These two disease pathogens thrive in a warm and moist environment. This condition is created when an irrigation system is used beneath coast live oak and other plants adapted to Mediterranean climate during summer months.
Coastal California is considered a Mediterranean climate. Plants adapted to this climate require winter water and summer drought. Watering during summer makes them susceptible to disease.
There is an exception to the no irrigation in summer. During drought periods a monthly application of water is recommended. Apply enough water to soak downward 4-8 inches into the feeder root system. This is where the roots that are responsible for bringing resources to a plant are located.
Crown rot-Root rot
Landscaping and planting anything, especially lawns, beneath the canopy of oak trees should be minimized or avoided altogether. (Oak tree in lawn picture) Installation and use of irrigation systems is one of the leading causes of oak decline and mortality as roots are severed during pipe trenching process. Lawns require large amounts of water during summer months. This creates the perfect condition to trigger pathogen activity. A decision has to be made between having a healthy native tree, or a lawn.
Landscaping Beneath Oak Trees
Incorrect placement of irrigation emitters is a leading cause of root and crown rot disease. It is common practice in the landscape industry to place irrigation emitters next to tree and shrub stems. This will eventually lead to crown rot.
Although it may not be a problem initially, it is bad practice to leave them there after the initial root establishment period (1-2 years). Roots should be encouraged to grow outward in search of moisture and nutrients. A second often used technique is to direct irrigation spray onto tree trunks. This must be avoided at all costs. Both techniques often lead to disease and catastrophic stem failure.