Aphid Alert 2001, No. 8, August 10
Aphid captures, week ending August 10.
We have completed our eighth week of aphid trapping for 2001.
The past week has been marked by continued extreme heat and violent storms across the Red River Valley of the North. Several locations experienced straight line winds of 100 miles per hour and very heavy rain. Many fields have been lost or damaged by standing water. Green peach aphid, Myzus persicae, and turnip aphid, Lipaphis erysimi, appear to have fared badly under such adversity and now with canola harvested or senescing, this source appears largely eliminated. For potato growers, late blight must now be their first concern. If late blight infection occurs in the region, the risk of spread would be very high.
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.
Summer 2001 is becoming a repeat of 1993, a year with essentially no green peach aphid flight activity. Recent heavy rains and hot temperatures appear to have all but eliminated green peach aphids on canola and removing that threat. We do not anticipate that captures of green peach aphid will increase appreciably over the next several weeks.
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 Aphis helianthi Monell, (70% of total captures). In 1999 the most abundant species was the turnip aphid, Lipaphis erysimi (Kaltenbach) (25% of total captures). In 2000 the corn leaf aphid, Rhopalosiphum maidis (Fitch) 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, Rhopalosiphum maidis, continues to be the most abundant aphid in trap captures. Some locations have high densities. We are capturing only small numbers of bird-cherry oat aphid, Rhopalosiphum padi, English grain aphid, Sitobion avenae, and greenbug, Schizaphis graminum We have captured very few turnip aphids, Lipaphis erysimi.
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)|
Insecticide Trial for Soybean Aphid, Aphis glycines Matsumura, 2 August 2001
Caution: This information applies to soybean aphid and should not be used to select insecticides for aphid control on potato. To see our most recent insecticide trial on green peach aphid see Aphid Alert 2000, no. 7.
For more information on soybean aphid in Minnesota view the Minnesota Pest Report, August 10.
Results: Most registered products tested gave satisfactory control of the soybean aphid. Two compounds, Pounce and Dimethoate, significantly provided only 85-90% control of the soybean aphid. In general, 95% control or above is needed to prevent resurgence of the aphid population following treatment. As with all aphid control, better results are achieved with high pressure and high volume. Here we used 42 psi and 30 gallons of spray solution per acre. Our plots also lacked a closed soybean canopy allowing for good penetration of insecticide into the lower canopy. All products gave equivalent control of soybean aphids whether in the top or lower canopy.
We tested all products at the highest labeled rate. It is our opinion that those products that gave near 100% control could be used at the lowest labeled rate and still achieve satisfactory control (>95%). The key to good aphid control is less dependant upon rate than on using adequate spray volume (at least 20 gallons per acre) and high pressure (40-80 psi).
Late Blight Alert!
Roger Jones, Department of Plant Pathology, University of Minnesota
Minnesota: Temperatures across Minnesota have been extremely hot for the past couple of weeks. The region has been recently swept by violent storms and much rain. Many fields have standing water and the air is very humid. Nearly all regions of Minnesota have now experienced ideal conditions for the spread of late blight. No late blight has been reported in Minnesota, but 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. The following MN locations have attained late blight alert status: Alexandria and St. Cloud (Aug. 2), Becker (July 30, Hollandale (July 28), Perham, Staples (July 20), Baudette, Crookston, Eldred, Felton, Karlstad, Stephen, Williams (July 16 & 18), Brooten, Foxhome (July 9), Humboldt (July 4), Warren (July 3), and Little Falls, Park Rapids (June 15).
North Dakota: Recommendations as of Aug. 8: Late blight favorability values have become negative the past five days due to the hot weather. Hot nights limit the sporulation and spread of late blight, but do not kill it. It can remain viable in the plant until cool wet weather reappears. The forecast calls for cooling temperatures for the next few days, which will provide conditions more favorable for late blight. We still do not have late blight reported in our region, but growers should continue to do the big three management practices: scout fields, monitor the weather, and apply fungicides regularly. The weather continues to be the dominant factor influencing potato production, resulting in drown outs, hail damage, wind damage and flooded fields. Remember to disc up damaged fields and apply fungicide to abandoned fields.
Wisconsin: The rains have resumed and pose a threat of 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 WI poses 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 is 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.