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August 17, 2007
Michigan is still the No. 1 state
in pickling cucumber production, but a readily spread disease
infecting up to 50 percent of the state’s cucumber acreage
threatens to put an end to that claim and jeopardizes the future
of several other important vegetable crops.
The culprit is Phytophthora capsici, a funguslike organism that
infects plant roots, fruits and foliage and causes a blight, or
rot, to appear on the infected parts of plants in several
families of crops: the cucurbits (cucumber, pumpkin, gourd,
watermelon, cantaloupe, and summer and winter squash) and
solanaceous (tomato, eggplant and pepper) families, as well as
lima, wax and snap beans. Infection reduces yields and can kill
plants outright within a few days. In 2006, Michigan growers
produced $132 million worth of these vegetables on more than
83,000 acres. When weather conditions are favorable for
Phytophthora (warm with rain), crop losses can reach 25 percent
or higher.
“The economic losses from Phytophthora can be devastating,” says
Mary Hausbeck, Michigan State
University (MSU) professor of plant pathology and lead
researcher on the Phytophthora project. “When a farm in southern
Michigan was unable to harvest 300 acres of diseased pickling
cucumbers because of Phytophthora, an estimated $300,000 was
lost. This was in addition to a $40,000 loss on approximately
100 acres of processing tomatoes.”
Because of the economic importance of these vegetable
commodities to Michigan and the threat that the disease presents
to the state’s growers, plant pathology researchers at MSU are
seeking to identify strategies for understanding and controlling
Phytophthora, which can persist in soils in the absence of a
host for more than 10 years. They cite two findings as key.
The first discovery dates back to 1999, when they learned that
Phytophthora had become highly resistant to the primary
fungicide that growers had been using to control it.
“This meant that growers were spending a lot of money on a
product that could not help them,” Hausbeck says. “This finding
caused the pickle industry to shift to using alternative
products that did work and helped Michigan acquire a Section 18
registration that some other states did not have.”
The second key finding, from research conducted between 2002 and
2005, is that some of the water sources that farmers were using
to irrigate their crops were contaminated with the Phytophthora
pathogen. In standing water, Phytophthora produces swimming
spores that can be spread through moving water. The pathogen can
survive and cause infection for 8 to 10 hours, long enough to be
spread over many acres through irrigation.
“The significance of this finding is huge because large parcels
of farmland can become infected with Phytophthora after just two
waterings with contaminated water,” Hausbeck says. “That land is
infected forever, so growing vegetables there ever again is
risky.”
Hausbeck says that, prior to this project, little was known
about how Phytophthora spread so quickly and why it was a
particular problem in fields where vegetables had never been
grown in the past. For example, nearly 4,000 acres of vegetable
crops were affected when P. capsici was discovered in the
Pentwater River, a major waterway used as an irrigation source.
In response to this finding, six wells were drilled to provide
supplies of clean irrigation water for these farms.
“Discovering that this pathogen can be spread through irrigation
water has been the hardest one for growers to resolve,” she
says. “Irrigating with well water is safe, but using surface
water from ponds, rivers, creeks or ditches is not, especially
if there is a history of Phytophthora in the region.
Phytophthora is not visible to the naked eye, and the
cleanest-appearing ponds can be contaminated with it, so it can
be difficult for growers to understand why they must shoulder
the expense of digging a well.”
And what messages should growers take to heart?
“If irrigation is necessary, refrain from using surface water
sources,” Hausbeck says. “Instead, use drip irrigation from well
water or ponds fed by well water to reduce the risk of spreading
Phytophthora.”
It’s also recommended that growers irrigate conservatively and
limit irrigation close to harvest time.
MSU researchers are continuing to evaluate new products with
potential for managing Phytophthora. Monitoring of irrigation
water sources for Phytophthora continues, and scientists are
initiating research to determine the role that water temperature
plays in the pathogen’s survival. Project GREEEN, Michigan’s
plant agriculture initiative at MSU, continues to provide
funding in support of this work.
“Project GREEEN has been there since the beginning, and it was
key to helping us secure the funds necessary to acquire the
technical expertise needed to identify the fungicide resistance
problem,” Hausbeck says. “Phytophthora research and the grower
recommendations resulting from it would not have been possible
without funding from Project GREEEN.”
Founded in 1997, Project GREEEN (Generating Research and
Extension to meet Environmental and Economic Needs) is a
cooperative effort between plant-based commodities and
businesses together with the Michigan Agricultural Experiment
Station, MSU Extension and the Michigan Department of
Agriculture to advance Michigan’s economy through its
plant-based agriculture. Its mission is to develop research and
educational programs in response to industry needs, ensure and
improve food safety, and protect and preserve the quality of the
environment.
To learn more about the state’s plant agriculture initiative at
MSU, visit
www.greeen.msu.edu. |
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