My tree is contaminated with scale and I am in the midst of cutting all the leaves/branches. The tree trunk appear to be infected minimally. Can I use Insect pest killer with 20 g/l petroleum oil, 0.3 g/l pyrethrins, 1.2 g/l poiperonyl butoxide to spray the denude tree trunk and branches? Thanks

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  • Read and follow the advice given in the question/answer linked to in the other comment above, the treatment you are proposing is too aggressive - if you use the leaves from your tree in cooking, make sure any treatment you use on the tree for the scale is not likely to poison a human being if a leaf or three is added to whatever dish you are producing. – Bamboo Mar 18 '18 at 12:06

In our area (southern hemisphere, subtropical climate) Bay trees tend to send out new growth once a year.

The old leaves particularly tend to become susceptible to scale towards the end of this annual cycle and in the one or two months leading up to the new flush of growth.

The new growth, when it emerges, will be very tender and although will not have any scale initially, the scale will eventually spread.

However the new growth, tender for the first few weeks, will be less capable of coping with a coating of petroleum oil and may brown off.

I’d recommend spraying a petroleum oil only spray, mixed with a small squirt of dishwashing liquid as surfactant, before the new growth emerges.

The petroleum oil is all that is needed, as it suffocates the scale insect by coating it in an oily film that excludes oxygen. The other chemicals are in my opinion unnecessary and may harm other beneficial transient insects that use the tree intermittently.

In my experience, it will be ok to apply the petroleum oil sprayed onto your cut back tree.

Also in my experience, I’d recommend applying a liquid tonic (seaweed extract or worm casting tea) every two weeks, to help strengthen the health of the tree. Applying compost and mulch to the top of the soil around the base of the tree would also greatly improve the health of the tree and help the tree fight off potential future infestations.

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