Become A Tree Pest Detective!
The Polyphagous/Kuroshio Shot Hole Borer/Fusarium Dieback (PSHB/FD) is a non-native ambrosia beetle/fungi complex that has invaded southern California and is currently threatening tens of thousands of native, residential, and agricultural trees, and is challenging our ability to sustain natural ecosystems and food systems. Our goals is to understand where the pest is currently found and to estimate its rate of spread early enough to respond effectively. To do this, we need your help!
Why are oak trees protected by law?
What is my oak worth?
Another way to think about the value of an oak is based on the benefits it provides. A study done by American Forests in 1985 found that each mature tree provided $275 worth of real economic benefits each year. These benefits are avoided costs for stormwater runoff control, groundwater infiltration, temperature moderation, air pollution reduction, and carbon sequestration. A mature tree located on the west side of a house significantly reduces summer air conditioning costs.
Finally, in the Santa Monica Mountains, homes having mature oaks typically sell for up to 30% more than homes without them.
What causes the brown patches of dead twigs in oak trees?
Are there Oak Pests and Diseases I should watch for?
How come there are lots of acorns some years, and few others?
Why should I not irrigate under my oak tree?
What can I plant under oak trees?
A good strategy for obtaining seasonal color under the trees is to use pots that are watered either by drip or by hand. These pots can hold all the thirsty colorful plants like azaleas, begonias, impatiens, camellias, etc. that are a problem for the tree when planted directly in the soil.
Why should I prune?
- To reduce fuel available to fire
- To limit size of the plant (Best to plant the right tree in the right spot so that this is minimal)
- To enhance plant health
- To enhance plant structure (Remove crowded, crossed branches, weak branch crotch angles, establish main leader)
- To remove suckers or water sprouts (But why are they present? Possibly due to previous poor pruning or disease. Check first for problems)
- To improve or maintain flowering and fruiting
- For safety-branches overhanging walkways, obstruct vision, low hanging
- To retrain tree that has been poorly pruned previously
When is the best time to prune my oak tree?
What should I prune?
- Branches that cross each other
- Broken or damaged branches
- Branches rubbing against other trees or structures (The Fire Dept. requires a 10′ clearance from all structures, especially chimneys!)
- Diseased branches (However, be sure to clean your clippers in solution of 1 gallon water with 3 tablespoons Clorox between cuts so as not to spread disease.)
The rule of thumb for pruning is to remove no more than 15% of the living leaves. Less is definitely more when it comes to pruning. The leaves produce the food for the tree. Removing large portions of the canopy at once is a severe stress on the tree, forcing it to use stored energy reserves to replace the lost foliage. The tree will often sprout twigs from large branches (call sucker sprouts, epicormic growth) in an effort to generate as much leaf surface as possible. If a tree has been severely pruned, then it might be necessary to leave these sprouts to grow for a while until the outer canopy recovers.
How should I prune?
The best pruning job is so subtle that you can’t even tell the tree was cut! Unfortunately, examples of bad pruning are much more common than good examples, and having trees trimmed is expensive. Resist the temptation to get your money’s worth by trimming too much at once! It really pays to do a little at a time.
- For large branches, especially those that cannot be reached from the ground, it is usually best to call a professional
- For smaller, accessible branches, use sharp tools and make cuts at the nodes
In Los Angeles County, a permit is required to prune living limbs larger than 2″ diameter from native California Oak trees. Permits can be obtained from LA CO. Regional Planning (213-974-6411). The LA County Foresters may waive fees in some situations, i.e. if tree presents a hazard. Call them when in doubt to see if you qualify. (818-222-1108)
How do I choose a professional to prune my oaks?
Remember, you get what you pay for! Experienced tree care professionals cost more than a gardener with a chainsaw because they know more!
Be sure to:
- Ask for evidence of contractors license, certificate of insurance and workers compensation (CA law requires that arborists doing tree work worth more than $350.00 have a contractors license and insurance)
- Look for arborist certification and training (International Society of Arboriculture or National Arborist Association membership)
- Clarify in writing what specific work will be done, how cleanup will be dealt with and the fee for services
- Climbing with spikes-this is only done when a tree is to be removed
- Topping-this can kill your tree, it can create a hazard by encouraging weakly attached shoots, and it looks terrible!
- Poorly equipped personnel-safety while climbing trees is critical! Pros have proper saddles and ropes, a person on the ground, and they wear appropriate protective clothing when handling chainsaws or chemicals.