Green corn stalks
Corn plants that did not produce more grain than could be supported by sugars stored in the stalk pith tissue and post-pollination photosynthesis, finish the season with slowly senescing leaves and green outer rind tissue. Enough roots of these plants remain alive to ward off potential invading fungi until the temperatures in temperate zones become low enough to slow growth of these microbes as well.
After black layer forms in the grain, there is little competition for carbohydrates among remaining living, but ageing, cells in the corn plant. Almost all plants that make it 60 days after pollination with green stalks will be standing until harvest. Pith tissue in these stalks will remain attached to the outer rind cells with the structural strength of a rod.
Plants that committed to more grain fill than photosynthesis could fulfill will have brown lower stalk color. This began with a wilt symptom because the roots, deprived of enough carbohydrate to support life in their cells were invaded by microbes. Eventually this reduced water uptake to a point that the plant was losing more water through stomates in leaves than could be met. These plants showed the wilt by all leaves turning gray and then brown. The stalk color turned from green to yellow and finally brown as well. Inside the stalk, the pith tissue collapsed away from the rind, changing the structure dynamics from a rod to a tube. This essentially reduced the strength in these plants by one third. One can judge the vulnerability to lodging percentage in a field by looking at the lower stalk color in a field or in variety plots a few weeks after black layer. Those with brown stalks will be easily broken with a nudge from the hand as well.
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About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.