Plant Doctor Archive

 CAN you please tell me what is causing this damage on my trees and roses? It is killing off parts of the branches. I had an idea it was cicadas, but don’t they develop below ground?

  THE damage to the twigs was caused when an adult female cicada laid her eggs in that typical herringbone pattern which causes long scars to develop in the branch. The eggs take many months to hatch, during which time they are kept nice and moist, protected within the branch tissues. When they eventually hatch, the nymphs wriggle free, fall to the ground and work their way down cracks in the soil until they are well below ground where they feed on sap from tree roots. By this time the original damage caused in laying the eggs has weakened twigs and branches to the point where they often break off under their own weight or in wind.

Some of the most serious cicada damage I’ve seen was in an orchard planted close to native bush where branches on the apple and pear trees were so weakened they collapsed under the weight of even a light load of fruit.

Cicada nymphs spend many months in the soil before they reappear above ground and moult into the chirruping insect whose raucous chorus is such a familiar late summer sound in many parts of the country.

Adult cicadas only live for a month or two, during which time they mate, the female lays its eggs and the cycle starts over again.

Overseas, one species of cicada is known to spend up to 17 years underground as a nymph, but New Zealand species have a much shorter life cycle.

Unfortunately, there’s very little you can do to prevent cicada damage apart from pruning out damaged branches when you spot them.

Weekend Gardener, Issue 176, 2005, Page 34

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