CattleNetwork.com, KS
07-20-07
Potentially Damaging Soybean Aphids Again Found In Kansas
MANHATTAN, Kan. - Soybean aphids, which have the potential to wreak havoc
in soybean fields, have again arrived in Kansas.
This year´s soybean aphids were first discovered July 12 in a research plot by
Kansas State University plant pathology leader Doug Jardine and Lyon County
agricultural Extension agent Brian Rees.
The plot is a sentinel plot, used to monitor the possible occurrence of soybean
rust and soybean aphids. Both are potential threats to the state´s soybean crop,
according to Extension entomologist Jeff Whitworth.
Five days after Jardine and Rees´ discovery, soybean aphids were found in Riley
Co.
"These are the first 2007 reports of soybean aphids in Kansas. They´re
somewhat earlier than in past years, although approximately in the same time
frame as seen in 2005," Whitworth said. "But, populations that year never really
became troublesome."
The soybean aphid, Aphis glycines, was first detected in the United States in
2000 and first detected in Kansas in 2002.
"We have had soybean aphids every year since, but only in 2004 did they
become a problem of economic consequence, requiring some fields to be treated
with insecticides," Whitworth said. "In fact, only one county had verified soybean
aphid populations in 2006."
Entomologists Carol Pilcher, Marlin E. Rice and Todd Vagts of Iowa State
University released an ISU research-based Extension publication in 2005 that
stated:
"This pest has the potential to cause approximately 3 million acres to be sprayed
and to cause losses of more than 55 million bushels, meaning an economic
impact of more than one-quarter billion dollars in an outbreak year. These results
reinforce the need for scouting to accurately determine the soybean aphid
populations in your fields and emphasize the use of current threshold
recommendations to justify the costs of applying insecticides. These steps are
key to saving dollars in the management of soybean aphids."
More about the ISU study is on the Web at:
http://www.ipm.iastate.edu/ipm/icm/node/53.
Soybean aphid populations seem to be sensitive to hot temperatures -specifically temperatures over 95 degrees, K-State´s Whitworth said. High
summer temperatures may not actually kill the aphids, but it does seem to
drastically reduce their ability to reproduce, he said. And, if they are not rapidly
reproducing, this gives some of their
natural enemies, such as predators and parasites, the opportunity to help
regulate the aphid populations.
Aphid populations can increase very quickly because they reproduce
parthenogenically, he said. This means they don´t have to mate and lay eggs.
Each aphid is a female and thus produces females that produce females and so
on, without any lag time of looking for mates and waiting for eggs to hatch. They
are born and start feeding and producing young immediately.
Soybean aphids are the only North American aphids to colonize and develop
large numbers on soybeans, Whitworth added. They´re relatively small, lightgreen aphids with distinctive black cornicles or "tail pipes" at the tip of their
abdomen. Infestations usually start at the outer canopy on newer soybean
leaves. Aphids can be throughout the canopy, but well-established populations
most often will be on the undersides of leaves and on stems and developing
pods.
"This aphid can transmit many viral diseases, but it also can stress plants and
reduce yields by virtue of their feeding, which removes nutrients from the plant,"
the entomologist said.
Infested plants may have a distorted, yellow appearance and may become
covered with a slick, sticky substance called "honeydew" -- which itself often
becomes dark and sooty, due to molds living on the honeydew. Ants seem to be
attracted to this honeydew, so "if you see ants in your soybean canopy, that may
be an indicator of an aphid infestation," he said.
The aphid populations discovered in Kansas so far are small and widely
scattered, Whitworth said. However, this year´s soybean crop in general is a
little late in development, and that might make it more vulnerable to insect
damage.
In its July 16 weekly report on crop conditions, the Kansas Agricultural Statistics
Service said 38 percent of the soybeans statewide were blooming. This put the
crop well behind the 63 percent blooming at the same time last year and the 46
percent five-year average.
Soybeans in the late vegetative and early reproductive stages are probably the
most susceptible to aphid feeding, Whitworth said.
States with annual soybean aphid problems have set the economic thresholds for
applying controls at around 50 aphids per plant in pre-reproductive plants and
about 250 per plant in the R1 (beginning bloom) to R4 (full pod) stages. The
thresholds take into account a seven-day lag between scouting and treatment,
for time to make the arrangements to treat, he said.
Whitworth is encouraging producers who find a soybean aphid infestation to
report it to their county or district K-State Research and Extension office.
In addition, Extension offices have information about sampling, a new technique
called "speed scouting," treatment thresholds, and insecticides registered for use
against soybean aphids. More information also is available on the Kansas
Extension Web site:
http://www.entomology.ksu.edu/DesktopDefault.aspx?tabid=668.