There is no universal blight, but there are blights that affect related plants and some that affect non related plants.

Potatos and tomatos are both susceptible to the same fungal species (blight), but I wouldn't think your cukes and zukes have the same fungal pathogen.

Unfortunately fungal pathogens are really difficult to control once they develop and much easier to prevent.

Overhead watering and rain favor blight. We can't control the rain, but overhead sprinklers are always a mistake in the home garden where fungal problems are likely.

Mulching to prevent soil splash can also help as the spores will be forever in the soil.

If you have a fungal problem on a plant regularly then it's worthwhile to use a fungicide as a preventative all season long rather than wait for it to take hold and then desperately (and often futilely) try to get rid of it.

A good, organic, safe, university proven home/organic fungicide is 1 gallon of water with 1 rounded tablespoon of baking soda. Many, myself included prefer to add 1 ounce of oil to the mix. I prefer using neem oil as it has messes up insects that feed on the sprayed plants (but doesn't usually affect insects that just crawl over it), however those wishing to avoid the insecticidal effects can also use canola oil in the same amount (1 ounce per gallon of water).

The baking soda kills fungal spores and the oil helps prevent spores from attaching to the plant and may smother existing ones as well. Do not use oils in the heat of the day on any plant, apply in the evening when the sun is low in the sky.

Apply every couple weeks throughout the season and more often in humid or wet weather. I would apply it after every rainfall since that's when the fungal spores start taking hold most easily.

conditions that encourage one pathogen encourage others as well

That about covers it all. Weather we can't control but in addition all the good above info from justaguy, there is a long thread over on the tomato forum called "my blight fight" that you might want to review. It offers several good links to additional info and control recommendations.

I wish you luck.

Dave