R. A. Neve wrote a book back in 1991 titled 'Hops". it covers stuff like botany, production, pests, breeding and varieties. different types of research work done throughout the major hop growing regions of the world is cited throughout. i bought it through the AHA brewers' publication series back in the early 90's but i don't think it's being printed any more (Chapman and Hall). many new varieties being grown since then, but not many of the basics have changed. a wealth of information if you can find a copy.