How To Recognize and Control Botrytis in the Home Garden
Botrytis or Grey Mold (B. cinerea) is the single
most common fungus in Mother Nature's arsenal. It is the primary attack
weapon to attack weakened plants or fading flowers in order to start
the recycling process.
So when you look at the grey mould on your plants, understand that this
is nature trying to recycle the nutrients in the plant to make them
available for other plants; it is part of the natural cycle of things
rather than a personal attack on your garden.
What does it look like?
The intial sign on flower petals is a small, light coloured
spot (sometimes surrounded by a maroon halo).
Under conditions that
fungus thrive in (moist, dark, no air circulation) then the fungus will
quickly expand into irregular shaped blotches that will cover every
Infected flower buds won't open (on all plants not just roses) and if
your flower bud won't open – suspect botrytis.
Stems might have slightly sunken lesions spreading down the stem from
infected flower buds.
This fungus also produces cankers on stems similar to other fungal
problems. It is not uncommon to see entire stems killed back. This is
particular true in susceptible varieties or plants where the conditions
are excellent for fungal problems and no controls are taken. Think
extended periods of cool, humid weather and you're looking at prime
fungal development on rose flowers.
How Did I Get It?
As befits this most common of fungus problems, spores are
lighter than air and are carried along on the air currents. If you
happen to have a flower that is badly infected and the fungus has moved
to the fruiting stage, moving the flower will produce a "cloud" of
fungal spores that is easily seen. Spores are common when the
temperatures are between 60 and 72F and the area is moist.
How Do I Stop It?
The number one control procedure is
sanitation. If you remove spent flower blossoms (called deadheading)
you'll be taking away the prime source of food for this fungus.
Clean up the garden in the fall. Botrytis overwinters on plant debris
and flower stalks.
Remove all spent flowers or petals from the ground. When you see peony
blossoms falling on the garden and quickly turning brown, you know
botrytis is doing its thing.
Remove dead flower parts.
Two You have to have good ventilation in your
There's little point in crowding plants so tightly together and
not expecting fungus problems.
Give plants the spacing they deserve so
they can grow properly without fighting for every inch of air space.
Air circulation dries plant leaves and flowers and dry conditions will
not support fungus.
Three As soon as you see problems,
Get out the
pruning shears and cut off the diseased flower parts.
A little remedial
pruning will go a long way to helping control the spread of the fungus.
Discard all infected flower parts into the garbage and do not compost
Four Do not water in the evening.
This allows water
to stay on plant surfaces overnight. This high humidity is excellent
for the fungus.
Water first thing in the morning so the water will
evaporate from leaf surfaces.
Five Have healthy plants.
Plants that are fed with
compost and compost
will have better immune systems than plants fed a high
nitrogen chemical fertilizer. Overfeeding produces lush, soft growth
that is a signal for fungal infestations and insects to attack the
Six Use Organic Sprays
You probably want to know what to spray
the plant with to stop the problem totally.
There are fungal fighters
in the environmental arsenal that will effectively knock back botrytis.
1) Lime sulphur is readily available at garden centers and this is
easily applied (although it stinks) and extremely effective.
2) There are now mixes entering commercial agriculture with other
fungus sprays. You spray a good fungus on your plant that attacks and
eats the bad fungus. These are not yet available on a home scale but
3) Trichoderma harzianum, with a brand name Root Shield Home and Garden
can be sprayed to help prevent Botrytis Blight. It is also very
effective in preventing root and bulb rots. This microorganism
colonizes plant tissue surfaces where it out-competes the bad fungi for
space on the plants. I have not trialed this material.
4) Neem oil is used for a wide variety of plant insect and fungal
problems and is highly recommended if used according to directions.
5) Make an spray of 1 tsp. baking soda and 1/4 tsp. horticultural oil
mixed in 1 qt. warm water. Add a few drops of liquid soap to help the
oil and water mix. Constantly agitate the sprayer while spraying to
keep the oil, water and baking soda in suspension and spraying equally.
6) I note that there is research out there that shows that the baking
soda and the hort oil can be used separately as well as in combination.
Do not use the same spray every time you spray.
Pick two or
three sprays and alternate them. This will help prevent the botrytis
from becoming resistant to your controls.
You'll need to spray every week or after rains to keep this problem in
But the biggest thing is your gardening skills.
Feed the plants
properly so they're healthy and keep your garden neat and botrytis
infections will slow right down.
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