Aphid Alert 2002, No. 8, August 23
Aphid Situation in Week Ending August 23
Aphid flight activity was generally greater across the Northern Great Plains in the week ending August 23 than in the week previous. Green peach aphid captures were up almost 80% this week. Turnip aphid was the most abundant species representing about 80% of total aphid captures in the Minnesota and North Dakota traps. The principal source of both these aphids appears to be canola. With the maturing and harvest of canola we expect flight activity of these species to decline over the next week or two. Aphids associated with small grains have been abundant this year. Captures of bird cherry-oat aphid have been higher in 2002 than in any previous year of operation of the Aphid Alert network. Greenbug, another cereal aphid, also has been much more abundant in 2002. Both bird cherry-oat aphid and greenbug are efficient vectors of PVY. Sunflower aphid and thistle aphid have been abundant at some locations, but neither species is thought to be an important vector of potato viruses. State seed potato inspectors in Minnesota and North Dakota have seen little PLRV in their field inspections in 2002, but much PVY. Going into 2002, we probably had little PLRV inoculum but considerable PVY inoculum planted. There was almost no green peach aphid pressure in 2001 and few seed potato lots were rejected for PLRV. In contrast, PVY vectors were of moderate to moderately-high abundance in 2001 and because of the presence of ample inoculum in the seed planted, PVY was epidemic. Many area potato fields have been damaged by surface flooding in 2002. This creates sparse stands and often within field crop margins, both of which tend to attract winged aphids to land. This situation is likely to lead to increased virus spread. We anticipate that PLRV infection will not be a major problem in the 2002 seed crop because of the low level of inoculum and only moderate green peach aphid pressure. PVY is likely to again be epidemic in 2002, as in each of the previous 4 years. Growers are reminded that insecticidal sprays are seldom effective in preventing PVY spread. On the other hand, we achieved almost 60% reduction of PVY spread with weekly application of crop oil.
Weather Conditions and Late Blight
No late blight has been reported in either Minnesota or North Dakota in 2002. However, late blight was found last week in the Carberry area of Manitoba. Conditions for late blight development in the Northern Great Plains currently range from highly favorable in much of Manitoba where there has been recent rainfall to unfavorable in much of North Dakota. As the days shorten and temperatures cool there is increasing probability of heavy dews which can favor late blight development. Also, weather conditions can change quickly so it always good insurance for potato growers to maintain their regular fungicidal spray schedule until the vines are dead.
Potato late blight status reports
This is the eighth issue of Aphid Alert 2002. This newsletter is intended to alert seed potato producers in the Northern Great Plains to flight activity by aphid species that are 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 is updated as additional data becomes available. To become an e-mail subscriber, send us an e-mail message with the word "subscribe" in subject line. If you have no interest in receiving this newsletter by e-mail, please reply with the word "unsubscribe" in the subject line. Some e-mail subscribers may not wish to receive messages containing graphics. If so, reply with the the words "no graphics" in the subject line.
Minnesota locations: mean aphid captures per trap during the week ending August 23
North Dakota locations: mean aphid captures per trap during the week ending August 23
Manitoba locations: mean aphid captures per trap during week ending August 23 (see Manitoba Agriculture and Food Website). No data were available for Glenboro because the suction trap was knocked over and the pan traps were washed out by heavy rain.
Wisconsin, South Dakota and Nebraska locations: mean aphid captures per trap during the week ending August 23
Figure: Trap locations in the Aphid Alert network in 2002
Figure: Cumulative captures of green peach aphid (per trap), 1992-1994, and 1998-2001. Three distinctly different seasonal patterns of green peach aphid abundance have been observed. In 1998 and 1999 green peach aphid were abundant with total captures approximately an order of magnitude greater (10X) than that of 1992, 1993 and 1994, and two orders of magnitude greater (100X) than that of 1993 and 2001. For the Minnesota and North Dakota seed potato industry, low green peach aphid pressure in 1994 coincided with the end of a multi-year PVY epidemic and the low green peach aphid pressure of 2001 coincided with the end of a multi-year epidemic of PLRV. During the week ending August 23, green peach aphid flight activity increased 80% over the previous week, but overall 2002 has been a year of only moderate green peach aphid pressure.
Figure: Cumulative captures of bird cherry-oat aphid (per trap), 1992-1994, and 1998-2001. This aphid comes off wheat and other cereals. The species is typically abundant in the Northern Great Plains. In our area, green peach aphid and bird cherry-oat aphid appear to be the two most important vectors of PVY. Lowest abundance of bird cherry-oat aphid during the years the Aphid Alert network has operated was in 1994, which, coupled with low green peach aphid pressure, coincided with the end of a multi-year epidemic of PVY. Bird cherry-oat aphid flight activity has been higher in 2002 than in previous years of the Aphid Alert network.
Figure: Cumulative captures of bird cherry-oat aphid and green peach aphid (per trap), 1992-1994, and 1998-2001. These two aphids have been implicated as the primary vectors of PVY in the Northern Great Plains (see Aphid Alert 2002, no. 2). Other potential vectors of PVY, e.g., greenbug and turnip aphid are also abundant this year.
Discovery of Potato Mop Top Virus leads Canada to impose import restrictions on U.S. potatoes
Potato Mop Top Virus (PMTV) is a virus that can cause spraing-like symptoms in tubers and yellow blotches on leaves. PTMV is vectored by the Powdery Scab pathogen. After Maine reported discovery of PMTV in a research field in the state, the disease was also found in a commercial storage. When the USDA Animal Plant Health Inspection Service (APHIS) communicated this information to the Canadian Food Inspection Agency (CFIA), they were informed that CFIA has been testing potatoes imported from the U.S. for the last 18 months. Potato samples from 9 states, i.e., ME, FL, NC, VA, OR, WA, MD, CA, and ID, were positive for PMTV. CFIA has sent a formal notice to APHIS indicating changes in import requirements for US potatoes into Canada. Discussions between APHIS and CFIA are ongoing.
More information of this story can be found at these URL's: http://www.spudman.com/pages/news02_08/news_canada_ban.html and http://cbc.ca/stories/2002/08/19/potatoes020819.
In susceptible cultivars, PMTV infection can cause tubers to develop concentric arcs of necrotic and circles of necrotic tissue (spraing symptoms).