Beech ____ Bark ___ ______ Disease__ in ______ Ontario Biology, Range, Impacts & Response John McLaughlin Ontario Forest Research Institute Sault Ste. Marie, Ontario
Richard Wilson Forest Health & Silviculture Section OMNR, Sault Ste. Marie, Ontario Beech Bark Disease Workshop Finch, Ontario November 17, 2011
What is Beech Bark Disease? A disease associated with two non-native causal agents: beech scale (Cryptococcus fagisuga) & Neonectria faginata …and rarely N. ditissima syn. Nectria galligena (insignificant in our Ontario survey…only 4 of 99 samples were N. ditissima)
Where did it come from? History (origin) beech scale introduced from Europe to the Halifax area ~1890 by 1930s tree mortality from BBD was observed in the Maritimes and Maine BBD in Quebec - 1965 early report of scale in Elgin Co. in1966 first report of tree mortality north of Toronto in 1981, but fungal pathogen not confirmed at that time.
Epidemiology (infection & spread) The infection process – beech scale The outer cells of the beech bark are altered by the scale feeding in such a way as to make them receptive for infection by the N. faginata. Reports of lag times between scale infestation and appearance of fungal infection range from ~2 to 10 years.
Lifecycle of the beech scale 1. Eggs hatch on beech tree (~mid-summer); 2. Nymph, or “crawler”, finds suitable location on tree and forces its tubular mouthpart (“stylet”) into the bark, and begins to feed; 3. Crawler then molts to immobile 2nd stage and produces wooly wax protective covering; 4. Second-stage crawlers overwinter and molt to adult stage in the spring; 5. Each mature adult scale (all are female parthenogenesis) lays 4-7 eggs in early summer.
A predator of beech scale The twice-stabbed lady beetle (Chilocorus stigma) is a native species and a predator of beech scale. Both the adult and larval stages feed on scale.
Epidemiology (infection & spread) The infection process – fungal pathogen(s) N. faginata (or rarely Nectria galligena) infects bark cells altered by scale feeding; Pathogen colonizes a portion of bark as deep as the cambium, producing a canker; In fall the pathogen produces small, bright red perithecia which erupt through the bark; Infective ascospores are released from the perithecia during damp or rainy weather.
A parasite on a parasite! Nematogonum ferrugineum is parasitic on
Neonectria faginata! Unfortunately, this mycoparasitism does not occur often enough to be an effective bio-control.
Epidemiology (infection & spread) Spread (natural) tiny crawler stage can move from tree to tree on wind currents; on birds, insects mammals? Spread (assisted) on firewood & logs, especially during the crawler stage (mid-summer to late fall)
Stages of Spread The Advancing Front …is characterized by… arrival and colonization of trees by scale alone
Can scale damage trees? On some sites scale has been present for many years but BBD has not developed Observed damage ranges from superficial, localized necrotic spots, “pimples”, to deep bark cracks Heavy scale feeding is a stress that can contribute to decline of beech trees suffering other stresses such as root disease or drought.
Stages of Spread The Killing Front …is characterized by… rapid build-up of scale infestation; abundant Neonectria infection and canker development; heavy levels of tree mortality.
Stages of Spread The Aftermath Zone …is characterized by… lower scale populations; residual, defective and declining trees; perhaps a few resistant/ tolerant trees.
Range of BBD in Ontario
BBD research plots
Beech Bark Disease Resistance/Tolerance Resistance to BBD is defined as resistance to the scale insect … no scale no BBD 1 – 4% of beech trees exhibit resistance Tolerance? - Susceptible to scale but resistant to the fungal pathogen, N. faginata. - Limited susceptibility to N. faginata. Able to limit the impact of infection with chemical and callus barriers.
Resistance
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Disease tolerance? Often, beech trees appear to be able to wall off infections with callus tissue and continue to grow. The contained cankers may, or may not, extend to the cambium. Many are superficial. Heavy scale feeding is a stress that can contribute to others such as drought.
How can we keep beech on the landscape? Role of science organizations: - further research into BBD epidemiology; - development of molecular tools to identify diseaseresistant trees. Role of forest owners/managers: - make maintaining beech in your forests a priority; - include identification of disease-resistant/tolerant beech in any stand surveys or studies; - conduct a specific survey to locate and georeference disease-resistant/tolerant beech.
How can we keep beech on the landscape? Role of tree markers: - report observations of scale and BBD; - retain and release healthier beech trees in affected stands; - specifically watch for disease-resistant/tolerant beech.
Tree 963… - large basal wound & internal decay, but - no scale - no BBD, … in a stand with lots of scale and BBD
Tree 964‌ - good form & crown, - no wounds or cracks, but - scale - BBD!
Best Management Practices On the Advancing Front 1. Identify, mark and retain resistant trees – no scale, or low level of scale among trees heavily infested; 2. Identify trees for salvage – remove trees heavily infested with scale, overmature trees, trees with rough bark, trees with obvious decay or defects (unless retained for wildlife); 3. Do not transport firewood or logs during the crawler stage (midsummer to late fall).
Best Management Practices On the Killing Front 1. Identify, mark and retain resistant trees – no scale, or low level of scale among trees heavily infested; 2. Salvage recently dead or dying trees, and trees with sunken lesions or patches of dead wood. Declining beech are rapidly invaded by secondary decay fungi and that can degrade wood in 2 or 3 years; 3. Prioritize harvest of heavily infested or cankered trees;
Best Management Practices On the Killing Front (cont’d) 4. Watch for development of beech thickets around dead trees and consider herbicide control. 5. Do not transport firewood or logs during the crawler stage (midsummer to late fall).
Best Management Practices In the Aftermath Zone 1. Salvage dead and dying trees; 2. Retain resistant trees – no scale, or low level of scale among trees heavily infested.
Best Management Practices Trees in urban and recreational areas 1. Trees with BBD often become hazard trees due to “beech snap” resulting from secondary decay fungi invading cankered areas. Removal is advised. 2. High-value trees can be protected from scale by: Physical control – removal of scale from accessible portions of the tree by high-pressure water wash; Oils – Application of dormant oil Insecticides? – None currently registered.
The rest of the workshop… - Field visit to look at various stages/ expressions of BBD; - on-site consultation regarding “best management practices”.