Aphid Alert: a research/outreach program providing region-wide virus vector surveillance
to
the Northern Great Plains potato industry.
Aphid
Alert 2003, No. 9,
August 15
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:
the Northern Plains Potato Growers Association,
the Minnesota State Legislature,
Rapid Agricultural Response Initiative
&
the
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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Potato insect update for the Northern Great Plains, week ending
August 15 Aphid flight activity continued to be high across the Northern Great Plains during the past week. In Minnesota and North Dakota, the species most abundantly represented in trap captures were turnip aphid > corn leaf aphid > and sunflower aphid. Collectively, these 3 species represented almost 2/3 of total aphid captures. Each of these aphids is reported to be capable of transmitting PVY, but there is little evidence that they are important in PVY spread. In Manitoba, buckthorn aphid accounted for 80% of total aphid captures. Both buckthorn aphid and potato aphid have been common on potato in Minnesota and North Dakota this summer. Although neither is as efficient in virus transmission as green peach aphid, potato aphid and buckthorn aphid vector both PVY and PLRV. Green peach aphid numbers were up slightly from the previous week. Cumulative captures of green peach aphid have been relatively low in 2003 compared to some previous years, e.g., 1998 and 1999. However, a major green peach aphid colonization event occurred during the last week of July. That colonization event was the trigger for launching a planned large scale on-farm experiment to assess the efficacy of border application of insecticide as a means of slowing establishment of green peach aphid in potato. Pretreatment counts showed that green peach aphid numbers were approximately 15 times higher on plants within a spray swath width of field margins than in the interior. However, fields with drown outs, planting skips, or even gaps caused by roguing had greater within field colonization than fields having uniform stands. In this experiment, colonizing green peach aphids behaved as expected, and aerial application of a single swath of Monitor spray provided good aphid control. We will caution that the window for successful control using border treatments may be past. It can be expected that once colonization has occurred, the aphid population will build and become dispersed across the field. Some early seed potatoes have already been killed. Seed potato growers should vine kill as early as is economically realistic. State seed potato inspectors report seeing much current season mosaic this summer. Crop oils offer better protection against the spread of PVY than do insecticides. Also, we have seen some fields with considerable leafroll. With so much virus inoculum in the system and recent weeks of weather favorable for aphids, the risk of potato virus spread appears very high. While many growers have achieved excellent aphid control, we have seen more than a few potato fields with high populations of green peach aphid and potato aphid. Potato aphid numbers appear to be declining, but green peach aphid are increasing. Late summer flights of green peach aphid are of especial concern because these aphids are likely to have come from potato and to vector virus. Soybean aphid numbers are
increasing rapidly on soybeans in northwestern Minnesota.
Soybean is now a major crop in this region with more than 1.7
million acres. Indeed, Clay County, Minnesota, has more
acres of soybean than any other county in the U.S. We catch
few soybean aphids in our traps, even in southern Minnesota where
this summer several million acres have required spraying for this
pest. When populations are high, this aphid shows a
remarkable propensity to produce winged adults. The number
of winged aphids produced on a single soybean plant can be in the
hundreds. In laboratory research, we have found soybean
aphid to be a fairly efficient vector of PVY. The importance
of this aphid in transmission of potato virus has yet to be
determined, but we believe there is reason for concern. |
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Minnesota-North Dakota aphid data, week ending
Aug. 12 |
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Manitoba aphid data, week
ending Aug. 14 Additional information on the aphid situation in Manitoba can also be found at www.gov.mb.ca/agriculture/crops/insects/index.html, and the Manitoba Agriculture and Food potato hotline at 1-800-428-6866. |
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Late Blight Situation
Hot, dry weather continues to predominate across the Northern
Great Plains. The potato crop is in good to excellent
condition, but most nonirrigated potatoes
would benefit from rain. While the prevailing weather
conditions do not favor development of Potato Late Blight, the
closed canopy of a potato field provides a microenvironment with
high relative humidity. That has pushed Disease Severity
Values above threshold at nearly all locations. When rapid
increases in Disease Severity Values occur, this indicates that
environmental conditions were favorable for Late Blight
development. There will more hours daily of high humidity
as daylight become shorter and
mean temperatures diminish. This will favor the development of foliar
diseases. It will be increasingly important to maintain
the fungicide application regimes recommended for your area to
minimize risk of disease. Today, Manitoba reported new
instances of suspected Potato Late Blight from Carberry and
Winkler.
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Potato late blight status reports Minnesota North Dakota Wisconsin Manitoba |
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Subscriber
Alert This is the ninth issue of Aphid Alert for the 2003 growing season. This newsletter is intended to alert seed potato producers in the Northern Great Plains to flight activity by aphid species known to be potential vectors of potato viruses. We report results weekly on the WWW, by e-mail to subscribers, and by surface mail to all Minnesota and North Dakota seed potato growers. The hard copy and e-mail versions of Aphid Alert report aphid capture data available as of the date they are mailed. The WWW version will be updated as additional data becomes available. To become an e-mail subscriber to Aphid Alert 2003, send us an e-mail message with the word "subscribe" in subject line. Note that current subscribers need not resubscribe. If you have no interest in receiving this newsletter by e-mail, please reply with the word "unsubscribe" in the subject line. |
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Ted Radcliffe Last modified: Friday, August 14, 2003 © Regents of the University of Minnesota, 2003
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