Scale Infestation on Laurel bush
Just before I went on vacation a few weeks ago, I noticed some brown leaves and scale (I think) on a laurel bush in the front of my house. I removed the dead branches and I sprayed some Neem Oil on other parts of it, but it has been untreated for three weeks. In the meantime, the scale has increased and I don't think I can treat it with the small bottle I have. Is there a source where I can get this in larger quantity and then spray it with a larger professional sprayer, if in fact, this is the best way to treat it? Would it be better to use something more systemic? These are two 30+ year-old bushes that I hope I can save. If the treatment you recommend doesn't work (how long will it take?), is it okay to replace these with the same type of plant or would they also become infested? Would I have to wait until after freezing weather and then plant in the Spring? Thanks for any help you can give....!
Howard County Maryland
Hi - White prunicola scale is very challenging to manage. When there is a heavy infestation of white prunicola scale and plant dieback is severe, it may be best to remove the shrub altogether rather than try to treat it. In your case, you may be able to prune out branches selectively and discard them to remove as much of the infestation as possible.
Fertilized female scales overwinter on the bark of the branches, so the next step in management is to apply a dormant rate of horticultural oil during the dormant season (when deciduous plants have lost their leaves). You can first use a soft-bristled brush to scrub off the scale patches gently. Then apply the horticultural oil.
If female scales remain on the shrub, juveniles (called “crawlers”) will emerge in the spring. Crawler periods vary from year to year depending on temperatures. For this species, new generations may be out in May, mid-July to mid-August, and September. The tiny juvenile crawlers are salmon-colored. You can place a simple trap to detect their activity; wrap a piece of double-sided tape around a few branches. When you see crawlers stuck to the tape that is the ideal time to apply horticultural oil. That is when the insects are most vulnerable. Horticultural oil spray is recommended, as it is the least harmful to beneficial insects in your landscape.
If you replace this shrub with the same type of plant, yes, there is a chance it will get the same problem. Plants in the Prunus genus, which includes cherry laurel, are a preferred host plant for this insect.
This article provides more information about cherry laurels and how to give them the right growing conditions to keep them healthy. https://marylandgrows.umd.edu/2019/01/07/qa-whats-wrong-with-my-cherry-laurel-shrubs/