11-04-2003, 04:08 AM
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rhododendron problem
In article ,
(Steve Henning) wrote:
"Andy" wrote:
Our rhododendrons have a fair number of leaves browning along the edges,
wilting, and curling up. On some of these leaves the brown is combined with
white spots. I live in Rhode Island and we have had a very tough
winter--snow forecast for tomorrow, as a matter of fact. Any ideas what the
problem/treatment is?
Wind and cold damage is indicated when the edges of the leaves become
distorted and turn brown.
As a footnote only: Rhodendron hippophaeoides' leaves brown & curl during
harsh winters as a healthy process, & then return to green & unfold in
spring as though nothing happened. Though hippophaeoides is one of the
"least rare" species-rhodies on the market, & has been gardened for almost
a century, & should be able to pass along its trait of extreme
cold-hardiness, it hasn't been used in any important hybridazation
programs, which is most curious. I have a theory (but no no way of knowing
if it's true) that hybridizers who tried it in the past got plants that
browned & curled in winter, which would make such a hybrid less marketable
even though there's nothing wrong with it.
-paghat the ratgirl
This occurs frequently in plants that may be
in a colder climate than recommended or in a location with severe
exposure. Note, boron poisoning will create the same symptoms.
If a leaf has brown areas with white spots, it probably has a local
fungal infection of Pestalotia leaf spot. This is seldom controlled with
fungicides and is best mitigated by good sanitation and avoiding
excessive moisture.
There isn't much you can do now except to protect the plants from
further stress. You may be able to prevent this from happening again.
Some rhododendrons can tolerate severe winter conditions while other can
not. The main problem is desiccation of the foliage when the ground is
frozen and sun and wind attack the leaves. There are four solutions:
1: cold-resistant varieties of plants,
2: winter wind breaks
3: winter sun shades
4: chemical antitranspirants
To insure that a plant has the ability to make it through the winter, it
must be dormant. Dormancy is a normal process in which the plant goes
into a rest state during the winter. Dormancy is caused by a number of
things including short days, low temperatures and drought. Several
things can break or prevent dormancy.
* Too much nitrogen fertilizer after mid summer will keep a plant in a
growth state when it should be going into dormancy.
* Warm weather spells during the winter can break dormancy in a plant
that has gone dormant.
* A warm fall followed by a sudden winter, can expose a plant to the
cold before it has gone dormant.
* Too much light such as being planted under a spot light that is kept
on all night.
--
"Of what are you afraid, my child?" inquired the kindly teacher.
"Oh, sir! The flowers, they are wild," replied the timid creature.
-from Peter Newell's "Wild Flowers"
See the Garden of Paghat the Ratgirl: http://www.paghat.com/
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