It's specifically used against slugs, not insects (maybe aphids) and fungus (and it certainly wouldn't do anything to the latter). Why dust the whole garden with it? Putting it around the plants susceptible to slugs would be a better option. And I find Sluggo far more effective and also an organic treatment (it's a mined form of iron phosphate).
I sure wouldn't use diatomaceous earth on lettuce or anything where the leaves are eaten - it's not all that good for people either.
I've never found it necessary to use an insecticide in vegetable gardens and that scatter it everywhere approach leaves me cold. You'd probably end up killing beneficials as well.

Laura,

i'm a fan of using diatomaceous earth for various purposes, but have a question about using it on plants.

What purposes exactly? Can you list them?

has anyone actually dusted their plants with it?

Absolutely. It's the number one method by which to utilize it if there is a problem with a particular pest that will specifically be affected diatomaceous earth. It can also be applied in a ring around the stem at the base of the plant.

My concern is that the de might dry the leaves out too much. I'm guessing that it might be good for the soil.

It doesn't suck moisture out of foliage. The sharp surfaces cut through the insect cuticle and the insect dies of dehydration.

there must be a reason that i've never heard gardeners using it for fungus and insects.

I don't know where you're getting your information but it's definitely used for certain insects.
1) dust a lot of it on the garden at night
2) water the foliage thoroughly the next day before the sun gets too hot.

Don't know where you're hearing your information. I only use it on foilage and occasionally around the stem. I would never use it as a soil additive.

You should never use anything in your entire garden for the sake of using it. This is the easiest way to kill off the good guys (beneficial insects) that eat the bad guys (pests). If you want to use it on plants, don't get any on the flowers. It'll slice up the few honeybees we have left. And I don't recommend incorporating mass quantities into the soil. Earthworms are good things: You don't want to hurt them until you put 'em on your fishhook.

Take the time to learn that there is not a "cure all" for every pest at every stage of it's life cycle. Some won't work if it's going to rain. Some don't work well if it's too hot, etc.

Pest management is complex, if you wish to use products, do so responsibly which goes further than reading the label. If you want to learn, a good place to start is here:

Integrated Pest Management
This lecture is presented in two parts. Each part is 90-minutes in length. Recorded in Sacramento County in California's Sacramento Valley, this lecture is byMary Louise Flint, Ph.D., Director, IPM Education and Publications, UC Statewide IPM Project and Extension Entomologist & Cooperative Extension Specialist.

Education:
B.S. Plant Science, University of California, Davis
Ph.D. Entomology, University of California, Berkeley

Appointment:
100% Cooperative Extension

Research Interests:
Integrated pest management of landscape, agricultural and garden pests; biological control of arthropod pests; alternatives to pesticides; adoption of alternative practices by practitioners; innovative delivery of pest management information.

Topics discussed in the Integrated Pest Management Lecture:

* IPM references and resources
* Preventing pest problems
* Natural common enemies
* Making less toxic pesticide choices
* Controlling aphids, scales, caterpillars, coddling moths, tree borers, snails and slugs, and lawn insects.

You can watch the programs now online:

Just make sure you have Real Player installed or download it free.

Integrated Pest Management Part1 90 minutes

Integrated Pest Management Part 2 90 minutes

You'll want to bookmark the following link to Professor Flint's Lab Research on:
Controlling Pests in Gardens and Landscapes: Vegetables and Melons

I promise you'll learn one or two things to put in your gardening bag of pest management arsenals.

;)

oldroser, you are somewhat misinformed about the DE. It is actually a very effective killer of large, hard-bodied insects. It works by percing the soft body tissue in between those hard, exoskeleton plates. It is also used extensively in animal feed, to control parasites in and outside the body (in animal waste). You can feed it to pets. It's used as a dust for poultry, as well as in their feed. You probably eat some every single day, as it is used to control insects in stored grain, used to make foods for human consumption.

I would never use DE without careful consideration, however. It is broad spectrum in its action, and harm could result in the population of pollinators, predators, and other beneficial insects.