Question
I used a brand of organic corn weed/feed fertilizer prior to seeding my dog run (grass) - it has been very humid and rainy for several days. Now the area is covered with a white fuzzy-looking growth (mold?)...what is it, what do I do about it? I thought the rain would be good (it said on the bag to water well after applying and Mother Nature helped me out there....Help? Should I be concerned? I am keeping my dogs out of there right now - should I rake it all out or will they send spores everywhere? I can't use chemicals due to our being a "well-neigborhood" (all shallow) - we have to be very careful.

Answer
Rule Number One: Never use ANY kind of Weedkiller, organic or otherwise, prior to sowing Seeds of something else you want to grow.

Because the Weedkiller, including organic weedkiller, will kill everything in sight.

Remember that.

Odds are, you applied your 'weed/feed fertilizer' too late for it to interrupt Weeds growth.  Since is it Corn-based (which is EXCELLENT, because it generates slow release Nitrogen ALL SUMMER LONG), it probably became prone to mold growth with the thick, highly humid conditions you have been dealing with.  But I don't think this is anything to worry about.

Consider this:  If you toss a wet towel on the bathroom floor, it gets Mildew, right?

Do you stay up late at nights worrying about this?  Of course not!  There's nothing to worry about.  Keep the towels off the floor, and they won't get Mildew.

If you walk into the Living Room, do you notice Mildew all over the sofa?  Of course not!  The Sofa is fine.  It's Sunny, and it's dry.  No Mildew spore is going to get through a dry, Sunny day on a sofa.

Let's take Algae.  If you put a vase of flowers on the table, and keep the water, what are the odds you will have a green coating on the inside of the glass in a week?  Two weeks?

But if you change the water daily, the algae never gets off the ground.

What's up with that?

Fact is, there are microbes everywhere.  We are breathing them right now.  But they're not a problem here.  And they're not a problem down on your Dog run or your Lawn.  Just keep them dry.  The dogs will be fine.

Your followups welcome.