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. 7, August 3
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 3.
We have completed our eighth week of aphid
trapping for 2001. We still can only report the capture of one lone
green peach aphid (last week at Baker). The same situation exists in
Scotland. The July 22 Scottish Aphid Bulletin reports "The summer goes
by but still the aphids in Scotland refuse to fly. " In view of
the low level of potato aphid activity, and the low level of activity of
other aphid species that vector non-persistent viruses, aphid monitoring in
Scotland was ended for 2001 as of July 31. In the northern U.S., the
2001 growing season has had few wind events
favorable for the long-distant transport of green peach aphids to the
northern Great Plains (see MinDex in
Aphid Alert no. 5). We are finding green peach aphid and turnip
aphid, Lipaphis erysimi, on canola and
other brassicas, but numbers are low compared to the past three
years. Corn leaf aphid, Rhopalosiphum maidis, has been the
most abundant aphid in our trap collections. The total of aphids other
than green peach aphid captured in 2001 is less than on the same date
in 2000. The species complex is different between the years with many
more corn leaf aphid and fewer turnip aphid in 2001. The
past week has seen very heavy rainfall throughout much of the Red River
Valley region of Minnesota and North Dakota. Many production fields
have been lost or damaged by standing water. Indeed, we have lost many of
our experimental plots. For potato growers, late blight must now be their
first concern. If late blight infection does occur in the region, the risk
of spread will 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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This year is shaping up to be a repeat of 1993, when there was essentially no green peach
aphid flight activity all summer. Still, we urge
caution. Much virus infected seed was planted this spring by
commercial growers. We have to assume that even with low vector
numbers the risk of virus spread to seed fields remains high.
Since July 23, we have observed a 5-fold increase in green peach
aphid numbers on canola. We expect green peach aphid flight activity
will pick up with the onset of canola harvest.
Thus, growers should scout their fields frequently (at least twice a
week), especially on field margins and corners, to detect colonization.
Remember that green peach aphid favors the underside of lower leaves
of the plant. Focus scouting on the lower third of the potato
plant. When green peach aphid densities reach the threshold of 3
wingless green peach aphids per 100 leaves insecticides should be
applied to prevent the spread of PLRV. However, the most effective
method to reduce spread of both PVY and PLRV spread is to kill the
vines as early as feasible. |
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Corn leaf aphid, Rhopalosiphum
maidis, was abundantly represented in trap captures at most
locations. Small grains are ripening across the northern Great Plains,
but apparently these crops supported few aphids this year. We
continue to catch only small numbers of bird-cherry oat aphid, Rhopalosiphum
padi, English grain aphid, Sitobion avenae,
and greenbug, Schizaphis
graminum Canola harvest should be underway
next week. With the maturing of canola, we anticipate increased
flight activity of turnip, Lipaphis erysimi and green
peach aphid. Soybean aphid, Aphis
glycines, continues to spread quickly across the state. In
southeastern Minnesota (from Minneapolis south and east) virtually
100% of the plants are heavily infested (100 or more aphids per
terminal). Plant injury is common. Insecticide trials
recently completed suggest that most organophosphate insecticides registered for use on soybean give
excellent control, but that pyrethroids do not perform well,
especially when it is hot.
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on image to view larger file.
Joseph Munyaneza, David W. Ragsdale,
Edward B. Radcliffe, and Andi Nasruddin
Department of Entomology, University of Minnesota (experiment reported in
Arthropod Pest Managment, 2001, ESA)
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A green peach aphid control experiment
was conducted at Rosemount, MN in 2000. NewLeaf Russet
Burbank’ potatoes were used to eliminate Colorado potato
beetle as a factor in the experiment. Starting June 22,
all plots received a weekly application of the fungicide Bravo
Zn to prevent late blight and weekly application of
Guthion 50WP to control potato leafhoppers and increase green
peach aphid densities.
Aphidicides were
applied 9 Aug using a tractor-mounted Brittonya boom
sprayer with 3 drop nozzles per row and delivering 33 gal/acre
at 45 psi. Sampling involved counting aphids on 35 mid-potato
plant leaves per plot. Plots were replicated 4 times per
treatment.
Monitor 4EC
provided excellent control within 2 d of treatment. High
rates of Actara 25WG and Provado 1.6F were effective 5 d after
treatment. Fourteen days after treatment, Actara 25WG, Fulfill
50WG, and Monitor 4EC were providing best aphid suppression.
To read more about Fulfill
insecticide and managing insecticide resistance in potato
aphids read the interesting article by Andy Evans of the
Scottish Agricultural College.
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LATE BLIGHT ALERT! LATE BLIGHT ALERT!
Roger Jones, Dept. Plant Pathology, Univ. Minnesota
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Minnesota:
Growers of the region must be commended for their vigilant late blight
control program since no late blight has been found in the Red River Valley
yet. Unfortunately, the torrential rainfall of 31 July (ranging from 1.5
inches in Nielsville, (MN) to over 6 inches in Baudette (MN) caused field
conditions that could delay this week’s scheduled fungicide applications
with a ground sprayer. Weather conditions are very favorable for late blight
infection. We strongly recommend you avoid any skip in the
late blight program and apply fungicides by air. Special attention should
be placed on low lying areas of fields where plants are under the most
stress and thus most susceptible to late blight infection. Disking these areas
under or treating them with vine kill chemicals could prevent
establishment of late blight in the field. The following MN
locations have attained late blight alert status:
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). The
weather has been favorable for late blight to spread. Please take the
appropriate precautions and scout your fields frequently.
North
Dakota:
Cumulative severity values as of July 25 for irrigated sites
ranged from 64 (Linton) to 104 (Robinson), and for nonirrigated sites
from 62 (Stephen, MN) to 950 (Warren, MN).
Call NDSU Potato Late Blight Hotline at 1-888-482-7286.
Wisconsin:
Cumulative severity values as of July 25 ranged from 44 at
Hancock to 107 at Plover. Late blight is currently confined to
an area of central WI that stretches from Coloma to Plover.
The extent of the area is a concern for all growers in this area
of the state. At this point in the season, no late blight
has been reported from northwest, northeast, southwest,
south-central or southeast WI. Growers continue to spray
production fields on 5-7 day intervals. Now that
weather conditions have returned to a more normal pattern with
periodic rainfall and somewhat cooler temperatures, we can
expect an increase in disease pressure. See Wisconsin web site for recommendations for your
area.
Michigan:
Late Blight has been found in Montcalm
County at the following locations (and approximate number of
infected fields) as of 7/30/01: Cedar Lake(2), Vestaburg(3),
Lakeview Area(8), Edmore(3). If late blight has been found
within 2-5 mi of your fields, apply systemic fungicides at full
recommended application rate or protectant fungicide plus
Supertin at 3 - 3.75 oz/acre -- minimum 7 day application
interval. If late blight has been found within 1 mi, shorten
interval between applications to maximum of 5 days. For more
detailed information about your location visit Michigan State
University, Late Blight Lab web site.
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Last modified: Friday, August 3, 2001
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