Scale insects on lemon tree.

 

A customer bought in a lemon the other day and it was amazing how many scales were on just this one lemon, let alone what must have been on the branches.

These scales eat the goodness out of the plant cells. They can literally bite into the skin of the plant.

Heavy infestations like this one will weigh heavily on the plant. Often a weaker plant will then be left vulnerable to a getting a secondary problem. One such secondary problem is sooty mould which will grow on the sugary waste from the scales called honeydew. Ants may also may inhabit the plant in greater numbers and even assist scales by carrying around young insects and clearing away all the honeydew that might otherwise choke a scale colony.

The plant branches and leaves may then have poor distorted growth and eventually branches could even die. Fruit like this can be contaminated or dis-coloured, although this particular fruit still appeared to be ok inside.

Scales are weird because they don't really look like insects at all. For most of their life cycle they are hiding under protective shells. They overwinter as mature females, and lose the use of their legs.

In spring, the females produce 'crawlers' which are very young insects which move out from under the shells and move to new feeding sites. They then form the shell like scale and can no longer move. Many generations can be produced over one summer. They infect fruit like this late in the season. Only the small males fly, but 'crawlers' can be blown in the wind.

Control: This plant should have been sprayed with white oil (also sold as Pest oil) in the warmer months, being careful not to burn the plant. Do it on a cloudy day, and maybe even with a test spray. It could still be white oiled in winter, but the insects are much more protected by then and it will be less effective. You could also prune the tree now and dispose of the branches in the bin. An insecticide like Carbaryl could also be used, but stay on top of this problem with white oil, and instead wait for the ladybirds to help you in summer.

Comments

[Ted Gannaway]

My myer lemons are covered in a brown scale, some of them 100% and others a little less. I have sprayed them with pest oil. Will the scale disappear? How often should I spray them. My neighbour has no sign of scale on his.

Cheers
Ted
21 Hymes Street
CAIRNS 4870

[Dennis Ting]

The scale insects will be smothered by the pest oil and die off. They tend to dry up and drop from the tree or can be rubbed/washed off by spraying the tree with water from a hose etc. Sometimes two to three treatments may be required to kill all the scale and baby crawlers and these sprays can be up to a month apart.