Corn and pre-flowering rain

​Water has many effects on the early growth of corn.  Cell elongation in roots and leaves is the main contributor to expanding root volume and plant height during the first two months after planting.  Cell elongation in young cells occurs as water moves via osmosis through cell membranes, expanding the cells before cell wall solidification occurs.  Much of the plant upward growth witnessed during this time is from elongation of cells in the leaf sheaths. 
 
Water supplied to plants during early pre-flowering stage affects plant height.  As the apical meristem later begins to expand into producing more stem tissue cells, water has the same interaction ultimately determining how tall the corn canopy will be during the post-flowering period.
 
Rain in the early season also affects corn disease development for the season.  Many potential pathogens survive in the previous seasons corn debris.  Moisture to that debris stimulates the pathogens to activate.  Colletotrichum graminicola, the fungus causing anthracnose, is one of those that infects the first few leaves on young corn plant.  This will cause small lesions in leaves and may even spread to upper leaves in a few varieties.  It rarely causes significant yield damage in most varieties and appears to have no relationship to the occurrence of anthracnose stalk rot.  Mostly saprophytic fungi like Fusarium species produce spores on the wet debris to at least feed on any dead or weakened corn plant material in the new plants.  Senescing initial seedling leaves almost always are invaded by Fusarium.  
 
Corn plants at the V6-to V10 growth stage have a leaf whorl that is constantly moist from transpiration in the new leaves.  This makes a nice inoculation chamber for spores of many pathogens to germinate and invade the new leaf tissue.  The moisture in corn whorl may be enhanced with rain but probably moisture from transpiration is adequate for most spores to germinate.  The first line of defense against the invading pathogen occurs in that new leaf tissue.  The first sign of infection that had occurred in the whorl is often a band of small yellow spots on leaves a few days after emerging from the whorl. These chlorotic spots are the result of the plant’s defense system reacting to the invaders at it attempts to stop further spread.  Effective resistance limits the number of lesions developing from this initial infection.  Pathogen success allows further spread within the field.
 
The pre-flowering rain is good, expanding root and leaf growth but does come with the disadvantage of also promoting spread of potential pathogens.