Aphid Alert 2001, No. 9, August 10
Aphid Alert 2001 will not be published on the WWW or sent to e-mail subscribers again until September 14. However, we will continue to update reporting of aphid captures on this web site as that data becomes available. To view updated aphid capture data bookmark this page.
Aphid captures, week ending August 17
This week's aphid flight activity remained low in comparison to 2000. No green peach aphid were reported collected as of August 17 at any of the trapping locations. Essentially, green peach aphid has not been a factor this year. Most prevalent of potential PVY vectors were corn leaf aphid, Rhopalosiphum maidis (Fitch), bird-cherry oat aphid, Rhopalosiphum padi (L.), English grain aphid, Sitobion avenae (Fabricius), and the sunflower aphid complex, Aphis helianthi Monell. Turnip aphid, Lipaphis erysimi (Kaltenbach), was only reported at Linton, ND. Aphid pressure has been uncommonly low this year so seed potato growers have reason for optimism that this year's winter tests will bring better news.
Growers in the Red River Valley are beginning to vine kill. Some will begin digging next week. Risk of late blight remains very high. On August 17, NDSU plant pathologists Neil Gudmestad and Gary Secor confirmed the first 2001 instance of potato late blight in the Red River Valley. That occurred near Lisbon, ND.
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.
Captures of green peach aphid per trap, 1992-1994, 1998-2000.
Abundance of green peach aphid has differed greatly from one year to the next. In the years 1992-1994 (green lines), captures of green peach aphid were consistently low; in 1993 only 7 were captured all year. In 1998 and 1999 (red lines) , mean weekly captures were 6 times that of 1992-1994. In 2000 (yellow line), the mean weekly capture rate was comparable to that of 1992 and 1994. Peak green peach aphid flight activity occurs in early-mid August, about one week after peak flight activity of other potential PVY vectors.
Comparison of captures of green peach aphid per trap in 2000 and 2001.
We can now say that 2001 was a repeat of 1993, a year with essentially no green peach aphid flight activity. The canola is mostly harvested and never supported the large populations of green peach aphid or turnip aphid that were common in 1998-2000.
Captures of PVY vectors other than green peach aphid per trap, 1992-1994, 1998-2000.
Abundance of potential PVY vectors other than green peach aphid have differed greatly from year to year. Total captures in 1998 were 20 times that of 1993, and 2-3.5 times that of other years. Species predominance differed among the years but there were also differences among locations. Combining data from all dates and trap locations, the most abundant aphid in 1998 was the sunflower aphid complex, (70% of total captures). In 1999 the most abundant species was the turnip aphid, (25% of total captures). In 2000 the corn leaf aphid comprised 35% of total trap captures.
Comparison of captures of potential PVY vectors (other than green peach aphid) per trap in 2000 and 2001.
Corn leaf aphid continues to be the most abundant aphid in trap captures. We are capturing only small numbers of bird-cherry oat aphid, English grain aphid, greenbug, and sunflower aphid. We have captured very few turnip aphids.
Guide to the Field Identification of Wingless Aphids on Potato
|Potato Aphid, Macrosiphum euphorbiae (Thomas)||Buckthorn Aphid, Aphis nasturii (Kaltenbach)||Foxglove Aphid, Aulacorthum solani (Kaltenbach)||Green Peach Aphid, Myzus persicae (Sulzer)||Cotton (=melon) aphid, Aphis gossypii (Kaltenbach)|
Soybean Aphid, Aphis glycines Matsumura, continues to spread across Minnesota. However, heavy infestations are confined to the southeastern portion of the state.
Most registered insecticides performed very well in a recently completed University of Minnesota soybean insecticide trial. Some growers reported poor control with pyrethroids applied when air temperatures were very high.
For more information on soybean aphid in Minnesota view the Minnesota Pest Report, August 17 (PDF)
To see our most recent insecticide trial on green peach aphid, Aphid Alert 2000, no. 7
Late Blight Alert!
Roger Jones, Department of Plant Pathology, University of Minnesota
Minnesota: The good news is that there are still no reports of blight. With harvest just around the corner, this season's crop has been through a lot. The most evident of this is in the East Grand Forks, Grand Forks and Thompson area, which have been hit with localized rain and wind that plagued the valley last week. According to Duane Preston, Extension Agent-Potatoes UMN/NDSU, the East Grand Forks, Grand Forks, Thompson area has been "severely hurt with excess water." The outlook in Clay County is the opposite; conditions there are dry and in need of rain. While Walsh County is advancing well there are some signs of flea beetle damage. The crop in this area is in excellent condition. Nearly all regions of Minnesota have now experienced ideal conditions for the spread of late blight. Please keep a close watch!! Scout your fields and continue your spray program. Do not hesistate to contact Roger Jones (1-888-335-8636) if you have concerns.
North Dakota: Late blight has been confirmed near Lisbon in southeastern ND. Growers in this area should scout fields, continue fungicide application and have Curzate available to mix with their protectant fungicide if thunderstorms move through this area. If late blight is found, please send samples to Plant Pathology, NDSU for confirmation and genotype determination. Conditions for late blight remain favorable in all irrigated sites and for Stephen and Prosper at the non-irrigated sites, but for the other non-irrigated sites, conditions remain unfavorable for late blight development the past few days. Conditions have been quite favorable for early blight, and despite repeated applications of fungicide, early blight seems to continue. Additional fungicide applications or the addition of a tin-based fungicide may help with the late season early blight.
Wisconsin: The humid and cooler weather of the past week provided favorable conditions for additional spread of late blight. IPM scouts are reporting additional fields with symptoms of late blight. While the general scenario is a few infected leaves here and there, the distribution of late blight throughout central Wisconsin is a concern. Long periods of high relative humidity and leaf wetness could pose problems for containment of late blight as we move into the last month of maintaining foliage health. The area of late blight concern also continues to expand with late blight as far south as Coloma and north to the Antigo area. Fungicide spray programs should continue on a 5-7 day interval until vine kill. For the most part, control of late blight has been excellent. This was achieved by careful, but not excessive use of fungicides to maintain protection of all foliage as we have moved through the growing season. Severity values have increased substantially during the past week, especially in northeastern WI. Growers should plan their spray programs accordingly.