Three days ago I snapped the suckers off 6 Virginia Brightleaf (VBL)and applied about 3 drops of mineral oil to where the suckers were. I then suckered the remaining 40 VBL but did not apply any mineral oil. I just checked today and the 6 treated VBL's have no sucker growth. The untreated VBL already had gigantic suckers and it's only been 3 days. Might seem time consuming but I think if you sucker once and apply mineral oil you'll probably be done for the rest of the year.