Sex Gives Farmers Troubles

That's my takeaway from a Stu Ellis piece on waterhemp, a weed which is very difficult for farmers to control.  The reason, although I'm reading between the lines and making assumptions, is sex:

Since the waterhemp family has both male and female plants whose genes mix annually, the genetic diversity increases every year and an increasing number of plants have become resistant to a wider variety of herbicides. 

 If I recall my biology, that's the purpose of having sex, to increase diversity and therefore increase adaptability to the environment.  I'm glad to know some of my knowledge isn't obsolete.