To generate a line graph with y error bars you can use the Chart-platform under the Graph-menu. Select the line chart from the options in the lower left corner. As X select your treatments, and as Y select your data with the "Mean" option (if you also want individual points in your graph select your Y's twice: as "Data "and as "Mean").
Then in the resulting graph under the red triangle there is the option to add error bars for the mean. You will be prompted to choose from standard error, standard deviation, confidence limits etc.