Why Do Bad Things Happen
to Good Azaleas?
Bad, Bad Fungus
Phytophthora cinnamoni Root Rot
Plant foliage appears wilted,
even in the early morning. The fungus plugs up the conductive tissue in
the roots, preventing mositure from reaching the upper parts of the plant.
Not only azaleas, but also dogwoods, pieris, yews, camellias, laurels,
junipers, blueberries, and pines can suffer from this fungus. There is
no cure; remove all parts of the infected plant, and dispose of them. Do
not plant any other susceptible plant in that area until the ground has
been sterilized.
Root rot thrives in a wet area
because the fungus only becomes infectious in water-saturated soil. The
best preventative is to plant only in well-drained soil. If you have wet,
heavy clay or upland silt which stays soggy, yet you want to plant azaleas
there, build a raised bed.
Ovalinia azalea Petal Blight
Here's a problem which can show
up among the late-blooming azaleas. Petal blight fungus can transform azalea
flowers into a brown slimy mass if there is warm, wet weather at bloom
time. Infected flowers turn brown and fall to the ground, developing spores
the next spring.
Toxin-lovers answer: Spray the
flower buds just as they begin to show some color with Triadimefon. If
the weather stays warm and wet, spray them again when the flowers open.
Toxin-haters answer: Pick off
all the brown flowers and dispose of them. Cover the fallen flowers with
enough mulch to cover them completely, 1-2 inches.
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Bad, Bad Insects
Lacebug (Stephanitis)
Bad News
These are awful little bugs!
They came from Asia, where natural predators kept them from sucking all
the chlorophyll out of everything. They have become a great problem in
the northeast USA, including Howard County. Lacebugs are tiny, fly-like,
sucking insects that hide under a leaf and suck out chlorophyll. And they
hatch four times a year, so you have to check for them in May, June, July,
and August. Ick. Look for whitening of the leaves and lots of icky little
bugs underneath.
Toxin-lovers answer: Acephate,
applied in May. Good for a year.
Toxin-haters answer: Insecticidal
soap, 85% effective, applied every month as a spray. Be sure to get the
underneath part of the leaf.
Good News
U.S. Department of Agriculture
experts believe that since the natural enemy of the lacebug, Stethoconus
japonicus, has now been discovered in the USA, this predator
will play a very significant part in reducing the damage done by lacebugs.
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Bad, Bad Animals
Rabbits are fond of azaleas,
but fortunately rabbits are not very tall and constitute a menace only
to young or dwarf azaleas. They tend to nibble off twigs rather than gnawing
the bark off major limbs.
Deer, especially hungry deer
whose forest clearings and meadows were just replaced with a housing development,
can develop an appetite for azaleas too, particularly during dry or bleak
winter weather.
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Bad, Bad People
Mulches which duplicate the
native habitat of azaleas in woodlands help maintain soil temperature and
moisture levels. Loose, coarse mulches such as pine needles, wood chips,
oak leaves, and shredded bark are ideal. Proper mulching is second only
to watering in keeping azaleas healthy and attractive.
Too much mulch, however, can
lead to root damage and to death. Anything which is over 3 inches deep
or packs down tightly can cut down the oxygen exchange between the roots
and the air. The symptoms of over-mulching resemble other root damage:
yellow leaves, poor growth, dieback, and death.
"Not only is over-mulching a
waste of mulch, but it is rapidly becoming the number one cause of death
to azaleas, rhododendrons, dogwood, andromeda, boxwood, mountain laurel,
hollies, cherry trees, ash, linden, spruce, etc. Repeated applications
of mulch cause suffocation of the roots of shallow rooted species."
From Nurseryman's News
Dr. Francis R. Gouin Chairman of the Department of Horticulture University
of Maryland
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