Dear Jorge, Gender allocation is a theory that ratio of male and female expression is influenced by the resources able. When able resources are available females will be favored over males and when less are available males will be favored over females. 

Hormone influence gender expression. Male expression is found with Gibberellic Acid dominance and auixins and ethylene appear to favor female expression. 

Silver is a Gibberellic acid inhibitor I do not think this would necessarily do your job.

In work will papaya I found that the rich nutrient environment was favorable for producing greater females and scarce resource did produce predominantly male. 

Doing a literature review on the particular species you are interested and then screening candidate materials experimentally would be the prudent way of getting good results. 

Good Luck.