April 2022 - 23

PLANT HEALTH
a disinfestant, such as chlorine
products (like bleach and chlorine
dioxide), peroxides, and quaternary
ammoniums (such as GreenShield,
KleenGrow and Physan). They all
work in some instances, but the
quaternary products are overall
very effective and relatively safe on
plants, people, and metal. We would
not eat food from our bathroom
counter, right? Remember the right
disinfestant can prevent bacteria
and fungi and sometimes even
viruses from growing and can
even eradicate them from growing
surfaces like benches.
Use only new or throughly
cleaned pots, flats and other
containers. Wash and disinfest
using the products listed above.
We performed some simple tests
in cooperation with a nursery
operation to determine the actual
need for cleaning if a quaternary
ammonium soak was used on
recycled plug flats. The best control
was a thorough washing (cleaning)
followed by a 5-minute soak in a
quaternary ammonium at labeled
rates. Even higher rates used much
longer were not as effective as
when the flats were first washed.
NEW/HIGH-QUALITY
GROWING MEDIUM
I think it is always best to use
only new potting media. Do not add
native soil to any potting medium,
ever. Think about how potting
medium gets into a compost or
dump pile. The plants fail to grow
and are not salable (signaling the
possibility of a disease) or they are
simply overage.
If the potting medium has
already been through a growing
cycle, it is reduced and now
contains roots and at least lower
stems of the crop. Reusing potting
medium also exposes the new
plants to pesticides and fertilizer.
How can you determine the rate of
fertilizer to add when you do not
know what is already in the potting
medium?
Although every plant pathologist
will tell you to only use pathogenfree
seeds, cuttings, liners and
other materials, this appears to be
getting harder right now. Check all
AmericanHort.org/Cultivate
materials that you purchase when
they arrive and place tracking
numbers on them to determine the
exact source if a disease shows up
later (this is especially important
for seed lots).
If you have your own stock
plants, maintain them in a healthy
unstressed state. Take cuttings
from the tops of the plants to
facilitate rapid rooting and avoid
possible contamination. Clean
cutting instruments between
plants. Never use any plants with
symptoms on any part of the
plants; taking cuttings from a plant
that has symptoms on one area
but not another is not safe.
WATER MANAGEMENT
If you recycle water, consider
a water treatment. This water
has the same concerns as
reused potting media. Fertilizer,
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April 2022

Table of Contents for the Digital Edition of April 2022
