posts or posted with the sole purpose of promoting some newer product.
So more ideas are welcome!

The internet has far exceeded the information that my books have to offer. As a professional and as an educator, I have amassed hundreds of excellent books over the years, all of which collect dust on the bookshelves.

Even nursery management and container plant culture information can be found on line.....with up to date best practices.

It's important to understand that discussions about plant diseases must emphasize prevention and culture. So, evaluating the growing conditions, sanitation, planting medium, etc., should come before anything else. It makes no sense to be armed with solutions to plant diseases when you don't know what might be contributing to the occurance.

Anyway, what kinds of plants are you growing?

Actually I never had any devastating disease problems with my plants. Most of the plants I lost (and these were no more than only a few dozens over the past 4 years) during the winter months because I wasn't able to provide adequate conditions - lack of space, poor ventilation, not enough light... Avoiding these and generally working on prevention had saved me from any real trouble so far.
The reason I have asked for a book was to have a quick and easy reference to help me to identify some problems that I can't currently relate to anything particular. It is far more efficient to look at some description and photos to identify a problem and if needed to dig further do discover all possible reasons, instead of taking pictures by myself, posting to forums and asking questions that have being answered hundreds of times probably.
For example I have Lagerstroemia indica plants and some of them are having some warts on their leaves as if the leaf is dusted with salt or more correctly like if salt crystals are protruding through their epidermis or maybe like some cysts filled with liquid, it is hard for me to describe it. Obviously I am lacking a basic knowledge in this area.
I had troubles with all possible pests on my Clianthus puniceus plants and I am tired of babying them so I am about do discontinue them. They are not dying, but are losing their good appearance and hardly ever get to flower. They are looking good enough for sale just for a short periods of time after intensive treatments with quite poisonous chemicals against spider mites, heavy pruning and heavy feeding to develop some new foliage...
I have some Aristolochias that show some browning of the lower leaves that I cant identify.
Nutritional deficiency related problems is another topic I need to know more about.
Otherwise everything grows as vigorously as it can, making my greenhouse to look ridiculously small... again.... :)
Currently I am growing more than 250 species of plants with widely varying cultural requirements - carnivorous, succulents, bulbs, shrubs, vines from all around the world. I am slowly heading to reducing this number and some specialization, but I will always want to try some new plant so it is unlikely that the number will drop significantly. Compared to my tiny space and not so good location this number is big.

No. 1: The Ortho Problem Solver. Nothing else comes close.

No. 2 (tie): Diseases of Trees and Shrubs, Sinclair, Lyon, and Johnson

No 2 (tie): Insects that Feed on Trees and Shrubs, Johnson and Lyon

There is nothing else that compares to the Ortho Problem Solver. Note: Get the one that when you look at the price tag, makes you gulp. they came out with a home problem solver, but you got what you paid for.

The Disease and Insect volumes are rather impressive in their own right, but they are written to be references, not light reading, with a focus on diagnostics, not control.

And then we get into the fun stuff, all the "buts" that people like to use to make their case special. BUT, I only use organic. BUT, this mentions sugar maple, and I have black maple. BUT...information is what you want, really. And the knowledge of how to use it. The info is easy. The rest is up to you.

From what you describe, I'd go with the ortho book. It has sections that deal with specific trees, shrubs, vegetables, annual, lawns, etc), but it also covers all the other things that can happen...from lightning strikes to lawn mowers, including environmental problems and nutritional stuff.

What I don't spend a lot of time on is tropical stuff. I have a few (ahem) houseplants, and I've caused a few traffic snarls due to obsessive rubber-necking during the summer, but I don't deal with a lot of finicky plants. There may very well be some very good references on tropicals, but when I look at my life north of the 40th parallel...not spending a lot of money on a book for plants from between the tropics, unless I can define a pressing need. Or win the lottery.

Thanks strobiculate!
I will, for many reasons, not use Ortho products. Do you think that in this case the 6-th edition from 2003 will be sufficient? Will the information on identifying, cultural practices and everything else aside from product recommendations differ substantially in order to justify the higher price of the 7-th edition from 2008?

We have the Ortho text as a reference here where I work and I find it mediocre at best. First, it does not address a whole host of plant problems that are common in my area and I would assume, elsewhere as well. Second, it tends to deal in non-specifics, like "root rot".........OMG!! There are dozens of root rots, some of which are of greater concern than others but there is no information on how to differentiate based on symptoms or other evidence. And finally the treatment suggested is entirely Ortho based. There is minimal information on alternative approaches or even cultural or biological control.

One can do so much better online.