Aphid Alert 2001, No. 10, August 24
Publication of this issue of Aphid Alert 2001 was delayed due to our webmaster attending the 6th International Aphid Symposium in Rennes, France, 3-7 September, and our aphid identifier developing pneumonia. Not much question who had the better time. However, we are both back at work and expect to soon have Aphid Alert back on schedule.
Aphid captures, week ending August 24
The week ending 24 August saw continued decline in aphid flight activity. Again, no green peach aphid was captured in the trapping network. Captures of aphid species that are potential PVY vectors declined to 6.80 per trap compared to 11.23 the previous week. Across all sampling dates, captures of potential virus PVY vectors in 2001 have been only 1/3 of what they were in 2000. This difference is even more dramatic when we consider green peach aphid flight activity. Green peach aphid captures in 2001 are only 1/180 of what they were in 2000. This should translate into fewer seed lot rejections for virus, especially PLRV this winter.
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)|
Late Blight Summary
Roger Jones, Department of Plant Pathology, University of Minnesota
To see our most recent insecticide trial on green peach aphid, Aphid Alert 2000, no. 7
Minnesota & North Dakota, Aug. 31: Congratulations to all producers for an almost late blight free season. Only three small outbreaks were reported. Much of the credit goes to all of you for following integrated late blight management recommendations all season. Tuber infection and storage problems due to late blight should be minimal, but tuber infection could still be present, so continue late season sprays and monitor the harvest
Wisconsin, Sept 3: The past two weeks has seen a resumption of conditions favorable for late blight. The total number of severity values rose considerably since August 15 and with extensive dew each night, we see additional severity values accumulating each day. In fields in central WI where symptoms of late blight were detected in late June, leaf and stem lesions remained dormant until the past two weeks. Sporulation on some lesions has resumed and secondary spread is being observed where fungicide coverage is not adequate. Many fields have already been treated with vine desiccant in preparation for harvest. Pockets of green leaves and stems remain in many fields, so this is a gentle reminder that late blight is still active and growers need to continue fungicide spray programs as long as foliage and vines remain green. Remember that even small pockets of green foliage infected with late blight pose subsequent risks to stored tubers. The last thing growers need is to inoculate tubers at harvest by running the harvester through these pockets of green vines that have become infected with the late blight fungus late in the growing season. For those fields that will not be vine killed for another two weeks, growers should be especially careful in maintaining a tight fungicide program with thorough coverage of stems and leaves.