residuals in lmer

Does anyone know how to extract residuals in lmer?

Here's the error I get:
 >  
crop.lme=lmer(response~variety*irrigation*pesticide+(1|rep)+(1|rep: 
pesticide)+(1|rep:pesticide:irrigation), crop.data)
 > qqnorm(crop.lme)
Error in qqnorm.default(crop.lme) : y is empty or has only NAs
 > resid(crop.lme)
NULL

Thanks!

--Jake