TREES, PLEASE! Urban Tree Observations: Conks, Stains, Saps And Bugs
- k-england
- Dec 1
- 4 min read
By Robin Y. Rivet, for Let’s Talk Plants! December 2025.
Urban Tree Observations: Conks, Stains, Saps and Bugs
In October, I wrote about abiotic tree mishaps – especially those inflicted on urban trees by well-meaning humans. Many were preventable, so please re-read that essay if you’re a DIYer, as many of those failures may generate secondary troubles. As we enter our rainy season, (ideally wetter – after years of drought), nature’s wiles may spawn much scarier disruptions to challenge residential trees.
Have you noticed conks, stains, excess sap or weird bugs crawling around a tree? Is it all bad - and what if anything can you do?
Question #1: What is a conk and should you remove it?
Conks are wood-decaying fungal disks typically appearing on tree trunks or emanating around root zones. They are seldom good news. Typical conks are bracket fungi like “turkey tails” -Trametes versicolor or Laetiporus sulphureus - a sulphur shelf fungus; also called “chicken-of-the-woods” because it’s edible when young.
Most conks thrive on dead wood, although a few may parasitize living tissue. Either type are ominous signs of decline. One called “Artist’s Conk” may have vivid coloration and is shaped like an artist’s palette. Beware, fungi are truly a vast subject, so don’t count on a short essay to learn much.
Many trees depend on beneficial mycorrhizal mycelium in soil to communicate their need for additional nutrients, water or light. Whereas underneath tree bark, mycelial plaques may indicate Armillaria – a nasty pathogen of oaks and other regional species. If you note conks or mushrooms, don’t just remove them and hope you’ve cured your tree. You did not. Call a qualified consulting arborist or horticulturist because these fungi indicate decay has been around awhile and tree limbs could fail. Cures are scarce, but mulching with coarse wood chips may help.
Question #2: Is bark staining worrisome?
In one word, yes. Most staining indicates there’s a wound, canker or pathogen that is spreading, even if bacteria is otherwise hidden. Bacterial wetwood (Slime flux) is found in many species and often causes staining. Although it’s smelly, it doesn’t usually kill most trees. A blackened area on or under bark often means there’s an infection like sooty canker near wounds or interior rots. Cankers have many causes. Mulberry trees frequently exhibit blackened crotches, often the result of poor pruning strategies. Like with fungi, there are no magic cures, but otherwise healthy trees can survive.
Question #3: Why is sap oozing out of my tree?
Bleeding sap may be correlated to serious gummosis or just minor wounds, but sap production can also be seasonal and benign as with Sugar Maple collection. Sudden Oak death results in a deadly sap, while eucalyptus may exude sap (sometimes called kino) that may help suffocate boring insects. Conifers often have oozing resins with antiseptic qualities. It’s key to identify your tree and the type of exudate. Sap, mucilage, latex and resin may all drip – but they’re quite different.
Question #4: Insect damage?
Many native insect pests are best left alone, so try to accept some damage - allowing ecological homeostasis to work. Invasive insects are more difficult to predict, isolate or control. We all must help manage those invaders.
· Huanglongbing (HLB) is a citrus greening disease spread by the non-native Asian citrus psyllid (ACP). CA is the last place on earth still staving off the devastating effects of HLB. It’s truly deadly and it’s becoming extremely unlikely we can prevent it from affecting our home citrus. Every sick tree matters.
· The Emerald Ash Borer (EAB) has already destroyed tens of millions of ash trees in the Midwest US and could very likely show up here to annihilate our region’s ashes.
· The Spotted Lantern Fly (SLF) host species are wide and deep, and although it has not yet been found in SoCal, its potential presence could ruin many ornamental and edible urban trees in SoCal.
BIG CAVEAT: Diagnosing and treating tree ailments may involve expensive DNA testing to confirm pathogens, and the skills to distinguish minor damage from deadly disease often requires years of academic education and extensive field experience. There’s excellent University of CA research available for DIYs, but avoid tree salesman selling quick fixes. Most sell nothing but snake oil.
