writing dates to a file

Hi,

I have attached the data files to this note.   I use this code:

library(zoo)
z1 <- read.zoo("baltimorefludata.txt", format = "%m/%d/%Y", header =  
TRUE)
z2 <- read.zoo("baltimorew.txt", format = "%Y%m%d", header = TRUE)

z3<-merge(z1,z2)

write.table(z3, "fluweatherdata_baltimore2.txt", sep="\t")

R is writing the other data to the file but not the dates...  Is  
there a way to also write the dates to the file?  Thank you!!