You need to go along with your specific conditions. Watch your plants and gradually experience will tell you when they are not worth keeping any longer. If you get frost the zucchini plant will die. Without frost just wait until no more are produced, unless you need the space. In my climate the plants sometimes start to rot from rain and lack of sunshine before the first frost.

In Southern California we have a longer zuchini season than any other part of the country. I've picked zuchini here in San Diego in December. So long as your plants are putting out new leaves and blossoms you can keep picking. Just keep an eye on the central stem. If it begins to go soft you have about used the plant up.

My zucchini produces until the plant freezes. It still produces after just enough frost to kill the tips of the leaves, but it doesn't take much cold to kill zucchini.

I wouldn't know about that. Being from Georgia, my Zucchini is done when the SVB kills it.

you are better off starting new seeds rather than trying to keep an old plant going. Plants die of old age just like people. Young plants produce better just like people.

If you start new plants in pots you will save a lot of grow time in the garden when you switch to new young plants.

for me, I move on to other plants. But then my grow season is very short.

I never spray anything. I allow nature to take its course. Zuchinni are not long lived in my area.

Not sure which zone 9 you are growing in, but Sunset Zoning seems a bit more defined for planting - especially in So. Cal, with the many microclimates.

So - I like to recommend to my local vegetable gardeners, the seed planting schedule on the web - www.digitalseed.com. Then scroll to their vegetable planting times. This applies mainly to near San Diego gardeners, however.

On that schedule you will see the "winter zucchini" planting times at September/October. I planted some zucchini using the seed packet recommendations - which were earlier. The poor zuke shivered through almost 3-1/2 months of overcast weather - producing nothing. I was about to pull it, then the sun came out, earlier this month, and it began to produce like crazy.

If your plant looks healthy, putting out female blossoms, I'd say leave it in. I think "winter zucchini" is more productive in our zone, than anywhere else.

Just my 2 c's.

Bejay