Among primary clients are county agents, farmers,
nurserymen, greenhouse and sod farm operators, golf course and ground maintenance
personnel, arborists, and home gardeners.
Researchers at UT hope to release an anthracnose-resistant
dogwood cultivar within the next 12 months.
"Some turf diseases can wipe out a green
within a 24-hour period.
Many golf course superintendents bring samples
in to the center or ship them overnight. "
Citizens who are experiencing insect and plant
pest problems are urged to contact their county Extension office, which
has a supply of mailing materials.
|
The Doctor Is In
Scientists at UT diagostic center
answer your questions about insect pests and plant diseases.
by Sharon Littlepage
When it rains, it pours.
And if you're a farmer or home gardener, too much rain can be almost
as bad as not enough, often resulting in a banner year for plant diseases
and insect pests that can destroy even the most promising crop.
In 1996, for example, precipitation was greater than normal in the Mid-South
region, where 75 inches was recorded-just one inch shy of what is classified
as rain-forest levels.
Excess rainfall can lead to problems. Diseases such as damping off, blue
mold, bacterial leaf spot, anthracnose, and root rot are more prevalent
during cool, wet weather. Dogwood trees in particular have recently experienced
the wrath of powdery mildew, a fungal disease that can weaken the health
of some trees. Although most healthy trees can get over it without special
treatment, those already stressed don't always survive.
At UT's Plant and Pest Diagnostic Center, located at Ellington Agricultural
Center in Nashville and the only facility of its kind in the state, approximately
100 cases of powdery mildew were diagnosed by midsummer on dogwood trees
and other plants like lilac, wheat, and tomatoes.
Viral diseases such as tomato spotted wilt (TSWV) and impatiens necrotic
spot (INSV) can affect over 350 plant species and have been found all across
Tennessee and the eastern United States. These diseases can be prevented,
says plant pathologist Dr. Alan Windham, but there is no treatment for a
plant once it's been infected. "INSV will rapidly spread from one plant
to another in a greenhouse by thrips [a tiny sucking insect]," he stated.
"Within a week after it's been spotted, it has the potential to kill
all the plants, so it is a very potent disease.
"Sometimes there is only a small window of opportunity to treat
a particular problem like this," says Windham. "If that opportunity
is missed, about the only thing we can do is tell growers how to prepare
for next season."
Root rot was pervasive statewide on crops as diverse as tobacco, tomato,
bean, azalea, rhododendron, and Fraser fir, says Windham. It is a disease
that fools many gardeners because the symptoms look like those of a plant
not getting enough water. "When roots rot, they can't pick up water,
so leaves turn yellow and plants wilt," he explained.
Good drainage is the best way to avoid it, although there are products
available that can be used to treat the soil.
Nor have some flower varieties been spared Mother Nature's excess precipitation.
Periwinkles and petunias, for example, are actually tropical plants that
need tropical conditions. Those set out in early spring, when the weather
was cool and wet, frequently rotted and died.
Dogwood anthracnose, fungal leafspot diseases, canker diseases, root
rot, and blue mold are only a few of the diseases that are diagnosed at
the center, which each year receives some 4,000 plant and insect specimens
for examination and evaluation.
As if battling powdery mildew wasn't enough, the popular dogwood has
been fighting its deadly nemesis, anthracnose, for about a decade. The center
was one of the first to identify the fungus 10 years ago when it was found,
mostly attacking trees growing in shade at higher elevations. Alan Windham's
brother, Dr. Mark Windham of the UT Agricultural Experiment Station, has
led UT's anthracnose research efforts, so the two are working closely on
this tenacious problem.
Although it grows naturally in the wild, flowering dogwood is also a
major ornamental nursery crop in Tennessee, with dogwood sales accounting
for 10 percent of total nursery sales. Approximately 75 percent of all dogwoods
sold in the United States start in Tennessee as seedlings, rooted cuttings,
or grafted plants, says Dr. Mary Lewnes Albrecht, head of the Department
of Ornamental Horticulture and Landscape Design.
To combat the anthracnose problem, researchers at UT hope to release
an anthracnose-resistant dogwood cultivar within the next 12 months. "Producers
and landscape managers will be able to reduce their use of fungicides to
protect dogwoods from this disease, thus improving the profit margin for
both producers and landscape managers while reducing risks to the applicators
and the environment," says Albrecht.
"It will probably take about five years to gather the results after
the anthracnose-resistant trees have been placed in various trial gardens,
arboretums, and nurseries to determine if they're truly resistant,"
says Windham.
Even though dogwood anthracnose will eventually be brought under control
in commercial nursery operations and the center will likely see a decline
in those cases, there is never a dearth of other plant diseases and insect
pests to diagnose.
Among insects, mites, and spiders that have been especially troublesome
during the past couple of years are thrips, various scale insects, azalea
lacebugs, saw flies, Japanese beetles, spruce spider mites, flatheaded borers,
Asian ambrosia beetles, beet army worms, and the multicolored Asian lady
beetles.
