Aphid Alert 2002, No. 3, July 19
Aphid Situation in Week Ending July 19
Aphid flight activity increased this week. Bird cherry-oat aphid captures doubled during the sampling week ending on 19th of July with numbers 2-fold higher than in the same week in 2001. The increase in winged aphids corresponds with the buildup of aphids in small grains fields across the region. No winged green peach aphids have been captured in the traps and apterae are rare in potato fields. We have one report of green peach aphid detection on potato from Tappen, North Dakota. Green peach aphids are found on canola but their numbers are low for this time of the year. The high temperatures observed this week in the region approached the upper developmental threshold of green peach aphid. Above 90 °F (32 C), reproduction diminishes and mortality rapidly increases in green peach aphid populations. However, growers should be cautious in interpreting this observation because aphids have a very high reproductive potential. A single green peach aphid can give birth to ~80 nymphs during its reproductive life of approximately 3 weeks. Under favorable conditions these newly born nymphs can reach reproductive maturity within 7 days. Thus, when conditions become favorable aphid populations can increase explosively. Vigilant monitoring of seed potato fields is strongly recommended.
Weather Conditions and Late Blight
During the past week conditions were generally favorable for the development of late blight over much of North Dakota and Minnesota. All irrigated and non-irrigated production areas have surpassed or are nearing the threshold severity value of 15. Scattered thunderstorms are probable throughout the region for the next two days making it imperative that potato growers adhere to rigid spray schedules. Thunderstorms promote field to field spread of late blight. Potatoes are now growing rapidly so it is important to protect new foliage with fungicide. To this point, no late blight has been reported in North Dakota or Minnesota.
Potato late blight status reports
This is the third 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 19
North Dakota locations: mean aphid captures per trap during the week ending July 19
Manitoba locations: mean aphid captures per trap during week ending July 19 (see Manitoba Agriculture and Food Website)
Wisconsin, South Dakota and Nebraska locations: mean aphid captures per trap during the week ending July 19
Figure: Trap locations in the Aphid Alert network in 2002
Aphid Alert expands to Montana
Figure: Corrie Enander of Westby, Montana, shown here with Aphid Alert's Robert Suranyi, after loading an 8 ft suction trap on the top of Corrie's Ford Taurus. Remarkably, Corrie and the trap reached Montana safely despite encountering a storm with 80 mile per hour winds en route. We look forward to reporting aphid captures from Westby.
Figure: Images of green peach aphid apterae, potato leafroll (PLRV)-infected foliage, mosaic (PVY)-infected foliage, and tubers with 'net necrosis' (a condition caused in some cultivars, most notably Russet Burbank' by infection with PLRV). Images are from the University of California, Statewide IPM Project web site.
Figure: Characteristics of Potato Leafroll Virus and Potato Virus Y
Figure: Principle aphid vectors of potato viruses in Minnesota and North Dakota