There are two sides to the story mind you. Yes the cornstarch is keeping the weeds down. But it makes an excellent hiding place for slugs unless appropriate steps are taken.
The main problem is watering though. It does make watering more difficult. Not so bad in the winter when less water is required and it doesn’t evaporate but will be more of a problem in summer.
The ideal answer would be a seep hose system under the cornstarch. But as there is not the appropriate water pressure on the Go Local Food fields where the supply is gravity fed this is not possible.
It just goes to show that there is rarely if ever an idea solution that solves all the problems in any situation. But the poly tunnels are an essential part of our growing system, allowing us a longer growing season and the ability to grow a wider variety of crops to go in the crop share. So we persevere.