|Table: Diagnosis and Control of Rhizosphaera Needle Cast|
|Pest Identification||Host Plants||Damage Symptoms|
|Rhizosphaera Needle Cast
|In the Midwest:
Colorado blue, white and black spruce
|Discolored older needles: Needles become mottled yellow in late summer,
then turn brown to purple-brown in late winter and the following spring, and drop off the
tree during the following summer and autumn.
Black, dot-like spore producing structures in stomata on infected needles (both green and discolored). These black structures typically appear in rows along the length of the needle, and they can be easily seen with a 10X hand lens.
Branch defoliation and dieback: bottom-up and inside out pattern within the tree.
|Inspect nursery stock carefully, and plant only healthy trees.
Look for discolored older needles. Black, dot-like spore producing structures within stomata on infected needles (both green and discolored). These black structures typically appear in rows along the length of the needle and can be easily seen with a 10X hand lens.
Defoliation and branch dieback on the lower portion of the crown.
Plant resistant spruce--Norway spruce. Do not plant susceptible species next to infected trees. Promote good air circulation by adequate tree spacing and weed control. Do not prune or shear trees when foliage is wet. Prune out and destroy severely infected branches (during dry weather). Rake up and destroy fallen needles.
|Description and Life History|
Description: Infection typically occurs on lower branches first and spreads in an upward and outward
defoliation pattern within the tree. Successive years of premature needle loss can kill individuals branches,
and in severe cases, entire trees.
Life history: The fungus overwinters on infected needles on the tree and also on fallen needles. Infected needles release spores of the fungus in late spring, during wet weather. The spores infect needles that are actively elongating or needles of any age that are senescent or stressed.
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