How can I get Tukeys letters and/or an LSD for a split plot design?

I have a split plot design with the 6 varieties nested into 5 rates along with 4 replications and would like to see the Tukey's test letters or a number for the least significant difference between the values.

Here is my data:

dput((dataChippers))
structure(list(Plot = c(1011L, 1012L, 1014L, 1024L, 1025L, 1026L, 
1031L, 1033L, 1036L, 1041L, 1042L, 1045L, 1052L, 1053L, 1055L, 
1061L, 1062L, 1066L, 1071L, 1073L, 1076L, 1083L, 1084L, 1085L, 
1092L, 1094L, 1096L, 1102L, 1103L, 1105L, 1111L, 1112L, 1116L, 
1121L, 1122L, 1123L, 1132L, 1133L, 1135L, 1141L, 1142L, 1144L, 
1151L, 1153L, 1155L, 1161L, 1162L, 1164L, 1171L, 1172L, 1175L, 
1183L, 1185L, 1186L, 1192L, 1193L, 1196L, 1202L, 1204L, 1205L
), Variety = structure(c(3L, 2L, 6L, 6L, 3L, 2L, 3L, 2L, 6L, 
6L, 2L, 3L, 3L, 2L, 6L, 2L, 6L, 3L, 3L, 6L, 2L, 6L, 2L, 3L, 3L, 
6L, 2L, 6L, 3L, 2L, 2L, 6L, 3L, 6L, 2L, 3L, 2L, 3L, 6L, 2L, 6L, 
3L, 3L, 2L, 6L, 6L, 2L, 3L, 3L, 6L, 2L, 3L, 2L, 6L, 3L, 6L, 2L, 
3L, 6L, 2L), .Label = c("Burbank", "Hodag", "Lamoka", "Norkotah", 
"Silverton", "Snowden"), class = "factor"), Rate = c(3L, 3L, 
3L, 5L, 5L, 5L, 3L, 3L, 3L, 5L, 5L, 5L, 5L, 5L, 5L, 1L, 1L, 1L, 
3L, 3L, 3L, 2L, 2L, 2L, 4L, 4L, 4L, 2L, 2L, 2L, 4L, 4L, 4L, 4L, 
4L, 4L, 2L, 2L, 2L, 4L, 4L, 4L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 
2L, 1L, 1L, 1L, 5L, 5L, 5L, 3L, 3L, 3L), Rep = c(1L, 1L, 1L, 
3L, 3L, 3L, 2L, 2L, 2L, 1L, 1L, 1L, 4L, 4L, 4L, 2L, 2L, 2L, 4L, 
4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 3L, 3L, 3L, 1L, 1L, 1L, 2L, 2L, 
2L, 2L, 2L, 2L, 3L, 3L, 3L, 4L, 4L, 4L, 3L, 3L, 3L, 1L, 1L, 1L, 
1L, 1L, 1L, 2L, 2L, 2L, 3L, 3L, 3L), SG = c(1.076, 1.076, 1.07, 
1.075, 1.073, 1.075, 1.078, 1.078, 1.075, 1.074, 1.08, 1.072, 
1.075, 1.075, 1.075, 1.076, 1.078, 1.074, 1.07, 1.076, 1.077, 
1.073, 1.076, 1.074, 1.075, 1.073, 1.075, 1.073, 1.072, 1.073, 
1.075, 1.076, 1.081, 1.076, 1.08, 1.071, 1.079, 1.071, 1.075, 
1.074, 1.079, 1.077, 1.073, 1.07, 1.075, 1.079, 1.078, 1.071, 
1.074, 1.075, 1.082, 1.073, 1.066, 1.074, 1.059, 1.078, 1.078, 
1.073, 1.074, 1.078), HH = c(0L, 1L, 0L, 0L, 0L, 3L, 0L, 1L, 
0L, 0L, 2L, 0L, 0L, 2L, 0L, 1L, 1L, 0L, 0L, 1L, 0L, 0L, 2L, 0L, 
1L, 0L, 3L, 0L, 0L, 3L, 0L, 0L, 0L, 0L, 2L, 0L, 2L, 0L, 0L, 2L, 
0L, 0L, 0L, 2L, 1L, 0L, 3L, 0L, 0L, 1L, 3L, 4L, 1L, 1L, 0L, 0L, 
0L, 0L, 0L, 2L), row.names = c(NA, -60L), class = "data.frame")

And here is my attempt at making a model for the response variable SG:

require(agricolae)
model <- with(dataChippers, sp.plot(Rep, Rate, Variety, SG))

Unfortunately, I'm not sure where to go from here. Thanks for any help, and feel free to let me know if I have formatting anything incorrectly