[Zyg]

Can anyone tell me what is wrong with my sunflowers pleas?
The leaves are swollen and solid, and no flowers are forming.

[Yorkie]

That is very weird 

Any chance of herbicide damage?

[Zyg]

I wondered that but the only possibility is that when I planted them, I planted them with a lot of organic compost. This compost is made locally from collected manure. It is properly treated etc. but I wondered if the manure comes from fields that are treated for weeds?

[BabbyAnn]

It may be aminopyralid - it was initially withdrawn from sale because of contaminated manure and the effect it had on gardens, and then re-introduced a few years back.  It's a very persistent broad leafed weedkiller that can find its way into manure via the feed and bedding, and can take a number of years to degrade - the manure needs to be turned over regularly to let soil bacteria break it down.

[Zyg]

Ok. Thanks. I have several sacks left.  Now I don't know what to do with it. 

[Yorkie]

Ok. Thanks. I have several sacks left.  Now I don't know what to do with it. 

If you go onto the main website (click Allotment Garden at the left of the top main banner) and enter aminopyralid in the search box on the top right of that page, you'll find a lot of articles written the site owner John.

One of them shows how to test whether the manure is in fact contaminated; suggest you try that to know for sure.
http://allotment-garden.org/garden-diary/321/testing-for-aminopyralid-in-manure/