One of the old collapsed raised beds in our allotment garden has a large volunteer squash plant growing in it. The plant is very vigorous and has large leaves with some white markings and a few developing squash fruits that are shaped like a butternut squash. The largest fruit is currently about 8" long a pale greenish yellow with faint green stripes. When it was younger it was light green with pronounced darker green stripes. Are all (or some) butternut squash striped when young, or is this likely some kind of hybrid squash? Although it is a huge plan with lots of flowers there seem to be very few fruit (only 3 or 4). Is there anything I can do to improve the fruiting, or is it too late for this year? Sorry, I thought I had a photo, but can't find it.
We had the second night frost this autumn tonight (the first was on August 31), therefore I collected some of my butternut squashes. I have two different cultivars, from different seed sources, one with significantly smaller fruits than the other, but both variants are slightly stripy.
You can improve productivity by keeping bees or promoting bumblebees in your garden. Butternut squash is more warmth demanding than common squash, so maybe it's too late for current year. My plants have provided so far 3 squashes per plant, and at least another 3 per plant are still ripening. They start producing later than common squash, so maybe earlier sowing would also let the harvest to be more substantial.
I suppose what you call a "volunteer plant" is one that you didn't plant, or that self-sowed ? The seeds of some varieties of squash are not stable, and can hybridize. I planted what we call here "patidoux" a couple of years ago. The following year, I planted seeds from some of the fruit I picked, and a few of them were slightly different, rather shaped like butternut than "patidou". They're even tastier and more delicate than butternut. Here is a site in French with a photo of "patidou" : Potager City Here is another site where you can see many photos of different varieties of squash. For instance "Honeyboat Delicata" seems to look a bit like your description though no size is mentioned : Les variétés de courges - Description