How do I merge 2 similar data frames but have one with greater importance?

For example:

Dataframe 1

Date      Col1    Col2
jan         2      1
feb         4      2
march       6      3
april       8      NA

Dataframe 2

Date      Col2    Col3
jan         9      10
feb         8      20
march       7      30
april       6      40

merge these by Date with dataframe 1 taking precedence but dataframe 2 filling blanks

DataframeMerge

Date      Col1    Col2    Col3
jan         2       1      10
feb         4       2      20
march       6       3      30
april       8       6      40

EDIT - SOLUTION

commonNames <- names(df1)[which(colnames(df1) %in% colnames(df2))]
commonNames <- commonNames[commonNames != "key"]
dfmerge<- merge(df1,df2,by="key",all=T)
for(i in commonNames){
  left <- paste(i, ".x", sep="")
  right <- paste(i, ".y", sep="")
  dfmerge[is.na(dfmerge[left]),left] <- dfmerge[is.na(dfmerge[left]),right]
  dfmerge[right]<- NULL
  colnames(dfmerge)[colnames(dfmerge) == left] <- i
}
r merge
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