Throughout the growing season, from the point of planting through to harvest and dormancy, fruits, vegetables, and other horticulture crops have high and specific water requirements. Generally, most vegetables benefit from the application of an inch (2.5cm) of water per week, whether through natural rainfall or irrigation. Plants can make do with less, however yields and quality may suffer, depending on the crop.
As the growing season draws to a close, the water requirements of crops changes, with some continuing to need regular water up until freeze up, whereas others need to have the tap turned off well in advance.
In late summer, actively growing crops will still require moisture. This would include crops like day neutral strawberries, raspberries, as well as most vegetables. The amount of water will vary, but it may be a bit less than in the peak of summer, with high temperatures, dry, windy conditions, and rapid plant growth. Crops that are actively fruiting, such as the strawberries, will need water right up until the crop is done. Younger crops, such as crops that were late planted and are still actively growing and maturing, will require water at similar levels to other times of year. Other crops might need to be gradually weaned off in late August, depending on when they are due to mature. The water requirements will vary with the age and maturity of the crop.
Any crops that need to dry down to firm up their tissues to be able to store for extended periods should have water levels dropped back once they show signs of starting to mature. This might include onions starting to have the tops fall over, or perhaps crops like potatoes, which start to die down.
Other crops, such as June bearing strawberries, should get a solid top up of moisture prior to freeze up, as a part of the renovation process. Perennial woody trees and shrubs, whether deciduous or coniferous, should get a good drink of water in late summer and early fall, to ensure that they enter dormancy well hydrated.
Some crops will continue to grow if moisture is plentiful, which can put them at risk of delayed dormancy and winter injury. Crops like apples should have the application of water cut back in mid-August, as much as possible. In general, bush fruit should have the water application rates scaled back starting in mid- to late August, to encourage dormancy.
Keep in mind that in late summer, there are typically bigger differences between day and night temperatures, which can lead to longer leaf wetness periods, heavier dews, and potentially greater risk of diseases.
As with all recommendations and guidelines, they are subject to the foibles and complexities that nature likes to throw into the mix. You can only control what you apply. While long range forecasts can be as useful in the short term as sunglasses at midnight, they can shed some light on the general conditions that might be expected (e.g. cool, wet fall, or hot and dry – that sort of thing), and you might make some decisions based on that.