3.8 Fungicides in general and for damping off

>I need help identifying a whitish fuzz that's causing our rosemaries to shrivel and die back. Then I need help figuring out what to do about it. I have tried washing it off, but it keeps returning within a week. One of the big ones seems to have died completely from this already, the others have mostly only new growth left alive. Is it possible that the fuzzy mildew from our neighbor's grape vines could have taken hold on rosemary?

From: Joyce Schillen gardenpg.cdsnet.net:
What you describe certainly sounds like a fungus, of which powdery mildew is one. A very good fungicide is 3 tablespoons baking soda, 2 ½ tablespoons horticultural oil (also called ultrafine oil or summer spray oil) and ½ teaspoon liquid soap mixed in a gallon of water. Spray all surfaces about every ten days. This has been tested extensively by Cornell U. for black spot on roses, and in Israel for powdery mildew on squashes. Some plants are sensitive to the oil, so test it on a small section first to make sure there's no phytotoxicity.

Another good fungicide is strong chamomile tea. This works great on damping off disease in seedlings:
Pour 1 cup boiling water over ¼ cup chamomile blossoms and let steep until cool. Then strain into a spray bottle. Spray on seedlings AND soil whenever evidence of damping off disease or other fungus appears.
I swear, this is nearly magical. I've seen it completely knock down that white cottony growth that shows up on soil surfaces and makes seedlings keel over and die. The tea only keeps a week or so before turning rancid, so that's why I make such small quantities.

From: Kathryn M. Bensinger kbensin.MAIL.STATE.TN.US:
What you will find inside any plant suffering from fungus is the vegetative body know as mycelium. What you see above the stem surface is actually the fruiting body of the fungus. The mushrooms you eat are just the fruiting body, the rest of the "plant" is below ground. If you slice open a twig or stem of an infected plant (dying or dead) and find squiggley line which resemble threads or fine root hairs, you have fungus. Most mycelium is whitish or tannish but may be other colors depending on which fungus; one toadstool has blood red!

Both vinegar and baking soda will work by altering the pH of the plants surface; one to very acid, the other to very alkaline. This allows the plants natural resistance with an edge so it can throw off the fungus. Baking soda is used most often with powdery mildew because this fungus likes cool, humid, acidic environments. It works best before the "powder" shows. Here in TN the summers are always so humid it feels like you could wring the air and I spray my bergamont and other suseptible plants with baking soda/ water mix once a week from before any sign of fungus til humidity levels drop (about the end of June til end of Sept). It works.

Vinegar works everywhere baking soda doesn't - this is my choice when I don't know which fungus I'm dealing with.

Healthy plants never get fungus. Too much fertilizer causing too lush growth, light conditions which are low and (plants get leggy), night temperatures that are too cool or too hot, and (especially in winter)waterlogged soil due to poor drainage, etc. are all stress which weaken the plant and allow fungus the opportunity to move in.