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When plants die, be sure of the cause before
We had 17 arborvitaes and lost all of them. They were
five years old and had been healthy up to last fall, when I noticed
a slight yellowing and an overall "not looking so good." I had them
deep root fed at that time and in the spring, but noticed a lot
more dead and dropping branches. In less than two weeks they were
I took a branch to the local nursery, which diagnosed
spider mites. Unfortunately it was much too late to save them, and
six hemlocks planted at the same time were about half gone. So I
ripped everything out and replanted.
Now I wonder what to do with the new arborvitaes and
sandcherries. Do I start spraying, since I am sure that mites are
on the other bushes, junipers which I am treating with Isotox? Or
will that harm the new bushes? Should I use a high-pressure water
spray on the new ones, since I read on your website that regular
water sprays can take care of mites? I really don't want to go
through all of this again.
Your frustration is understandable, yet you may be heading for
another loss by leaping at the first villain you see. Take a step
back to look at how several basic principles of pest management fit
into your situation:
1) The presence of a pest (insect, mite or disease) does not
mean it's a primary problem. Many pests are secondary to other
issues; some occur or proliferate only on plants already weakened
by other factors.
2) When all or many of one type of plant on a site develops a
problem, review that species and variety to be sure it is right for
3) When multiple species on a site are beset by a single pest,
look for overall environmental problems.
If your arbs had died while other plants thrived, I'd say stop
planting arbs. But hemlocks and junipers struggled, too. There may
be something there that predisposes for mites, allows them to move
in and multiply.
Mites like dry heat. They kill plants gradually, not as primary
agents but contributors. So I'm nearly certain they are not the
sole reason your plants died, not so quickly and with damage
beginning and ending in cool, mite-unfriendly weather.
Mites are ever-present but often rise to problem levels on
plants weakened by drought. Shady, dry conditions are a double
whammy. A plant stressed by drought and low light can't make enough
energy or find enough water to keep its own systems running, let
alone make the extra it needs to replace what mites draw out.
Most of the years your first arbs were in place were drought
years, so they may have still needed pampering when you thought
they were a done deal by year two or three. Even in the best
conditions plants can take years to replace roots lost in
transplant and become truly self sufficient. Larger plants
establish more slowly than smaller ones -- figure a year of
recovery time for each inch of trunk diameter. So your plants may
have been stressed for years, showing it in ways invisible to you
such as lower than average growth rate until they developed severe,
unmistakable symptoms at the bitter end.
Review your site to see if it offers everything an arb could
Is there at least six hours of sun each day? If not, prune
overhanging trees or shift the shrubs to improve the light.
How does the soil drain? Arbs, hemlocks and junipers all need
well drained soil. You have that if an 18 inch deep hole there,
filled with water, will drain completely in less than 24 hours.
They need loose, well-aerated soil, too. If the soil beyond the
planting holes is hard packed, loosen it and keep it mulched.
How do you water the site? Arbs and hemlocks need steady
moisture. They thrive where soil is cool and moist, never soggy,
hot or dry. On slopes or hard packed soil, let water trickle so it
can seep in. Be certain an area needs water by feeling the soil,
don't rely on a timer or wait until plants show wilt.
Is it windy? That's stressful to arbs and hemlocks. Plant
wind-loving species like sandcherry upwind, to take the edge
Finally, protect this big investment. Hire someone to assess the
plants' health, now and a year from now.
If a plant had problems with holey leaves last
...buy a magnifier and look at a few of its leaf undersides now.
Many pests are just beginning to feed . Deal with them now before
leaves become irreversibly damaged. Also, soft solutions such as
hosing with plain water and hand-squishing work better in a pest's
Green thumbs up
to on-site plant care recommendations. Much better than
diagnosis from a specimen, which require the diagnostician to rely
on secondhand reports of the site and history -- factors that
usually have more bearing on plant trouble than a resident
Green thumbs down
to hiring any plant care service without checking references.
Ask for telephone numbers of satisfied customers whose contact with
the service happened at least a year ago. Then ask about long term
results when you call to confirm the referral.
Originally published 6/14/03
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