I've been watching the local arable fields and guessing the crops. Mostly wheat, wheat, wheat, and....more wheat. But there's also this:
Oil seed rape coming into flower, about half a mile from home as the bee flies. Wish my bees were here to take advantage! Oil seed rape gives a pale, set honey. Not the best for comb honey sections, but very popular in jars.
Speaking of crops, I've signed up to BeeConnected, a notification system through which farmers can warn beekeepers of their intention to spray local fields.
I've added the location of my apiary so that I'm set up to receive notifications. If the notified spraying time window is sufficiently precise, the bees can be shut in to prevent foraging during that time. E.g., Farmer intends to spray a crop with insecticide between 6 - 8 am on Monday within 3 km of Copper Bee Apiary => Beekeeper closes hive doors at Copper Bee Apiary at 10 pm on Sunday and re-opens hive doors at 10 am on Monday. The bees can't be shut in for long, but at least they can be kept in during the peak time for poisoning risk.
As shown on the screen shot below, it doesn't appear that any registered farmers are currently planning to spray insecticide in the fields within the alert radius of my apiary. Registration with the system is voluntary, and the local farmers may not be registered. But the system seems a good idea anyway.
Update 8 May 2018
I received an e-mail notification from BeeConnected about a planned spraying:
The website informed me that lambda-cyhalothrin is to be sprayed on oil seed rape within 4 km of Copper Bee Apiary.
That's further away than the oil seed rape field I was writing about, and hopefully that local one isn't being sprayed, but who knows. If there's closer oil seed rape, maybe my bees won't fly to the distant oil seed rape where the spraying is. I considered shutting them in, but in this baking hot weather that would probably do more harm than good. And I don't know how long I'd need to keep them in for - how long does that toxin stay on the plants? Maybe weeks! So I'm taking the view that 4 km away is far enough away. But I'll be vigilant for signs of poisoning in the week to come.