In the late-winter chill in south Georgia, many of this
spring’s tender young plants
were nestled in the warm embrace of greenhouses.

"Greenhouses provide a protected, warm place for farmers
to get a strong, early
start on their crops," said Danny Gay, a plant pathologist
with the University of
Georgia Extension Service.

Commercial farmers and home gardeners alike depend on
greenhouse producers to supply
young plants for transplanting into fields or garden plots.
Cabbage, peppers, tomatoes,
watermelons and cantaloupes may be transplanted crops.

"Producers who provide greenhouse space to start those
crops off," Gay said,
"work hard to make sure the young plants stay
healthy."

Of the transplant crops, south Georgia is best known for its
melons. In 1995, Georgia
farmers grew almost 9 million pounds of watermelons and
cantaloupes, nearly all of them
started in greenhouses.

Many home gardeners count on greenhouses, too, for early
tomato and pepper plants.

But greenhouses can be as hazardous as they are protective,
Gay said. The problem is
that the best conditions for growing healthy seedlings are also
perfect for plant
diseases.

"Pathogens include disease-causing bacteria, fungi or
viruses," Gay said.
Many of these pathogens can virtually destroy an entire crop.

Greenhouse producers start protecting their fragile crops
even before planting by
buying certified disease-free seed.

The Georgia Department of Agriculture certifies seeds and
transplants based on
laboratory examination and inspection of growing sites.

Once seed is selected, greenhouse growers sterilize or
sanitize every surface in the
greenhouse. That includes walls, tables and ceilings.

Each planting tray, if it’s not new, gets the same treatment
to kill any
disease-causing organisms that could be present.

"Everything is either sprayed with a bleach solution or
steam-sterilized,"
Gay said. "These plants get the best chance at starting out
disease-free."

However, due to the nature of greenhouse conditions and the
methods producers must use
to grow transplants, Gay said, the danger still lurks.

Many disease-causing pathogens are so small and light, he
said, that even a light
breeze can carry them into a greenhouse and onto the seedlings
in it.

Greenhouse operators carefully water the tender young plants
with fine water sprayers
and then run fans to dry the foliage. If plants stay wet for 12-
14 hours, Gay said, the
chances of a disease outbreak increase dramatically.

"It’s exactly the moisture and temperature combination
these pathogens thrive
in," he said.

In other, less humid areas, greenhouse growers can open doors
or vents to circulate air
over the plants to dry the foliage fairly quickly. In Georgia,
though, humid outside air
may bring in the deadly organisms that cause the damage the
grower was trying to prevent.

Greenhouse operators try to keep diseases from taking hold by
applying protective
fungicides to the young transplants. Frequent, thorough
inspections tell the grower if a
disease is present.

"I know no greenhouse operator in Georgia would
knowingly sell diseased
transplants," Gay said. "Some of these diseases are
100 percent
destructive."

Commercial farmers and home gardeners do have a way to know
if their transplants are
disease-free. Just look for a label that indicates the
transplants are certified by the
Department of Agriculture as disease-free.

But Gay said transplants aren’t required to be certified.

"Farmers and gardeners usually rely heavily on cultural
control of viruses, fungi
or bacteria, no matter what their transplant source," he
said.

Even certified disease-free transplants could be infected by
pathogens carried on the
wind just after planting.

Gay cautions growers to use disease-control practices from
the first day they
transplant seedlings.

The county Extension office has more information about
controlling diseases in
transplanted crops.

"In this instance, prevention is not only much more
effective than control,"
Gay said, "it’s much less expensive, especially when
growers consider that the entire
crop could be destroyed by these pathogens."