For the stalk discoloration, it's hard to guess from the single cross-section.
Maybe Phytophthora: http://www.ipmimages.org/browse/subthumb.cfm?sub=6955&area=62
Maybe tobacco wireworm: http://www.ipmimages.org/browse/subthumb.cfm?sub=6902&area=62
Do a longitudinal slice of a discolored stalk. Also look for a pinhole in the stalk. Pulling up the roots may reveal additional signs. Then cruise through the ipm images: http://www.ipmimages.org/browse/AreaSubs.cfm?area=62.
Bob
Maybe Phytophthora: http://www.ipmimages.org/browse/subthumb.cfm?sub=6955&area=62
Maybe tobacco wireworm: http://www.ipmimages.org/browse/subthumb.cfm?sub=6902&area=62
Do a longitudinal slice of a discolored stalk. Also look for a pinhole in the stalk. Pulling up the roots may reveal additional signs. Then cruise through the ipm images: http://www.ipmimages.org/browse/AreaSubs.cfm?area=62.
Bob