Posted March 31, 2005: If you have a diverse operation
and are good to the soil, insects shouldn’t have a prohibitive
impact on your flowers. That’s the skinny from Part
1 of this two-part series. In other words, you don’t need
to be an entomologist to successfully grow and sell specialty cut
flowers on a small farm. But some knowledge of the good guys and the
bad guys, and keeping a close watch on your flowers, is important.
It can be educational and kind of fun, too (as long as the insects
you find are not appearing in record numbers).
Lots of catalogs have magnifiers that let you see the tiny insects
up close and personal, whether on plants or sticky traps (one is
Gempler’s at www.gemplers.com).
There are some good books out there with pictures of various stages
in the insect’s life cycle, too. Our new favorite is The
Ultimate Guide to Backyard Bugs, Garden Insects of North America
by Whitney Cranshaw. Penn State College of Agricultural Sciences
(as do many ag schools around the country) has a booklet entitled
“Managing diseases, pests and plant growth in Greenhouses”.
It's good outside the greenhouse, too, has good insect/disease descriptions
(but no pictures) and you can ignore the heavy chemical info. (Available
by calling, toll free, 877-345-0691; $9, plus $5 shipping/handling.)
So, without letting the following get you paranoid (because as
we said above, flowers aren’t that difficult when managed
well), here are some tips on . . .
The biggest problem insects
APHIDS -- Aphids
can be winged or wingless. They develop wings as numbers in their
colonies increase so they can move on to less populated areas and
wreak further havoc on your flowers. They are generally small, according
to Penn State’s booklet, 1 to 3 mm, and soft bodied. Caught
on yellow sticky cards, their front wings usually have two parallel
veins close to the outer edge which ends at a dark, thin part. Their
legs and antennae are long. Their color varies and as they get bigger,
they shed their exoskeleton which can be found on leaves or stuck
in their sticky secretions. Penn State says the insects “feed
by inserting their stylet-like mouthparts through plant tissue directly
into the phloem and removing plant sap. Feeding can lead to plant
stunting and deformities.” When you have a lot of them, they
look like a yellow, sticky mess all over your flower stem, leaves,
bud. The sticky secretion is called honeydew, which can be a growth
base for sooty mold.
That’s not all. Aphids are responsible for transmitting some
60 percent of all plant viruses on ag crops worldwide. Why are they
such a problem? Females give birth to live offspring, three to 10
a day, that immediately start to feed. They don’t need to
mate, so each female gives birth to MORE females. Within a week,
the offspring are ready to reproduce.
“With aphids, if I can be patient, nature often helps,”
says Steve Bogash, regional Extension commercial horticulture educator
in Central Pennsylvania -- if the problem isn’t too severe.
“I was all set to get out the spray for an aphid problem at
home and didn’t get around to it. Then I saw lots of lady
bug larvae -- which generally will take care of the problem.”
Byczynski says she occasionally sees some aphids early
in the season -- greenhouse ranunculus seem especially susceptible.
“They are easily controlled by insecticidal soap,” she
says. Insecticidal soap kills by disrupting membranes. Horticultural
oils can also be effective, killing by suffocation. Organic growers
need to check each product with their certifying agency/OMRI manual,
because not all organic pesticides are created equal and while some
are allowed, others are restricted.
Critical to aphid control is sanitation. Keep an eye on flowers
before problems develop. Start inspecting plants at the lower leaves
upward. And get rid of weeds near any problem spots that develop.
Biological controls can be very successful, especially in a greenhouse.
Lady beetles (Hippodamia convergens) sold as adults can
clean up bad problems. They also feed on other soft-bodied insects
like thrips. Lacewings (Chrysoperla rufilabris), sold as
eggs or larvae, also feed on thrips, spider mites, mealybugs and
scales. Predatory Midges (Aphidoletes aphidimyza) sold
as an adult for greenhouse release lay eggs near aphid colonies
where the orange larvae can then feed on sticky insects. Aphelinus
abdominalis, a type of wasp, parasitizes aphids--laying eggs
on their bodies, killing them--and eats the ones left unparasitized.
As Bogash says, most biological controls do better with a sanctuary
in which to stick around. When released in the greenhouse, they’ll
quickly go to work, putting on quite a show. But as the number of
aphids diminish, the good guys may also disappear.
THRIPS -- Adults
are found in blossoms, the larvae on leaves and deep in buds. Since
they feed on all of the above, as leaves and flowers grow, they
may look damaged, have a silver cast or appear streaked. Often black
specks of excrement can be seen where the thrips fed. Thrips are
tiny insects, just 1 to 2 mm in length with narrow bodies and fringed
wings, and colors vary from straw-yellow to brown.
To find them hiding in flowers, try the old trick: tap blossoms
over a sheet of white paper. This will dislodge them and, if you
have a bunch, you’ll see what looks like black pepper on the
paper. Penn State says the western flower thrip is the most likely
to hit floral crops, particularly in a closed environment. And it
doesn’t stay in the West, by any means.
Thrips are especially attracted to blue sticky traps, but they’ll
also find the yellow traps. Look for the tiniest insect on the trap,
and you'll see thrips with their wings folded over their abdomens
sticking to the trap--they put up no struggle. (Don’t say
‘aw’ until you’ve seen the damage they can do.)
They appear spindle shaped with protruding wings. Hairs line the
edges of the wings and they sport V-shaped antennae. Thrips love
marigolds and can hit lisianthus in a wet year.
