My zucchini plant grows beautifully. I am getting fruit now (this has happened before). The stem from the ground up starts to turn black. I see no bugs.
Certified GKH Gardening Expert
This may be a fungus of some kind.
You mention that you have seen this issue in past years. Crop rotation is important to help control fungus issues that reside in the soil.
You can use Neem OIl as it does work as both an insecticide and fungicide.
Here are some links for you.