It is a common gardening myth that rubbing vaseline (petroleum jelly) around the trunks of citrus trees will reduce citrus scale and aphids by deterring ants from climbing up the trees and feeding the aphids and scale.
Gardening Australia even has a fact sheet* recommending this approach.
Sometimes the vaseline method is recommended for other insect pests. In her otherwise excellent book One Magic Square, Lolo Houbein recommends treating apple, fig, pear and quince trees with petroleum jelly to deter codlin moth caterpillars from climbing up the trunks:
Commercial products such as a horticultural glue fixed around the trunk to prevent caterpillars climbing up may help, or use petroleum jelly. (my italics)
I beg you, please DO NOT rub vaseline on the bark of your fruit trees. Not only will the vaseline NOT deter ants and other pests, but it may eat away the bark, ring-barking and possibly killing the tree.
I know this from experience. On the advice of a gardening forum, in spring 2012 I rubbed vaseline around the trunks of my young mandarin and lime trees. Later the same day I read that this wasn’t a good idea so I washed the vaseline off. The vaseline only remained on the trees for a few hours.
Within days the outer bark of both trees was disintegrating. Sadly, the mandarin tree died but the lime tree survived because the damage was not all the way around the trunk.
While the lime tree is now thriving, the damage to the bark is still evident. I took the photo below this morning and you can see the pale and gnarled patches where the vaseline damage occurred. The normal bark is visible above and below the damage.
(For organic ways to treat aphids and other insect pests, read my post on how to get rid of aphids organically.)
Have you ever followed advice to treat fruit trees with petroleum jelly? What was the outcome?
*I have emailed Gardening Australia asking them to remove this fact sheet from their website.