TREES, PLEASE! Is That Tree Really Sick?
- k-england
- Sep 30
- 3 min read
By Robin Y. Rivet, for Let's Talk Plants! October 2025.
Is That Tree Really Sick?
“I think my tree is dying”.
Sadly, this is a common lament for far too many residents. Decline of urban trees often arises from largely preventable abiotic causes. Environmentally stressed trees then become susceptible to more serious pests and diseases, so here’s some preemptive questions to ask yourself if you sense trouble - with tips for DIY self-help.
Question#1: Is it possible your tree is just going dormant?
· Several native CA species may go summer dormant during very hot dry weather.
· If tree foliage stays green all winter, but by spring it starts looking bedraggled, first rule out irregular phenological dormancy. San Diego’s famed Jacaranda sports a full canopy at Christmas, but appears naked during May gray. Although many people recognize this, it’s amazing how often Mediterranean species native to the southern hemisphere will drop leaves during springtime here, since their DNA thinks that it’s really fall.
· Evergreen sub-tropical fruit trees like avocado or sapote may de-foliate briefly in spring, dropping last year’s leaves hastily - just as they’re making new ones; falsely alarming their owners.
· Ficus have been known to drop their foliage – simply from being moved across a room where the light changes.
Question #2: How was it purchased and planted?
· Confirm the type of tree you have? Verify its genus, species, cultivar and rootstock - if grafted.
· Was it a large, boxed-specimen? These are very difficult to procure free from girdling roots and their size makes it hard to check and modify those roots for long term success.
· A tree planted too deeply may be susceptible to limited gas exchange and an inability to survive over time.
· If a tree’s roots were not spread apart at planting, those tangled roots may swell and constrict free flow of oxygen and water over time; showing up 5-10 years later.
· If soil amendments or gravel were added to the hole at planting time, this encourages both girdled roots and a perched water table, effectively keeping those roots balled up to rest in a puddle of anaerobic muck at the base of your original planting hole. Rot often ensues.
Proper planting guidelines: https://ucanr.edu/sites/default/files/2011-03/80160.pdf
Question #3: How is it watered or pruned?
· Feeder roots exist at the perimeter of the canopy, so water needs to be applied there, and penetrate down a foot or more. This typically mean many hours with typical drip system applications. Shallow watering generally doesn’t do trees any good, and be sure keep water away from the trunk.
· Pruning a sick tree typically causes wounds that further may stress it. It’s better to wait to prune unless you know for certain a limb is dead or a disease is spreading – as defoliated branches may recover.
Question #4: Have you applied chemical treatments nearby?
· Herbicides used to kill adjacent weeds can be absorbed by bark, foliage or roots.
· Never apply broad-spectrum insecticides without knowing EXACTLY what pest you are combatting.
· Over-the-counter “natural” products should also only be used with knowledge and care. If you do not know what is causing a problem, do not spray anything until you are certain of what you are trying to eradicate. Fungicides won’t cure bacterial issues. Insecticides won’t cure viruses. Smothering oils that make breathing difficult for insects - can also make it hard for plants to breathe.
· The only “chemical” that can alleviates drought - is water.
Stay tuned for what to do if you observe conks, sap, stains, or insects.
