What can be done about plant diseases?

Infected leaves and fruit (looks burnt!)

After my post up-dating the fact that I actually started the garden and its progress, a friend ask if I was having problems with diseases on my cucumbers and what I was doing to treat it.

Infected squash leaves

While my garden looks nice and lush in the post from two weeks ago, there were a bunch of leaves that had powdery mildew on them. And since that post, there still is a bunch of powdery mildew on my squash and cucumber plants. I really hate the idea of just getting rid of the entire plant all together, so I do my best to treat the disease as best as I can. When I searched and asked about eliminating the fungus, there did not seem to be any fail safe method other than getting disease resistant plants. Powdery mildew is one disease that is a common problem and persists as long as there are hot days and relatively cool nights (humidity doesn't seem to be an issue).

Last year, when I had a problem with blight on my tomatoes, I used a copper based fungicide that is approved for organic gardening (which I try to use whenever possible). However, the copper fungicide is not something that you're really supposed to use when the plants are fruiting (oh and it's not really effective against the powdery mildew I have this year). 

Blight on last years tomatoes (above)

Removed infected leaves and fruit

Neem oil (below)

The local garden center (Merrifield Garden Center) recommended neem oil. It doesn't eradicate the fungus but it seems to kill of some of it and at least slow it down.  You have to make sure your plants are really well watered before you apply it. I was warned several times when buying the bottle that it could burn the plants if they were not well hydrated. And it can only be applied every 5-7 days, so diligent treatment is a must.

Other things that I have done, removed yellowed/dying leaves and fruits. This seems to help, especially since gray/brown leaves will probably be covered in spores, which only spreads the fungus. A bunch of the websites sites that I read suggested that the more air movement there is among the plants is also helpful in preventing fungal spread. After removing the leaves, they should go directly in the trash and not be composted.

There are a few methods that I haven't tried yet. One is sulfur dust or spray, the biggest earning is (again) burning the plants. I didn't seem to be able to locate any at the Home Deport or the garden centers, so I might have to order it on Amazon. The other method that Growing a Greener World and Growing Real Food have mentioned is spraying the plants with diluted milk. It sounds very interesting and would be a bit more economical than ordering sulfur dust, so I will probably try that method next.

Regardless of the diseases the plants have, I've been able to harvest cucumbers and squash.