Root lodging vs stalk lodging

​2018 harvest in US Corn belt is showing some lodging problems.  Analysis of cause(s) should begin with distinguishing between what is called root lodging and that named as stalk lodging.
 
Root lodging generally occurs anytime during the growing season when the lateral roots of the plant are insufficient to avoid the plant leaning when faced with winds.  This vulnerability can be associated by feeding on roots by insects, soil texture or moisture inhibiting growth of the lateral roots or simply inherited tendencies for deeper ‘taproot’ that may be a favorable character for reaching water during drought conditions but a disadvantage if water soaking in upper soil softens the soil.  If root lodging occurred before flowering, geotropism will cause new growth to result in curved plants.  These plants and those that root lodged later in the season usually maintain green, lower unbroken stalks.  Pre-flowering lodging may cause incomplete pollination and therefore reduced grain yield and later lodging may complicate harvest.
 
Stalk lodging has different causes and symptoms than root lodging. Symptoms of stalk lodging begins about 15 days before kernel abscission layer (black layer) forms. Causes involve the supply and translocation of carbohydrates to the roots, stalk and grain.  Nearly always, root tissue death causes the plant to wilt because insufficient water is absorbed from the soil to meet the water loss from transpiration in leaves.  Wilt causes cell death in all tissue including the stalk.  Dessication of the stalk pith cells causes withdrawal from the outer rind, reducing the stalk strength. Various fungi invade and further weaken the rind tissue.  Late season wind now can cause the stalk to break at the lower internodes.  Early wilt results in stoppage of translocation of sugars to the grain and therefore light grain density.  Broken stalks maybe difficult to harvest.  
 
Inspection of the stalks before harvest can discern the difference between root lodging and stalk lodging.  Lower internodes of root lodged plants will be green whereas stalk lodged plants will have brown outer rind color in the lower internodes.  Genetics involved in these two types of lodging are different. Root lodging involves genetics affecting root type of growth whereas stalk lodging genetics involve factors affecting photosynthesis and sugar translocation factors including multiple plant biology interactions. A deep-rooted hybrid may be favored in drought seasons because it reached water, favoring silk extension and therefor more kernels than the hybrid with more lateral roots towards the soil surface. The latter may suffer with fewer kernels because of silk extension missing pollen.  On the other hand, if the late season is unfavorable for photosynthesis, the deep-rooted hybrid could be vulnerable to stalk lodging.