Your fruits did not get pollinated. The plant only grows fruit to supply seed to assure future propagation. If the fruit does not have any seed the fruit will not grow and it dies.

I hand pollinate so I am not sure what is going on. I take the male flower, tear of the petals, and use the stamen(?) and rub it all over the the inside of the female flower.

Am i doing this correct?

Kimmsr is right. Those fruit were not pollinated. Sometimes temperature extremes can affect the potency of the pollen. Have you had unusual weather lately?

Your plants are beautiful and healthy and you appear to be a good gardener, so forgive me if this question is insulting. Many people I know cannot tell the male from the female flower and sometimes have problems differentiating between them. Also, are you seeing the actual powdery pollen? Can you rub it off on your hand? It won't do any good to try to pollinate with a male flower if it isn't at the stage where the pollen is ready and viable.

Are the male flowers the ones on the tall stems? So we can hand-pollinate when the fruits are tiny?

The male flowers will be the ones that do not have a bulbous growth, the ovary and what becomes the fruit, behind the flower. To be sure of pollination the Stamens in the male flower must make contact with the Pistals in the female flower. Usually that is easily done just waggaling the male flower in the female flower blossom.

I have zucchini growing much larger and then rotting from the tip and getting shriveled up just like in the picture. They are definitely fertilized. I have dissected a few of them. While some look soaked inside, others have rots making it pulpy and hollow inside. Any idea what it could be? In the same plant there are other zucchinis (mostly those that are off the ground) are fine.

Alm99 - did you ever figure out your issue? I'm currently having the same problem. The only thing I can figure is our extremely hot and humid weather and the pollen on a couple male flowers not looking normal. I might try with younger male flowers that haven't been in the sun so long.

Any help is greatly appreciated.

I have very similar problems with my squashes. I know it isnt due to lack of pollination because the fruits are not even big enough for that.they are about the size of finger nail clippings and are already turning yellow. The problem you have I agree, it is most probably insufficient pollination, You prob need to make sure all the stamens have pollen on them.

as for my problem I know it isnt lack of fertilisers. anyone has this problem. thanks

did anyone have a solution for this?
I have the same problem.
The fruit are not yet mature enough to be pollinated, as in the female flower has not turned yellow and opened. The fruit looks healthy and then suddenly yellows and shrivels.
I did also have some blossom end rot on my Zucchini but it looked different to this and I believe I have solved that issue. thanks

I had this problem all the time. I could never find an answer either. It certainly didn't seem a lack of pollination. I'd get those early abortions, where the female flower didn't even get to bloom before yellowing and dropping off.

I'd also get the ones that yellowed and dropped off after pollination. And I know for fact they were pollenated because I even took the anthers of a male flower (and sometimes even from a different plant of the same species), broke them off and forced (aka raped) the flower by placing a fully pollen loaded anther on the stigmas. I even tried this in the morning. But still....a good number of them aborted.

Without any references to turn to, I came to some very likely theories (which I believe very possible anyway)

1. The plant isn't big enough. I may think it is, but the plant may not be ready.

2. Not enough total male flowers have opened in the plant's lifespan? (like the plant keeps count???)

3. Not enough light??? I had significantly more squash abortions in a part shade/part sun spot in my grandma's yard than the last year when I planted in a sunnier spot.
- Even still I had a great number of abortions earlier in the season until the vine got gigantic. (point #1 may be in effect)

5. Plant's own health? I noticed later in the year as the squash vine borers took ahold of the plant, there were a lot more abortions. Especially true with zucchini. The plant might look healthy, but if that one branch had a larva feeding inside it, then the first sign of death would be a lack of blooming female flowers and even more rare ones that produced squash.

6. The weather. More specifically night time temps. It may be the night time low temps have to be under a certain temp. I noticed no matter how early I planted or how large a vine I got to grow indoors before planting,there was always a dearth of mature squash (specially winter varieties) in mid July. This would be true even with the one spring in 2011 when I got a squash growing in June. It almost never failed. As long as the lows didn't drop into the lower 70's for summer squash or 60's for winter types, I could forget having any new female flowers for that week. I'm guessing lows of 80's kills the pollen or the flowers??? Idk. But as soon as the low temps cooled down in the 70 or 60 range, then I'd get a successful pollenated and developing squash.

Right now I believe out of those points #1 and #6 are the most likely. I just wish I could find more scientific evidence to back up my theory.

Thank you so much for your suggestions.
I think in my case #1 and #3 may be the contributing factors. It is a new garden bed and I was concerned there may not be enough full sunlight hours. It is approaching summer here and as the sun is getting higher in the sky the garden is actually receiving less direct sun due to the position of surrounding trees. The new leaves are not nearly as big as the original ones which makes me think the plants may not be getting enough energy. They are putting out so much potential fruit it is disheartening when they don't mature. Thanks Again Fieldofflowers.

These would be my 3 main hypothesis if this were my case:

1.- A Young plant. The first flowering are one sex flowers, mainly males, so pollination is rare.
2A.- Bad pollination. Atract more bees by putting flowers close by the bed or do it manualy.
2B.- There are asyncronic blosom between male and female. You may have flowers buy not both mature and open at the same time.
3.- Bad seeds. Maybe the plant has some genetic defect.

I think fieldoflowers is onto something and I am going to monitor for those same things.

I have a number of healthy butternuts growing on my vines and good soil. New females though are aborting left and right when the bud is tiny. (no bigger than a pencil eraser).

I realize this is older post but when I called my extension agent I got the same old "not pollinated" story even though the bud was nowhere near blooming before it died.

I have notice the past few weeks we had some real heat even though it was only in the low 90s it felt hotter....and the eggplants and okra are the only ones thriving. It is almost too much sun for my tomatoes.