Zucchini skin disease (holes)

Question

For several years now the zucchini in my amateur garden have always failed in the same way. The fruits start to grow but stay in an arrested development state (their size never goes beyond 12cm, the first photo below represents one of my largest ones) and their skin are punctured with small, superficial holes. The zucchinis also suffer from powdery mildew but that's harmless, right ? The garden is located in South France, in a place with plenty of sunshine and heat. Can anyone diagnose this or suggest anything ?

Update : since some answerers asked, to fertilize I used some horse manure that I buried before putting the plants (note that this is an organic farming question as indicated by the tag below).

Answer 1

We need to know about the fertilizer you've used, when you used it, how much. Zucchini usually do TOO well. Powdery mildew is rampant. Best to chose varieties that have some resistance. And, Bamboo taught me this 'trick': mix one part milk to 9 parts water and spray the leaves of your tomatoes, your squash, cucumbers...This really reduces powdery mildew. Which most certainly ruins your harvests.

This looks like rodents to me...see the little teeth marks? My favorite way to boost harmony is to feed the rodents somewhere else far away. Or adopt some feral cats that are fixed. Don't use DeCon or traps. Kill mice and the tide will come right back. I've had slugs but never had them eat my fruits. Mice and rats, now that I've had. This looks like tiny little mice. Rats would have eaten far more.

Row cover would be another avenue that I am finding more and more uses for and finding how the heck did I garden without it? You could cover your plants and staple, bury the edges in the ground. I would also go out at night verwy verwy quietly with a flash light. If it is slugs, you'll see them. Take a pair of scissors with you to cut in half. Kindest way to minimize slugs. If you've got a lawn, take your scissors and flashlight. Slugs LOVE to come out on the lawn, it is weird. I hate killing anything but this is the most 'humane' way and you only need to do it a few nights to make a huge difference in your slug population.

Answer 2

It's possible that your plant doesn't have enough available potassium.

Potassium is important both for fruit size and for added strength against pests/diseases. Silica and calcium are also helpful for strengthening plants. Potassium is also helpful for increased heat and drought tolerance, and for water absorption. It's good for roots, too.

I'm curious about your fertilizer ratio. Potassium is the K in NPK (so, it's the third number; even if you've been fertilizing, if the N is too much higher, it might be overpowering the potassium). Some fertilizers may have incompatible ingredients, too (which may make some of the nutrients unavailable). So, do your research, look at the ingredients, and be careful.

You could just give it some wood ash for potassium/calcium, though (not too much at a time). Maybe put a handful or two of wood ash around the plant (and water it in). Otherwise, the form of potassium I would recommend is potassium sulfate. It has a lower salt index than potassium chloride, and it shouldn't kill the soil microbes like potassium chloride.