I've a garden that I try not to water too often, if it is really hot and dry then I will water 2 or 3 times a week, but other than that, I let them be. They grow well, but there are a lot of fungal diseases that occur, at least partly because the plot has been used as a garden for many years, and I can't move it.
Primarily tomato blight and powdery mildew on the cucurbits. I know that the blight is from splashing, and plastic under the tomatoes has gone a long way to controlling that. Other than spraying, I don't know what can be done about the mildew on the pumkins.

Then I visited my sister's garden, and everything that she had there was almost 2x the size (not necessaryily 2x productive, but more so than mine). She has automatic watering which she has water for 20 minutes 2x a day (40 minutes per day total). No visual signs of disease, she also has a spot not used before for a garden.

I was thinking that that much water would cause the funguses to spread since they like it moist, but then I thought that more water would result in stronger plants which could fight it off better.

Would I be better off watering more often (as in automatic) or would this cause more problems than it would solve?

thanks