| Aphid
captures, week ending
July 27.
The first capture of a winged
green peach aphid occurred this week at Baker, MN. In 1999 and 2000, we
started catching winged green peach aphids in mid-June. Indications
are that green peach aphid numbers will remain low in 2001 throughout the
northern Great Plains. Green peach aphid do not survive outdoors in this
region, even as eggs. Each summer, populations are restablished by
founders arriving from southern locations where overwintering
occurs. This year, there have been relatively 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 have found green peach aphid on canola and
other brassicas, but numbers are low compared to the past three
years. In some urban locations, e.g., St. Paul and Duluth, we have
found green peach aphid to be abundant in gardens suggesting introduction
with transplants from glasshouses or shipped from other locations.
At Rosemount, MN, a heavy infestation of green peach aphid has
developed in experimental plots of canola treated with aldicarb (Temik).
This outbreak suggests that this population may be resistant to aldicarb,
or that the drought conditions prevailing at Rosemount have hampered
uptake of the insecticide. During the past two weeks, green peach aphid nymphs have
been detected on potatoes at several locations in the Red River
Valley. Presumably, they are present in all potato fields, but
colonies appear to be only recently established. Infestations
seldom extend more than a few rows into the field. Spraying the
outside rows (e.g., 20 rows or a single pass of an airplane) of seed
potato fields with methamidophos (Monitor), pymetrozine (Fulfill),
imidacloprid (Provado or Leverage), or thiamethoxam (Actara) should be
very effective at this time.
Aphid flight
activity of other aphid species increased considerably over the previous week, but continued to be
less than on the same date last
year. Most abundant were aphids associated with corn and small grain
cereals. Most common were bird-cherry oat aphid, Rhopalosiphum
padi, and corn leaf aphid, Rhopalosiphum maidis. Small
grains are starting to ripen across northern Minnesota and North Dakota,
so we expect flight activity of species associated with these crops to
increase sharply over the next 2-3 weeks. Cereal aphids are
potential vectors of PVY. Foliar insecticides are seldom effective
in preventing the spread of PVY or other non-persistently transmitted
potato viruses. But minerals oils can disrupt the acquisition and
transmission of non-persistently transmitted viruses such as PVY and
provide at least partial protection. In experiments we conducted in 2000,
spread of PVY was reduced 40% by weekly application of 2% mineral oil, Aphoil
(sold by
Agsco). We did not observe phytotoxicity even when Aphoil was applied as a
4% suspension, but caution should be excised when using higher rates
or when mixing with other pesticides.
Soybean aphid, Aphis glycines, was
found this week in the Baker, MN suction trap. The nearest known
field infestation of soybean aphid is at St. Paul, MN, 200 miles to the
southeast. Many soybean fields in south central and southeastern
Minnesota are heavily infested with soybean aphid. Often nearly
every terminal is infested, some with hundreds of aphids, and most
developing into winged morphs.
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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LATE BLIGHT ALERT! LATE BLIGHT ALERT!
Roger Jones, Dept. Plant Pathology, Univ. Minnesota
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Minnesota:
No late blight has been reported in North Dakota or Minnesota yet. Growers
can be complimented on keeping up on their spray schedules and
excellent job of cull pile disposal this year. As of today, July 27th
2001, a late blight alert warning has been issued for Freeborn County and
southern MN, including the towns of Waseca and Hollandale. ALL RED
RIVER VALLEY SITES, as well as all central lakes region sites have also been
alerted to favorable conditions for late blight. The following MN
locations have also attained late blight alert status:
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 44 (Linton) to 78 (Robinson), and for nonirrigated sites
from 47 (Cando, ND and Stephen, MN) to 60 (Humboldt, MN).
Call NDSU Potato Late Blight Hotline at 1-888-482-7286.
Wisconsin:
Cumulative severity values as of July 25 ranged from 40 at
Hancock to 102 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 Michigan.
Cumulative severity values are generally high and high rates and
short spray intervals are recommended (see Michigan web site for
recommendations for your area).
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