Disease

Needle cast and tip blight

Rhizosphaera, Dothistroma, Diplodia (Sphaeropsis) and others

Fungi that kill conifer needles or new shoots in wet weather. Needle casts work up from the lower branches over years; Diplodia tip blight stunts and browns the new shoots of older pines.

Signs

• Older needles turn brown or purple and drop, lower branches and inner needles first.
• Tiny black dots lined up in rows along dead needles (look with a lens).
• On pine, new shoots stunted with short brown needles, often with resin and black dots at their base.

What favors it

Wet weather, crowded and shaded lower branches, sprinklers wetting the needles, and stressed or poorly sited trees.

Prevention

• Space new trees for good air flow and keep sprinklers off the needles.
• Do not shear spruce; remove infected pine shoots in dry weather.
• Plant species that resist the local diseases, such as Norway spruce instead of Colorado blue spruce where Rhizosphaera is common.

Crops it shows up on

Evergreens & conifers (pine, spruce, juniper).

Often confused with

Sources

• Rhizosphaera Needle CastMontana State University Extension
• Diplodia Tip BlightMontana State University Extension
• Dothistroma Needle BlightMontana State University Extension
• Rhizosphaera needle castUniversity of Minnesota Extension
• Spruce: Rhizosphaera needle castWashington State University HortSense

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