Silk as infection site

​Nutrition and moisture in corn silks allow the fast movement of the pollen tube towards the ovule and contribution of the male genetics to the next generation.  Those same favorable silk characteristics also can be used by invading fungi. Rapid deterioration of the silk tissue after pollen tube growth offers protection within a few days after pollination, but environments and genetics can have a drastic effect on the time of silk vulnerability and the biology of potential invaders. Aspergillus flavusgets much attention because of is dangerous toxin produced on infected corn.  Fusarium verticilloidesis another common invader of corn kernels through silk infection that can produce a mycotoxin (i.e. fumonisin). Others such as Diplodia maydisand Gibberella zeaealso can utilize the silks and initial entry into the ear.
 
These fungi are mostly saprophytic feeders on plant debris and intensity of their spore production is greatly dependent of corn debris from the previous season near the new crop plants. Their biology also is influenced by the environment affecting competition with other saprophytes feeding on debris and production of spores when the silks are exposed.
 
Duration of silk vulnerability is also associated with environment.  Cool, moist weather a few weeks before normal pollination may cause silks to be exposed before pollen is produced- and may favor Diplodia(Stenocarpella) maydis.  Extended dry, warm periods during the pre-pollination time, may cause pollen production before silk elongation and exposure but favor Aspergillus flavussporulation and distribution by the time the un-pollinated silks do emerge.  Fusarium species (including Gibberella zeae) produce massive numbers of spores under most environments. 
 
Plant pathologist have shown that one can induce ear infection by directly spraying the silks with the spores of each of these pathogens.  These studies have shown evidence of resistance variance among genotypes but usually only on a scale and not of absolute absence of disease.  Evaluation for resistance from natural infection is not easy.  One can record occurrence of infection within plots, but each genotype may not be exposed to the same environments, including time of silk exposure.  One does need to use care before drawing conclusions about ear rot susceptibility based upon single location observations.
 
Ear rots are prime examples of the complex biology of host and pathogens interacting with environments.  Ear rot may not be noticed until harvest, but the problem involved the dynamics occurring at pollination time of the season.