In article ,
Player1 wrote:

Planted some popcorn a month ago and now the plants have 4-5 leaves.
They are tall and weak - most of them have one leaf that has broken
near the stem but is still alive - all those leaves have some white
dust like substance in the thing in the middle of the leaf that
supports it. Also, all but the newest leaves are going brown at the
tips - lower ones the most.

Some pictures:
Plant 1 - http://tinyurl.com/3nnt99
http://tinyurl.com/4jxje8
Plant 2 - http://tinyurl.com/44sobp

The window faces south-west. Fertilized it once, with the one you mix
in the water, didn't help though. May the problem be the cold air from
the window that is open very-very little all the time (0-15 degrees
celsius outside), sunburn (about 6 hours of direct sunlight on the
plants on cloudless days), saltburn, over-watering or something else?

http://vegetablemdonline.ppath.corne...t%20Corn/CornR
ust/CornRustPhotoList.htm

Can it be one of these?

Bill

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Garden in shade zone 5 S Jersey USA