Syngenta Thrive - 2Q/2013 - 14

Modes of action
in South Carolina. “This is creating resistance issues that
are spreading rapidly.”
Another example is Cercospora leaf spot, a destructive
foliar disease in sugarbeets. It can become a major
challenge when growers rely too much on one treatment,
such as triphenyltin hydroxide (“tin”).
“Resistance is serious, because it substantially reduces a
grower’s ability to control crop diseases,” says Gary Secor,
Ph.D., a professor of plant pathology at North Dakota State
University in Fargo. The fungal diseases that create some of
the greatest resistance challenges typically produce an
abundance of spores, he adds.
Insects Take a Toll
Insects are also posing serious resistance challenges.
Corn rootworms already cost U.S. producers more than
$1 billion per year, but now the pests are adapting to
current control methods.
“This pest is evolving as fast as solutions are being
developed to control it,” says Craig Abell, a Syngenta crop
specialist based in Champaign, Ill.
There has been confirmed resistance of Western corn
rootworms to the Cry3Bb1 (YieldGard® Rootworm) protein.
Outside the Corn Belt, a serious threat involves the Asian
citrus psyllid, which invaded Florida more than a decade
ago and transmits one of the world’s most destructive citrus
diseases. “This pest has the potential to seriously impact
the U.S. citrus industry,” says Caydee Savinelli, Ph.D.,
Syngenta technical product lead for insecticides. Additional
spray applications to control this insect have raised potential
resistance issues, highlighting the importance of using

12 · thrive · 2Q/13

IPM strategies
different modes of action to extend the life of valuable crop
protection products.
Use Smart Strategies
When it comes to combating resistance issues, experience shows that relying on a single mode of action
is much less desirable than adopting a multipronged approach to combat diseases and pests,
says katherine Stevenson, Ph.D., a professor in the
Department of Plant Pathology at the University of
Georgia in Tifton. “When a new herbicide, insecticide
or fungicide first becomes available, it works great for
a few years, but then resistance starts developing
when the product is used exclusively.”
Stevenson has seen this pattern develop repeatedly
in watermelon production, when growers rely too heavily
on one fungicide to control gummy stem blight, which can
destroy 100 percent of the crop in a hot, wet year.
“most modern fungicides have a very site-specific mode
of action, meaning they have only one specific biochemical
target in the pathogen, rather than multiple targets,” she
says. “This inherently puts products with a single-site mode
of action at a higher risk for resistance.”
experts agree it’s time to take a proactive approach
to resistance management, which includes:
> Using multiple modes of action. It’s important to
incorporate different classes of chemistries during the
growing season. To control weeds in row crops, for
example, it’s important to apply residual herbicides
with effective modes of action for control of vulnerable
germinating weeds, says Brett miller, Syngenta technical

PhOTOS: (FROm leFT TO RIGhT) DeeRe & COmPANY, SYNGeNTA, ISTOCk



Syngenta Thrive - 2Q/2013

Table of Contents for the Digital Edition of Syngenta Thrive - 2Q/2013

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