Multicolored Asian lady beetles have been especially plentiful in recent
years, much to the annoyance of many homeowners. "These insects were
introduced to control aphids on pecan trees in the Southeast in 1978,"
Windham explained. "They have become such successful predators of aphids
on many plants that their numbers have exploded." In the fall, he said,
they aggregate on the exterior walls of buildings before moving inside for
the winter.
The number of spider identifications has increased because of public
awareness of the dangers of brown recluse spiders after a two-year-old boy
was killed by a bite from one in Rutherford County in July, Windham pointed
out.
The center, which is operated by the UT Agricultural Extension Service,
employs six Extension specialists on-site, although other scientists are
available on the UT agriculture campus in Knoxville and at the West Tennessee
Agricultural Experiment Station in Jackson to assist in difficult diagnoses.
The staff includes plant pathologist Dr. Steven Bost, entomologists Dr.
Frank Hale and Dr. Don Sudbrink, plant taxonomist Wendy Anderson, diagnostician
Tom Stebbins, and Windham, coordinator of the group.
In addition to providing plant problem diagnosis and insect and weed
identification, the center also offers fescue endophyte testing and nematode
analysis. Other tests are conducted on a seasonal basis, such as virus testing.
Among primary clients are county agents, farmers, nurserymen, greenhouse
and sod farm operators, golf course and ground maintenance personnel, arborists,
and home gardeners.
Providing diagnoses is not the only function the center performs; prescribing
management strategies is available as well. "What we do is comparable
to what a physician in general practice does," says Windham. "We
diagnose and then prescribe treatment."
Sometimes people don't even know their plants and trees are diseased.
"They know the plants don't look good and think that perhaps they've
applied too much fertilizer or pesticide," Windham said. In a recent
situation in Sumner County, for example, a greenhouse operator discarded
5,000 hanging baskets of diseased impatiens. "The grower didn't get
it identified," Windham related. "The next year he saw the same
problem and brought us a sample. Within four hours, we were able to confirm
that it was impatiens necrotic spot virus." As a result, the grower
wound up destroying only 1,000 pots that year. "If he had not brought
a sample in for identification and initiated the management strategies we
recommended, he probably would have lost all his hanging baskets again."
Windham also works with a number of golf courses, where one bent-grass
green might cost $30,000 to construct. Not surprisingly, he noted, the golf
course superintendent's job is on the line every day. "Some turf diseases
can wipe out a green within a 24-hour period." Many golf course superintendents
bring samples in to the center or ship them overnight. "I look at the
samples and either call or fax the diagnosis and management strategy,"
he stated.
Whenever possible, the staff will recommend IPM (Integrated Pest Management)
strategies. "Although chemicals are still important and we tend to
recommend them as a short-term strategy, we are primarily looking at long-term
changes that can be made to minimize the problem. For example, can you grow
a resistant host? Can you rotate crops? What cultural practices can you
use to prevent the problem? Those are some things we consider."
To aid in making speedy analyses, the staff archive insect and plant
disease specimens, which are also used at educational seminars and workshops
for growers and by Extension agents in lieu of slides, which don't make
quite the same impact. "People like the hands-on approach-things they
can pick up and observe and see what it's really like in the field."
Also included in the state-of-the-art facility are laboratories for diagnosing
nematodes (basic and soybean cyst nematodes) and fescue endophyte samples.
The latter, which leads to costly "summer syndrome" among cattle
and horses in Tennessee, was instrumental in getting the center off the
ground 10 years ago, replacing a much smaller service that existed on the
agriculture campus in Knoxville. A greenhouse at the center allows scientists
to observe symptom progression and treatment of diseased plants.
Costs for handling samples range from $5 for a basic nematode soil sample
to $20 for a seed grow-out test (in-state). There is no charge for visual
diagnosis or identification of weeds, diseases, and insect samples. Plant
and pest samples requiring incubation, rearing, isolation, culturing, virus
tests, serological tests, host inoculation, extensive keying for identification
and/or other recognized laboratory and greenhouse procedures require from
one to three weeks, and there is a $10 charge ($20 out-of-state).
What about the rare specimen that the staff can't identify? "We
can send it to a private lab out-of-state or to diagnostic labs at other
universities and agencies with whom we network," says Windham.
Cyberspace is even being used to track these insect and plant culprits
through the use of maps on web sites. "Using this technology, we contribute
information to electronic bulletin boards that track or predict when a certain
fungus or insect will reach this region of the country. Even producers have
easy access to the information through the internet.
"Because we're off-campus and don't have ready access to a library,
the internet is also an invaluable tool for learning about new insect or
disease problems or management strategies," he added.
Citizens who are experiencing insect and plant pest problems are urged
to contact their county Extension office, which has a supply of mailing
materials (specimen forms F-654, padded envelopes, address labels, insect
vials, and mailing tubes).
"If it's a plant, we always advise clients to send in the part of
the plant that's affected." Windham noted. "If a plant has root
rot but the client sent in only leaves, we would have to request another
sample."
For questions about sampling or test results, contact the Plant and Pest
 Diagnostic Center at (615) 832-6802. |