Cultural techniques for managing disease are not recommended unless they have been scientifically tested to show both efficacy and a lack of adverse effects. Many SOD-infected oaks and tanoaks have symptoms that fail to progress for multiple years or may go into complete remission (see 1.4.1.4. Changes in Canker Appearance over Time). Consequently, anecdotal or case-study reports can not be relied on as demonstration of efficacy of SOD treatments: symptom remission can be unrelated to applied treatments. To document a real effect, treatments need to be tested under experimental protocols that include an adequate number of appropriately matched nontreated controls. Due to the slow progress of SOD in many trees, and years during which few or no new infections occur, studies typically need to last at least five years to produce meaningful results.
Cultural techniques for managing disease are not recommended unless they have been scientifically tested to show both efficacy and a lack of adverse effects. Many oaks and tanoaks infected by P. ramorum have symptoms that fail to progress for multiple years or may go into complete remission (see "Patterns of canker development" in section 1.4.1). Because symptom remission can occur with or without treatment, anecdotal or case-study reports of treated trees do not provide proof that SOD treatments are effective. To document a real effect, treatments need to be tested under experimental protocols that include an adequate number of appropriately matched untreated controls. Because of the slow progress of SOD in many trees, and years during which few or no new infections occur, studies typically need to last at least 5 years to produce meaningful results.
Arborists recommend various cultural practices to enhance or maintain oak tree vigor as a general prescription to maintain tree health or counteract decline. These practices may include:
Root zone mulching.
Fertilization.
Light irrigation in the outer portion of the root zone.
Radial trenching or other manipulations to reduce soil compaction.
Application of mycorrhizal inoculants or other soil amendments.
Light pruning.
Removal of competing vegetation under the canopy.
If appropriately applied, some of these practices have the potential to stimulate new shoot growth and improve tree appearance, at least over the short term. However, there is no evidence that any of these practices provide any protection against SOD or enhance survival in infected trees.
Furthermore, high tree vigor is associated with an increased risk of developing SOD in coast live oak (see "Effects of tree size and condition" in section 1.3.2., and table 2-5). Because measures intended to increase tree vigor have the potential to increase disease risk, they are not recommended for managing trees at risk of developing SOD.
One marketed tree vigor prescription involves the use of a liming material (Azomite® Soil Sweetener—40 to 50 percent limestone [calcium carbonate]) applied to the soil around affected trees to raise soil pH. The method also calls for coating the lower portion of the trunk with a lime suspension (Arboright® limewash—26.8 percent calcium hydroxide), a material "intended for topical use to prevent sunburn," according to its label. No epidemiological or biological data suggests that there is any relationship between soil pH and P. ramorum canker. Furthermore, in controlled studies with both potted and field grown coast live oaks, this treatment provided no measurable protection against P. ramorum, whereas phosphite significantly reduced disease susceptibility (Garbelotto and Schmidt 2009).