Strawberries are easy to grow and their fruit is not. Planted tight, watered from above and left sitting on bare soil, a good part of the harvest goes to mould. Most of the trouble starts in the moisture around the plant rather than in the plant itself.
Likely cause
Grey mould: the classic strawberry loss. The spores are everywhere already; what decides it is whether the fruit stays wet.
Likely cause
Powdery mildew. It comes with crowded planting and, unlike grey mould, does not need wetness: it spreads in dry air too.
Likely cause
Leaf spot. It will not end the harvest by itself, but it takes leaf area and the fruit comes out smaller.
Likely cause
Slugs or snails. They feed at night, so the damage is visible and the cause is not.
Don't confuse it with
Easy to tell from bird damage: a bird leaves a clean, sharp beak mark, a slug leaves a ragged hole and a shiny trail.
Likely cause
Spider mites. They take off in hot, dry air, especially under cover.
Answering one photo is the easy part. With Strawberry, whether the advice worked only shows days later, which is why Farmagile comes back and asks.
With strawberries the result of any change shows in the next batch, not the current one: mouldy fruit does not recover, and the fix worked if the following flush stays clean. Which means the answer to 'did it work' only exists a week or two later.
No account needed. You see the answer first.
This page is general information, written without seeing your plant. There are deliberately no product names and no doses: both depend on the plant, the region and the season, and a guessed dose on something you eat cannot be taken back.