In essence the type of analysis will (and should) depend on your response variable. Therefore please give some more information on how you measured the proportion infected. Tell us what the response variable is in its essence.
E.g. Did you do this via digital photography (= number of pixels infected) , via grid count (n grids) or was it a guestimate?
In short however I can tell you that poisson is not appropriate. Not if your variable is bounded by an upper limit (100%.