If all methods fail and you haven’t been able to prevent or treat powdery mildew successfully, consider removing the entire plant.
An unhealthy plant is more susceptible to pests and other diseases.
A diseased plant can easily spread powdery mildew to other plants in the garden.
Remove the entire plant and do not compost it. Plant another fruit or vegetable in that spot that isn’t as susceptible to powdery mildew.