Hi: looking at the leaves in your photos, it doesn’t look like the plant is suffering from a viral disease, which can be a cause of the interveinal chlorosis that you’ve described. So in the absence of viral symptoms that would include leaf mosaic/mottling and leaf deformities, I suspect that your zucchini is suffering from a nutritional deficiency. The plant(s) showing yellowing between the veins that progresses to leaves turning brown could be deficient in potassium, iron or magnesium. I’m going to reassign your question to the horticulture specialist who has experience in vegetable production to weigh in in your options.

Damage appears to be on older leaves, which is not uncommon. The dry edges are not a problem. The newer leaves seem fine. Remove the affected leaves and make an application of fish emulsion.

This looks like a nutrient deficiency, and based on the interveinal chlorosis (green veins loss of color in leaf) likely a problem with uptake of magnesium. A soil pH that is too high or too low can prevent plants from taking up the water and nutrients that they require. Zucchini like a soil on the acid side, between 6.0 and 6.5. You can get a simple pH test kit from a nursery to quickly assess this, though these tests are not always accurate you can get a good idea.

Thank you!  I was researching where to get one of those little kits last night. I’ll go pick one up after work today. I appreciate the advice!