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 it helps.
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 with disease.
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
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
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
-- 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
-- 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.
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
-- 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.
-- 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