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The
spores of fungal needle cast diseases of conifers infect
needles when the humidity is high and the needles are
wet. The most severe infections
usually occur on the bottom half of the tree and on the
shaded, northern side. The diseases are most severe at
these sites because water tends to remain on the foliage
for long periods, and this moisture favors spore
germination. Dense foliage dries slowly and increases
within tree spread of the disease from branch to branch.
Tree-to-tree spread is increased by close spacing of
trees that allows rain to splash spores from diseased to
healthy trees.
Two major diseases of pine are
Lophodermium
needlecast of Scotch
and red pines and Cyclaneusma or Naemacyclus needlecast of
pines.
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Lophodermium causes needles on infected trees to turn brown
in the spring. It may be confused with winter burn which will cause a uniform
browning of the needles and is most common on the windward side of the
tree. Lophodermium usually damages the lower branches of the tree
while the upper foliage remains green.
The needles are dropped or
"cast"
in June and July. Infection occurs when the spores are released to the
air starting in July and carrying on through the fall.
Needles infected with
Lophodermium will form shiny, football-shaped,
black fruiting bodies that may be found on fallen needles. In the spring,
infected needles form brown spots with yellow borders appear and enlarge.
The needle turns yellow and then brown by May or June.
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Since this is a
fungal disease, the key factor is moisture and how
long it sits on the needles before evaporating. So,
things like placing the plants in an area where
there is good air circulation can help. Ironically,
not pruning evergreens so that their foliage does
not get thick and lush like a Christmas tree. Yes,
those trees are pruned yearly but they are usually
cut down when they are 5 or 6 years old. Also,
Christmas tree growers often have to use
fungicides
to prevent their trees from getting
needlecast
diseases.
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Control:
Most fungal diseases of conifers can be partially controlled by
several cultural practices.
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Avoid planting in low areas, depressions or shady sites where
soil moisture, humidity and dew tend to remain high for prolonged periods.
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Plant so that air can circulate freely around trees. Avoid dense plantings.
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Control
weeds and tall grasses so that weed growth does not favor
the build-up of humidity and moisture around the lower branches.
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Avoid drought sites that stress trees. Serious infections of tip blight
and cankers are often associated with poor sites.
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Maintain tree vigor by watering during the periodic droughts of summer.
Early spring fertilization can help a diseased tree recuperate.
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Buy only clean and healthy nursery stock to reduce the chance of bringing
disease to your landscape. Remember that most needle casts are spread by
rain splash, so distance of spread is limited.
Lophodermium needle cast is spread by wind borne rather than
rain-splashed spores.
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Of course, always avoid planting young trees near older, diseased
plantings, windbreaks or woodlots.
Chemical Control:
For Lophodermium needle cast disease, apply a
labeled fungicide starting in late July. Repeat the applications every 10
to 14 days through September. |
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Note: We
have provided some general information and
observations on this topic aimed at the home
gardener. Before you take
any serious action in your landscape, check
with your state's land grant university's
Cooperative
Extension
Service for the most current,
appropriate, localized recommendations. |
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