The best controls are good sanitation and a weed-free zone. Early
detection is important because they spread various diseases such
as Tomato Spotted Wilt Virus. Dr. Stanton Gill, with Central Maryland
Research and Education Center, Maryland Cooperative Extension recommends
Amblyseius cucumeris, tan-orange predatory mites, as a
good biological control. Each predatory mite can consume up to 10
thrips per day and will survive on spider mites should you run out
of thrips (more on spider mites below). Orius insidiosus,
minute predaceous pirate bugs, are good beneficials, too, Gill says.
SPIDER MITES -- Usually
found on the undersides of leaves, especially near greenhouse heaters,
vents and doors where it’s warmer and dry. Yep, they are a
problem in hot and dry periods--they love water-stressed plants.
Early sign of mite feeding is yellowish-white speckles on the upper
side of the leaf as the chlorophyll is destroyed. Eventually, as
populations increase, the whole leaf turns yellow.
Penn State says the mite, specifically the two-spotted spider mite,
are minute arthropids with the largest adult female less than a
millimeter in size. The body of the adult female and most immature
stages is oval-shaped and usually appears light yellow to green
with two large dark green spots on either side. All stages have
eight legs except larval, which has six. Damage is caused by larvae
nymphs and adults piercing the plant cells and sucking out the contents,
leaving those tell-tale spots. Females lay eggs on the underside
of leaves in fine webbing that the mites constantly produce. Now
hear this: Each female can lay more than 100 eggs in a lifetime.
Eggs can hatch in three days. Since they don’t have wings,
sticky traps can’t catch them.
What to do? Don’t let weeds build up around your flowers
and don’t let plants get water stressed. A good crop rotation
helps, too. It’s harder in dry years, obviously. Bogash says
spider mites can be a problem in low tunnels. He recommends using
an insecticidal soap. Biological controls include Phytoseiulus
persimilis, predatory mite; Feltiella acarisuga, Predatory
Midge; Mesoseiulus longipes and Neoseiulus fallacis.
LEAFHOPPERS -- Are
small wedge-shaped insects that hold their wings slightly out. They
pierce plant tissue and suck sap, weakening the plant, and happen
to carry viruses. The best protection is protective covering (Reemay
or agribon fabric) over hoops. Aster leafhoppers, which cause the
dreaded aster yellows disease, are green yellow with six black spots
and they grow to about 1/8th of an inch so you can barely see them.
Both insecticidal soap and hot pepper wax are said to control leafhoppers.
Gill says neem will help control heavy infestations.
BEETLES -- Good sanitation
and crop rotation are important steps in controlling beetles. We
often just hand-pick them or squish them early in the season before
they get to be a problem. Japanese beetles are slow to get up in
the morning, so going out with a bucket of soapy water and flicking
them in works wonders. Gill recommends neem for large problems.
It represses the insects’ desire to feed. (And don’t
forget the guineas! See
Part 1 for more on using guineas.)
CATERPILLARS -- Caterpillars,
immature butterflies and moths including armyworms, cutworms, leaftiers,
leafrollers and loopers, have many natural enemies and are damaging
only as larvae. The natural enemies include parasitic flies and
wasps, damsel bugs, minute pirate bugs and more. Usually, caterpillars
aren’t a major problem for flowers. If populations get out
of control, and holes are being chewed in leaves (and large amounts
of excrement are seen on foliage) there are three popular methods
to fight back.
1. Find the buggers and pick 'em off.
2. Apply the microbial insecticide Bacillus
thuringiensis (Bt) will paralyze and destroy the insect’s
gut wall cells, but the insect must ingest the Bt, and it may
take up to three days for it to die as it chews away. Bt is sold
under several trade names. Again, check the OMRI listing for allowable
3. Use the popular biological control, richogramma,
an egg parasitoid. The tiny wasps lay their eggs in the eggs of
caterpillars. A new wasp emerges from the parasitized egg rather
than a new caterpillar.
Garlic sprays and hot pepper wax are getting a lot of press; garlic
for repelling insects (Bogash says it can deter bigger pests like
rabbits and groundhogs until they get used to the smell), and hot
pepper wax for killing a number of insects from aphids and spider
mites to thrips and leafminers. Garlic spray (garlic oil and water)
is said to keep insects off plants and the key is to use it as a
repellent spray on the plant before the bugs arrive, to keep insects
from ever finding a home. A variety of hot pepper products are on
the market. Or you can make your own (see sidebar for a common recipe).
Learn your beneficials
You probably knew lady beetles are your friends. But did you know
other predators, like ants and wasps, collect insect prey to feed
their developing young? Did you know fireflies do more than light
up the night -- most are predators of slugs, snails and worms, according
Insects of North America. The book even points out that some
stink bugs are good. The Twospotted stink bug “specializes
in beetle larvae such as the Colorado potato beetle” and the
spined soldier bug primarily feeds on caterpillars.
Most ground beetles develop as predators. Soldier beetles can be
important predators of aphids, mealybugs and other soft-bodied insects.
Rove beetles are predators of insects found in soil. Even paper
wasps feed their young on insects. (But, I can tell you first hand
how aggressive they are in defending their nests, which they love
to build inside high tunnels in places you don’t tend to see
until it’s too late. Needless to say, they are no friends
of mine!) There are many, many more. So know before you squish or
you may be destroying a friend.
While there are pesticides and insecticides approved or allowable
on a restricted basis by the Organic Materials Review Institute
(OMRI) for certified organic growers, they should be used only as
a last resort. Bogash advises keeping records of problems and scouting
plants to discover pests before they take over.
All in all, if you use a reasonable crop rotation and have an awareness
of insect problems that could occur, Bogash says growing
cut flowers is nothing you can’t handle. I completely agree.
Flower diseases--who, what, when,
where and why.