Gardening & Landscaping Stack Exchange is a question and answer site for gardeners and landscapers. It only takes a minute to sign up.
Sign up to join this community
Unfortunately this lemon tree hasn't grown for the last 3 years when it was planted. Its situated on the north side of the house and should have plenty of sun although it's winter now in Melbourne. There are these strange lumps on the stalks which could be affecting its health. Any help would be greatly appreciated!
By now you already know that what you have is a citrus gall wasp infestation. According to the link above (the agric.wa.gov.au one) all the galls (but the old/empty ones) should be cut and destroyed in June or July. All the literature out there seems to indicate that once these nasty little creatures lay their eggs inside the branches there's no spray or poison that would permeate sufficiently deep (into the branches) to kill them off. Thus all the treatment out there aims for soil disinfection and warding the wasps off.
So what you can do now (until June) is to monitor for galls, apply soil-based insecticides (and advise your neighbors to do the same, otherwise all your effort might go in vain) and perhaps apply some foliar spray to encourage leaf and branch growth (or apply some fertilizer nowish, but not after winter, because that would just make the infestation even worse, foliar spray on the other hand is more of a "cosmetic" measure instead).
