Aphid Alert: Region-wide virus vector surveillance for
the Minnesota and North Dakota potato industry
Edward B. Radcliffe, radcl001@umn.edu
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Aphid
Alert 2001, No. 8, August 10
Published cooperatively by
the
Department of Entomology,
College of Agricultural, Food & Environmental
Sciences, University of Minnesota, the University of Minnesota Extension Service,
and the State Seed Potato Programs of
Minnesota and North Dakota
Project funding
provided by:
Minnesota State Legislature,
Rapid Agricultural Response Initiative &
United States Department of Agriculture,
Cooperative State Research, Education and Extension Service,
Integrated Pest Management Program, North Central Region
WWW address:http://ipmworld.umn.edu/alert.htm
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| Aphid
captures, week ending August 10.
We have completed our eighth week of aphid
trapping for 2001.
The past
week has been marked by continued extreme heat and violent storms across the
Red River Valley of the North. Several locations experienced straight
line winds of 100 miles per hour and very heavy rain. Many fields have been lost or damaged by standing water.
Green peach aphid, Myzus persicae, and turnip aphid, Lipaphis
erysimi, appear to have fared badly
under such adversity and now with canola harvested or senescing, this source
appears largely eliminated. For potato growers, late blight must now be their
first concern. If late blight infection occurs in the region, the risk
of spread would be very high.
Notes:
Locations for which data were not available when this page was
created will be updated as results are received.
One suction trap and two pan traps are operated at each
location, except at Crookston, Rosemount and Thief River Falls which have
more. Data are
reported as total aphid captures per three traps.
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Captures of green peach aphid per trap, 1992-1994,
1998-2000 (click on figure on left to view larger image).
Abundance of green peach aphid
has differed greatly from one year to the next. In the years
1992-1994 (green lines), captures of green peach aphid were
consistently low, in 1993 only 7 were captured all year. In 1998
and 1999 (red lines) , mean weekly captures were 6 times that of
1992-1994. In 2000 (yellow line), the mean weekly capture rate
was comparable to that of 1992 and 1994. Peak green peach aphid
flight activity occurs in early-mid August, about one week after peak
flight activity of other
potential PVY vectors.
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Comparison of captures of green
peach aphid per trap in 2000
and 2001.
Summer 2001
is becoming a repeat of 1993, a year with essentially no green peach
aphid flight activity. Recent heavy rains and hot
temperatures appear to have all but eliminated green peach aphids on
canola and removing that threat.
We do not anticipate that captures of green peach aphid will increase
appreciably over the next several weeks.
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Captures of PVY vectors other
than green peach aphid per trap, 1992-1994,
1998-2000 (click on figure on left to view larger image).
Abundance
of potential PVY vectors other than green peach aphid have differed
greatly from year to year. Total captures in 1998 were 20 times that
of 1993, and 2-3.5 times that of other years. Species
predominance differed among the years but there were also differences
among locations. Combining data from all dates and trap locations, the
most abundant aphid in 1998 was the sunflower aphid complex Aphis
helianthi Monell, (70% of total captures). In 1999 the most
abundant species was the turnip aphid, Lipaphis erysimi (Kaltenbach)
(25% of total captures). In 2000 the corn leaf aphid, Rhopalosiphum
maidis (Fitch) comprised 35% of total trap captures.
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Comparison of captures of
potential PVY vectors (other than green peach aphid) per trap in 2000
and 2001.
Corn leaf aphid, Rhopalosiphum maidis, continues
to be the most abundant aphid in trap captures. Some locations
have high densities. We are capturing only small numbers of
bird-cherry oat aphid, Rhopalosiphum padi, English grain aphid,
Sitobion avenae, and
greenbug, Schizaphis graminum We have captured very
few turnip aphids, Lipaphis erysimi.
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Insecticide
Trial for Soybean Aphid,
Aphis glycines Matsumura, 2 August 2001
David Ragsdale, Ken
Ostlie and Erin Hodgson
University of Minnesota
Click
on image to view larger file.
Caution: This information applies to soybean
aphid and should not be used to select insecticides for aphid control on
potato. To see our most recent insecticide trial on green peach aphid
see Aphid Alert 2000, no. 7
For more information on soybean aphid in
Minnesota view the Minnesota
Pest Report, August 10.
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Results: Most
registered products tested gave satisfactory control of the
soybean aphid. Two compounds, Pounce and Dimethoate,
significantly provided only 85-90% control of the soybean
aphid. In general, 95% control or above is needed to prevent
resurgence of the aphid population following treatment. As
with all aphid control, better results are achieved with high
pressure and high volume. Here we used 42 psi and 30 gallons
of spray solution per acre. Our plots also lacked a
closed soybean canopy allowing for good penetration of
insecticide into the lower canopy. All products gave
equivalent control of soybean aphids whether in the top or
lower canopy.
We tested all
products at the highest labeled rate. It is our opinion that
those products that gave near 100% control could be used at
the lowest labeled rate and still achieve satisfactory control
(>95%). The key to good aphid control is less dependant
upon rate than on using adequate spray volume (at least 20
gallons per acre) and high pressure (40-80 psi).
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LATE BLIGHT ALERT! LATE BLIGHT ALERT!
Roger Jones, Dept. Plant Pathology, Univ. Minnesota
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Minnesota:
Temperatures across Minnesota have been extremely hot for the past couple of
weeks. The region has been recently swept by violent storms and much
rain. Many fields have standing water and the air is very humid.
Nearly all regions of Minnesota have now experienced ideal conditions for
the spread of late blight. No late blight has been reported in
Minnesota, but please keep a close watch!! Scout your fields and
continue your spray program. Do not hesistate to contact Roger
Jones (1 888 335 8636) if you have concerns. The following MN
locations have attained late blight alert status: Alexandria and St. Cloud
(Aug. 2), Becker (July 30, Hollandale (July 28), Perham, Staples (July 20), Baudette, Crookston, Eldred, Felton, Karlstad,
Stephen, Williams (July 16 & 18), Brooten, Foxhome (July 9), Humboldt
(July 4), Warren (July 3), and Little Falls, Park Rapids (June 15).
North
Dakota:
Recommendations as of Aug. 8: Late blight
favorability values have become negative the past five days due
to the hot weather. Hot nights limit the sporulation and spread
of late blight, but do not kill it. It can remain viable in the
plant until cool wet weather reappears. The forecast calls for
cooling temperatures for the next few days, which will provide
conditions more favorable for late blight. We still do not have
late blight reported in our region, but growers should continue
to do the big three management practices: scout fields, monitor
the weather, and apply fungicides regularly. The weather
continues to be the dominant factor influencing potato
production, resulting in drown outs, hail damage, wind damage
and flooded fields. Remember to disc up damaged fields and apply
fungicide to abandoned fields.
Wisconsin: The
rains have resumed and pose a threat of additional spread of
late blight. IPM scouts are reporting additional fields with
symptoms of late blight. While the general scenario is a few
infected leaves here and there, the distribution of late blight
throughout central WI poses a concern. Long periods of high
relative humidity and leaf wetness could pose problems for
containment of late blight as we move into the last month of
maintaining foliage health. The area of late blight concern also
continues to expand with late blight as far south as Coloma and
north to the Antigo area. Fungicide spray programs should
continue on a 5-7 day interval until vine kill. For the most
part, control of late blight is excellent. This was achieved by
careful, but not excessive use of fungicides to maintain
protection of all foliage as we have moved through the growing
season. Severity values have increased substantially during the
past week, especially in northeastern WI. Growers should plan
their spray programs accordingly.
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Last modified: Tuesday, August 14, 2001
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