| Posted May 12,
2005: When you’re trying to do a good job of growing
those cut flowers for market, it’s hard enough keeping up with
Mother Nature and her whims -- you know, this year for us in the Northeast
it was weeks of no sun in early spring, followed by ‘August’
in April, warm weather and no rain -- and we’re not out of the
woods yet in mid-May (so please, no late
frost!) Throw in the pests (see two previous columns). Add the diseases,
and it can seem a little insane.
When it comes to flower diseases, just remember a couple of old
sayings: Sanity rules (sounds good whether it’s old or not),
and "an ounce of prevention...” you know that one. For
the beginning flower grower, or the seasoned market gardener, the
preventive stuff is the best way to keep disease at bay. That means
working with your soil to keep it healthy, using compost and cover
crops to add fertility and refresh the beds, using proper irrigation,
rotating crops, and selecting disease-resistant varieties, especially
for those flowers that can be a problem in your area. Trying to
keep a little ahead of the weeds can help, too, although I’ve
yet to meet a flower grower who doesn’t wind up apologizing
to visitors for weeds. (Especially me.)
We’ve had very few problems with disease on flowers at Pheasant
Hill Farm. We rarely even need organically approved disease fighters.
My flower partner and I are always checking, and if something is
fading or appears ill, it gets removed. Our main problem has been
powdery mildew on monarda and zinnias. Last year, we had pretty
good success using a milk spray (1 part whole milk to 9 parts water)
to ward off powdery mildew on the zinnias. This year, we’ll
start using the spray earlier, as a preventative. Since the leaves
are stripped anyway and that’s where the problem hits, the
flowers are saleable if the infestation isn’t severe.
About half of our China asters got hit with aster yellows last
year, and this year we’re going to keep them covered with
hoops and Reemay to try to keep the leafhoppers from turning them
to mush. (I have to say we had more than enough flowers from the
healthy plants last year.) We also had some rust problems in August
in our biggest high tunnel. Damage was done to the leaves of agastache,
dahlias and blue horizon ageratum. The lisianthus were unaffected.
This year, we’ll try test spraying some peroxide to see if
So we don’t consider those little problems -- with the thousands
of healthy flowers we sold -- real problems at all. We’ll
keep working on simple solutions. Those mysterious disease problems
will hit from time to time. You don’t have to be a professor
of horticulture to get through them. There are many good books with
pictures of diseases and detailed descriptions of their symptoms
and possible solutions. The internet has tons of information. If
you’re still not sure about a particular problem, contact
or visit your local Extension office.
All in all, says Steve Bogash, regional commercial horticulture
educator, Franklin County Cooperative Extension in Chambersburg,
PA, diseases on cut flowers are low on the problem scale. He says
it’s important to be observant, to catch any blips before
they become problems.
“Powdery mildew is one of the most irritating problems, especially
with zinnias, even with succession planting,” says Bogash.
But, he adds, if you use a reasonable crop rotation, the small grower
with diversified crops just shouldn’t have that many problems
Dr. Stanton Gill, with the Central Maryland Research and Education
Center, Maryland Cooperative Extension, agrees. In addition to powdery
mildew, bacterial leaf spot can also hit zinnias. But both men pointed
out that these, and other fungal diseases often don’t kill
the flowers. Just strip the leaves away and you can still sell those
flowers in bouquets or bunches.
Something as simple as watering the right way can help you keep
many diseases away, or from becoming serious problems. Using drip
irrigation, or watering plants at the base instead of sprinkling
or watering overhead can help you avoid botritis, alternaria and
bacterial and other leaf spots, powdery mildew and anthracnose on
flowers that are more susceptible to those diseases -- like zinnias
and snapdragons. (More on those diseases follows).
Keeping insects under control is important in disease control,
too, because they can spread viruses. And maintaining good air circulation
can help avoid some problems like powdery mildew and botritis.
Some Common Diseases
Alternaria -- A fungal
blight where leaves develop brown to black spots which enlarge and
develop concentric rings like a target. Lower leaves are usually
hit first. Spores are carried by air currents. Plant resistant varieties,
rotate crops or use a disinfecting solution before planting (see
Bacterial leaf spot below).
Anthracnose -- A
fungal disease that causes small seemingly dead spots with sunken
centers and raised borders. To control, rotate crops, buy disease-free
seed and don’t touch plants when they’re wet.
Bacterial leaf spot
-- Like alternaria causes spots on the leaves, but there is usually
a yellow spot around it. Along with powdery mildew, this hits zinnias.
Some growers recommend soaking seed in a mixture of 1 part bleach
to 4 parts hot water (100 degrees), soaking for 20 minutes. They
swear by it. Also, overhead watering encourages the problem.
Botrytis --A plant
pathogenic fungus and it’s everywhere you grow plants. The
disease it causes are gray mold or Botrytis blight. It hits many
types of plants. Botrytis starts out looking like a white growth
and turns gray as spores form. The spores are spread by wind or
water. Botrytis needs a food source or nutrients to invade a plant,
and this can come from old flower petals. With this food, the fungus
gets aggressive and heads for healthy tissue. High humidity or moist
conditions encourage growth of the fungus which is why greenhouses
are a favored spot. To control it, keep things clean. Remove dying
or dead leaves from plants and the soil surface and get it out of
the greenhouse or away from outdoor plants. It’s a concern
with lilies grown in crates. You’ll see it on the leaves,
white and spreading out round. Feeding drip irrigation through crates
to keep foliage drier and providing adequate ventilation help. Prevention
is easier than dealing with the problem, says one long-time grower,
who recommends trying a Bordeaux mixture (a combination of hydrated
lime and copper sulfate) or foliar compost tea for problems. Organic
growers needs to check the list of allowable materials, of course.
Damping-off -- Caused
by fungi in the soil. The seedling looks like it was burned at the
root level and die or seeds may rot before they germinate. Excessive
moisture, those days of no sun in spring, and overcrowding seed
flats encourage the disease, as does low soil temperature before
germination. To avoid problems, use good sanitation practices --
disinfect trays, keep greenhouse benches clean, etc. -- and use
bottom heat to until germination. We sprinkle milled sphagnum moss
lightly across the top of flats if overcast days linger. Remove
any plants from the cell that appear diseased, and if the entire
flat appears problematic, get it out of the greenhouse.
Powdery Mildew --
Miserable fungi that love many flowers, including zinnia, monarda,
phlox and several others. Mildew makes a white to grayish powdery
growth on leaves. Then black dots appear and produce spores that
the wind carries to other plants. It’s best to use preventive
measures before there is a problem, with either the milk spray mentioned
above, or a baking soda spray -- dissolve 1 teaspoon of baking soda
and a few drops of soap in 2 quarts of water and spray on plants.
Remove any infected plants.