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Extension > Garden > Diagnose a problem > What's wrong with my plant? > Evergreen Trees > Spruce > Entire canopy is thin and growth is slow

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Spruce > Whole tree> Entire canopy is thin and growth is slow

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  • Image: Rhizosphaera needle cast 1
  • Image: Rhizosphaera needle cast 2
  • Image: Rhizosphaera needle cast 3

Rhizosphaera needle cast
Rhizosphaera kalkhoffii

  • Infected needles turn brown or purplish brown late in winter or early spring
  • Needles at the branch tips remain green, while older needles closer to the trunk of the tree become discolored
  • Tiny black dots can be seen with a hand lens on infected needles
  • Discolored needles fall off mid summer; tree looks thin and bare
  • Damage typically starts on the lower branches and moves up the tree
  • Most common on young Colorado blue spruce, but infects all spruces
  • More information on Rhizosphaera needle cast
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  • Image: Armillaria root rot 1
  • Image: Armillaria root rot 2
  • Image: Armillaria root rot 3

Armillaria root rot
Armillaria spp

  • Infected trees have poor growth, dead branches in the upper canopy, browning needles, may produce an abundant crop of cones, and eventually die
  • Clusters of honey-colored mushrooms may grow at the base of the tree in fall
  • Flat white sheets of fungal mycelia (mycelia fans) grow between the bark and sapwood at the base of infected trees
  • Thick black, shoestring-like fungal strands sometimes grow in a net on infected trees and in the soil around the base of the tree
  • The base of the tree just below the soil surface may be encrusted in resin
  • Wood is decayed, white, soft and stringy and may extend from the base of the tree well up into the trunk; trees frequently break or fall over in storms
  • More information on Armillaria root rot
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  • Image: Tomentosus root rot 1
  • Image: Tomentosus root rot 2
  • Image: Tomentosus root rot 3

Tomentosus root rot
Inonotus tomentosus

  • Heartwood of infected roots and trunks is initially reddish brown
  • As infection continues white pocket rot develops; decayed wood has elongated pockets or pits, and may appear honeycomb-like in cross section
  • Infected trees have reduced growth and thin canopies, produce large amounts of cones and eventually die
  • Infected trees frequently break or lodge during storms
  • Mushrooms that are velvety brown above and porous and buff colored below appear around the base of the tree in late summer
  • More information on Tomentosus root rot
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  • Image: Eastern spruce dwarf mistletoe 1
  • Image: Eastern spruce dwarf mistletoe 2
  • Image: Eastern spruce dwarf mistletoe 3

Eastern spruce dwarf mistletoe
Arceuthobium pusillum

  • Witches’ brooms, a clump of small weak branches arising from one point on a larger branch, form in infected trees
  • Needles within the witches’ broom remain green, needles on the rest of the tree yellow and fall off, typically from the top of the tree down
  • Short (1/2 to 1 inch) brown to orange dwarf mistletoe stalks can be seen during the growing season but fall off after seed dispersal in August or September; this occurs only after 4 to 5 years of infection
  • Most common on black spruce in northern Minnesota; white spruce are also very susceptible
  • More information on Eastern spruce dwarf mistletoe

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