Understanding and Managing Sudden Oak Death in California

2.2. Management Strategies for Different Stages of the SOD Epidemic

Stand conditions change after P. ramorum invades. Over time, SOD affects progressively higher percentages of the canker hosts in the stand. As a result, SOD management objectives change with the SOD disease stage (table 2-2). As shown in table 2-2, the SOD disease stage of a given stand can be considered under the broad categories of Before, During, and After. Specific considerations for managing SOD at these epidemic stages are discussed briefly in the respective sections below.

The severity of SOD impacts often varies over short distances. It may be useful to divide management units into areas in which the predominant SOD disease stage is relatively uniform. Management in these different areas needs to reflect the current disease impact stage and may need to be adjusted over time as disease impacts change.

Management options differ between stands without SOD and stands that have already been affected by SOD (table 2-3). The management options in table 2-3 are based on a considerable body of scientific data and practical experience. They represent the best management practices currently available. However, research into these management practices is ongoing. Check the sudden oak death website (http://www.suddenoakdeath.org) for updates on research and management recommendations. Detailed technical descriptions of these methods are listed in Part 3.

Table 2-2—Stand characteristics, information needs, and management objectives associated with progression of SOD

Stand characteristics:	◄Before: No SOD in canker hosts	♦During: SOD disease levels increasing	►After: most or all susceptible trees infected or dead
	Phase in SOD epidemic
Percentage of canker hosts with SOD	0	Variable, 0 to over 50%	High - 50 to 100% of at-risk hosts
P. ramorum present in stand	no	yes	yes
P. ramorum symptoms in foliar hosts such as bay	no	yes	yes
Primary management information needs:
Proximity to known P. ramorum	+	—	—
Likely impact if P. ramorum is introduced	+	—	—
Treatment priority (see table 2-7)	+	+	+
Current distribution of SOD across site and location of noninfected canker hosts	—	+	+
Failure hazard potential	—	+	+
Fuel loading due to dead trees	—	+	+
Restoration objectives	—	—	+
Site capabilities for restoration	—	—	+
Existing regeneration	—	—	+
Factors constraining restoration	—	—	+
Main management objectives: more “+” symbols indicate higher relevance/importance. "—" indicates low priority or not applicable
Preventing P. ramorum introduction	+++	+ (other strains)	+ (other strains)
Protection of noninfected canker hosts	++	+++	— (higher if noninfected hosts still present)
Minimize P. ramorum inoculum production	++	+++	— (higher if noninfected hosts still present)
Minimize hazards associated with SOD-killed trees	—	+++	+++
Restoration	—	+	+++

Table 2-3—Management methods to prevent or reduce disease incidence and severity

Methods	Targets / variants	Mgmt obj¹	SOD impact stages	Notes
Exclusion of infested plant material	Nursery stock	Prevent	◄♦►	Also important for exclusion of other soil-borne Phytophthora spp. such as P. cinnamomi
Leaves, plant debris	Prevent	◄♦►	Includes both intentional movement (e.g. green waste transport) and inadvertent transport (e.g., debris in equipment such as chippers)
Firewood	Prevent	◄♦►	Freshly cut wood with attached bark poses the greatest risk
Exclusion / sanitation	Soil	Prevent	◄♦►	P. ramorum and soil-borne Phytophthora species can be moved on tires, shoes, and equipment, mainly during wet conditions
Water	Prevent	◄♦►	P. ramorum spores are common in streams that drain infested areas
Bay removal	Localized removal	Prevent Minimize Protect	◄♦►	Reduces SOD risk of individual oaks by increasing distance from bay foliage
Area-wide removal	Prevent Minimize Protect	◄♦►	More efficient than localized removal if bay are relatively small and total bay cover is low
Bay canopy thinning/ raising	Minimize	◄♦►	Reduce bay foliar disease potential and inoculum production where complete bay removal is not practical
Targeted removal of highly susceptible bays	Minimize	♦►	Aim is to slow the seasonal epidemic by removing trees that show most disease carryover and high susceptibility
Remove climbing poison oak		Minimize	◄♦►	Primarily done with other disease management treatments (and with caution!)
Avoid pruning / wounding prior to wet season		Protect	◄♦►	Wounds have increased risk of infection for 4 months
Phosphite application	Individual tree treatment	Protect	♦►	Primarily used on selected individual high value trees. For tanoak stands, block treatment may be more effective.
	Block treatment²	Minimize Protect	♦►	Preferred approach for tanoak stands to protect trees and reduce inoculum production in treated block
Removal of understory tanoak		Minimize	◄♦►	Primarily used in conjunction with block treatment of tanoak with phosphite

Prevent = Prevent P. ramorum introduction. For 'during' and 'after' SOD impact stages, this refers to preventing introduction of additional P. ramorum strains

Minimize = Minimize potential for P. ramorum inoculum production

Protect = Protect healthy canker hosts

¹Management objectives related to treatment methods.

◄ = SOD impact stage is 'before'

♦ SOD = impact stage is 'during'

► = SOD impact stage is after (if some noninfected canker hosts are still present).

²Block treatment refers to treating all trees within a stand or in a contiguous area of forest.

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