I Have Seen This Pattern Before

I have seen this pattern before.

During my time at the University of Minnesota, I saw firsthand what emerald ash borer meant for mature ash trees. The early years still left room for people to treat the insect as a distant problem. Then the losses became ordinary. Trees that had taken decades to grow were suddenly on treatment schedules, removal lists, or already gone.

South American palm weevil is not emerald ash borer. They are different insects, attacking different trees in different landscapes. I am not claiming that their biology or eventual impact will be identical. I am saying that the pattern feels uncomfortably familiar: an invasive borer becomes established, early damage is difficult to see, public response trails the insect, and mature trees begin disappearing faster than they can be replaced.

The useful lesson from Minnesota

The lesson is not that every tree must receive the same treatment. The lesson is that owners of valuable, susceptible trees need to decide before obvious decline makes the decision for them.

The University of Minnesota now states the problem plainly: emerald ash borer has killed hundreds of millions of ash trees in North America, untreated ash trees are killed, and healthy high-value trees can be protected with recurring insecticide treatment. USDA APHIS also emphasizes why the insect gained so much ground: early infestations are difficult to detect because much of the damage is hidden while decline develops gradually.

That is the part San Diego palm owners should recognize. Waiting for a Canary Island date palm to look severely damaged is not a conservative decision. It is a decision to give up the period when protection is most practical.

Visible decline is late information

South American palm weevil larvae feed inside the crown. By the time the newest growth collapses, the crown thins, or the canopy takes on the unmistakable look of failure, substantial internal damage may already exist. A photograph can show the change. It cannot recover the time that was lost before the change became obvious.

UC Agriculture and Natural Resources reports that SAPW is established in San Diego County, is killing Canary Island date palms, and has been detected northward into San Marcos. Its management guidance calls for monitoring, early action, and preventive protection of susceptible palms with systemic insecticide. It also notes that several treatments per year may be needed, depending on the treatment program and label.

My position is direct: if you own a healthy, mature Canary Island date palm in an affected area and want to keep it, preventive treatment deserves serious consideration now. Treatment must be appropriate for the palm and site, performed under the pesticide label, and supported by continuing observation. It is not a guarantee. It is a practical attempt to protect something that cannot be replaced on demand.

This is not a scare post

Fear is not useful. Neither is pretending that the problem will remain somewhere else.

Mature palms add real value to estates, commercial properties, neighborhoods, and public landscapes. A large Canary Island date palm can define a property for generations. Once it is lost, buying another palm does not buy back its age, scale, or history.

Owners still have choices: establish the palm's present condition, monitor it, reduce avoidable stress, use preventive treatment where appropriate, and respond quickly to meaningful change. Those choices become narrower after the crown begins to fail.

I watched communities in Minnesota learn that lesson with ash trees. My personal opinion is that San Diego will learn it with mature date palms unless we recognize the pattern sooner.

Things will get worse before they get better. The question is how many mature specimens will still be standing when the broader response finally catches up.

Sources and further reading

• University of Minnesota Extension — Emerald ash borer in Minnesota
• USDA APHIS — Emerald Ash Borer
• UC Statewide IPM Program — Giant Palm Weevils
• UC Agriculture and Natural Resources — SAPW Management Options
• UC Agriculture and Natural Resources — SAPW Frequently Asked Questions