The end of it has started to rot? I've never had this happen to squash before, the plant looks great.

Frilly, I've had that happen before - I think it's from lack of pollination.

Concur: usually it is from lack of pollination. Some times if the plant is stressed it will abort excess fruits. Plants sense how many fruits they can bring to maturity. After all from their point of view, their sole purpose is to reproduce.

This was the only fruit it had at that time, it was about 4-5 inches long when it started rotting, it was sitting on the soil so I thought maybe that was why. Also been really humid here w frequent daily rains. The plant itself is huge, wondering if the soil has too much nitrogen?

My yellow squash has had a few failed fruits and I was not surprised- assumed lack of pollination on mine, too. . In my case, I could see those were in weird positions and likely the flower couldn't even open very well-- plus, the plant is loaded with females and not many males.

I don't think you can do much in case of too much nitrogen except, don't add any more.

well we just put the beds together last summer and added alot of compost so just guessing maybe rich in nitrogen right now. It has been a crazy year for the weather of course too, I got them planted way too late cause it kept raining and we had low night time temps until the end of June. It just didn't warm up. Then we got like 3 weeks of mid 90s which we usually don't get until July, I don't think anything knows what to do this year!

Just because one squash is going bad doesn't mean the others will - your plant will probably be fine (it certainly looks healthy enough!)

Concur. It is common for the first squash to abort, especially among the modern hybrids, which tend to send the females out ahead of the males. Many of these varieties are BIG plants. This is Mabel, a producing machine, but the first females aborted because there were no males to use for hand pollination. It is now now huge and still producing even with a pickle worm invasion.

Okay guys, thank you! That was helpful!