Critical stages for Downy Mildew attack on poppy opium is  humid climate.

in humid climat pathogen release zoospores which have the capability to increase the rate of disease propagation

Thank you for your replies, but I am interested to find particular growth stages in plant life. For instance; flowering stage, booting stage, hook stage etc.

You can find some information in this paper.

Thanks.

Why don't you read the book "The Downy Mildews - Springer

link.springer.com/chapter/10.1007%2F978-1-4684-3495-8_19

by EH Barnes - ‎1979. Similarly, Advances in Downy Mildew Research volumes published by Academic Press will also be useful.

Thanks!