Aphid Alert 2002, No. 4, July 26

Aphid Situation in Week Ending July 26

Flight activity of the bird cherry-oat aphid, Rhopalosiphum padi, increased sharply during the sampling week ending 26 July. Our data suggests that 2002 will be a year of heavy bird cherry-oat aphid pressure. Our research implicates bird cherry cherry oat aphid and green peach aphid as the two most important vectors of PVY in our region. The large population pressure of this species early is not a good omen. As the cereals ripen, bird cherry-oat aphid flight activity increases. The first green peach aphid capture of the year occurred at Grand Forks. Green peach aphid arrived in sizable numbers in southern Minnesota early in the year, but few can be found on potatoes in the Northern Great Plains. Cooler temperatures during the past week may favor green peach aphid increase.

Weather Conditions and Late Blight

Cooler weather and high relative humidity prevailed over much of our region this past week. Such conditions are highly favorable for the development of late blight. To date, no potato late blight has been reported in Minnesota, North Dakota or Manitoba. Wisconsin has not been so fortunate. It is vitally important to maintain regular fungicidal protection of the crop because these materials, while effective protectants, can not arrest infection, should it occur. New growth needs to be protected and rain may wash fungicide from the foliage.

Potato late blight status reports

Subscriber Alert

This is the fourth 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 July 26

table showing Minnesota aphid capture data for the week ending July 26, 2002

North Dakota locations: mean aphid captures per trap during the week ending July 26

table showing North Dakota aphid capture data for the week ending July 26, 2002

Manitoba locations: mean aphid captures per trap during week ending July 26 (see Manitoba Agriculture and Food Website)

table showing Manitoba aphid capture data for the week ending July 26, 2002

Wisconsin, South Dakota and Nebraska locations: mean aphid captures per trap during the week ending July 26

table showing Wisconsin, South Dakota, and Nebraska aphid capture data for the week ending July 26, 2002

Figure: Trap locations in the Aphid Alert network in 2002

illustrated map of the upper midwest showing 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.

graph showing green peach aphid trap captures for 1992-1994 and 1998-2001, plus the week ending July 26, 2002

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.

graph showing bird cherry-oat aphid trap captures for 1992-1994 and 1998-2001, plus the week ending July 26, 2002