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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!

  • This little tree needs chemistry. Have you applied any fertilizer? If so, what and how much? Make sure that soil level is not above the bark of the trunk; just the roots need to be under the soil. A plant that is healthy is able to protect itself from disease and insects. Is this tree in the shade of the home on the north side? And remove that green plastic strip. Is that embedded in the trunk? – stormy Jun 9 '18 at 9:18
  • Hi stormy, I think we used vegetable fertiliser and blood and bone fertiliser when we planted it . We haven't added fertiliser in a long time but it was topped up below the bark. It doesn't have much shade on the north side except for the afternoons. – Alex Liao Jun 10 '18 at 4:05
  • Also what is your opinion on the best way to pendent gall wasps – Alex Liao Jun 10 '18 at 4:15
  • First thing is a healthy vigorous plant. Plants are able to fight of disease and insects when they are healthy. Could you send a close up, please? Looking at this plant against the fence, I would cut at an angle just above that bud pointing to the left; second horizontal on fence bottom edge? Osmocote 14-14-14 or a tree fertilizer stake. I'll go check on this a bit more for you, okay? – stormy Jun 10 '18 at 21:33
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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).

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