A group of lemon-loving locals have stepped up their fight against the native gall wasp, launching a campaign asking Melburnians to Prune in June.
The tiny wasp, which is native to northern New South Wales and Queensland, lays its eggs in the branches of citrus trees, causing bulging lumps called gall.
Save Our Citrus Melbourne was formed last year by two gardeners concerned about the spread of gall in Melbourne's lemon trees.
Co-founder Kaye Roberts-Palmer said they were initially focused on their local council area of Darebin, but soon expanded their sights to the whole of Melbourne.
"We did a few talks and we were amazed by the interest — it's just grown and grown," she said.
Lemon trees 'important to Melbourne culture'
The group has launched a Prune in June campaign, which includes online videos aimed at teaching people how and when to prune their citrus trees.
Ms Roberts-Palmer said that along with olive trees, lemon trees were "Melbourne icons".
"I think they're really important to Melbourne culture; along with the footy, along with the coffee, I think they're something that should survive and thrive," she said.
Ms Roberts-Palmer said a lemon tree she saw at a friend's rental property was an example of what could happen when gall-infected branches were not pruned.
"It looks like the tree has cancer ... it is very depressing," she said.
"The good news is that citrus trees are a very hardy species."
Older trees with extensive root systems can be cut right back and still survive, she said.
Pruning in June stops gall spreading.
Ms Roberts-Palmer said it was important to prune citrus trees while the weather was still cold.
"We really want everyone to get out in June and prune their citrus trees," she said.
"In the winter months the citrus gall wasp is still dormant, and so what we can do as gardeners is get out there and cut off the galls."
She said the gall wasps would spread if owners waited until spring to prune.
"The wasps start hatching and flying around," she said.
Pruned galls should be soaked in water for two weeks, then bagged and thrown in the rubbish.
Videos, workshops teach citrus owners how to prune.
Ms Roberts-Palmer said learning how to prune citrus correctly was crucial to maintaining a healthy tree.
"When you're cutting into the tree, you're actually wounding the tree," she said.
The group's instructional videos show viewers what a gall looks like and how to prune it off the tree.
Along with the videos, Save Our Citrus is conducting a series of how-to prune workshops throughout June.
Ms Roberts-Palmer said controlling the spread of gall in Melbourne would take several years of concerted effort.
"There's no natural predator in Victoria that's going to affect this gall wasp," she said.
"It's really about us all getting together and pruning."
A list of workshops times and venues is available on the Save Our Citrus Melbourne Facebook page.