Association of an insect-fungal complex with red pine decline in Wisconsin
Red pine decline, characterized by an expanding circular area of dead and declining trees, is becoming increasingly prevalent in Lake States plantations. A 3-year study was conducted to determine whether any insects, fungi, andor soil parameters were assoctated with this syndrome. The root collar weevil-Hylobius radicis, the pales weevil-Hylobius pales, the pitch-eating weevil-Pachylobius picivorus, the red turpentine beetle-Dendroctunus valens and Hylastes porculus were significantly more abundant in declining stands than in healthy Pinus resinosa stands. These root- and lower stem-infesting insects consistently carried Leptographium terebrantis and Leptographium procerum.Higher soil organic matter, pH and K levels were also associated with areas of mortality. Intensive root sampling revealed high levels of root mortality, staining , infestation with Leptographium species and extensively grafted root systems in decking red pine stands. This advancing belowgound mortality precedes the aboveground symptoms of reduced radial growth, thin crown structure, and infestation by the pine engraver, Ips pini, and its fungal associate Ophiostoma ips. Colonization by the latter two species is ahvays associated with and/or responsible for ultimate tree death. A sequence of interactions among this complex of organisms and abiotic factors is proposed as the cause of red pine decline.
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