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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