Aphid Alert 2001, No. 7, August 3
Aphid captures, week ending August 3
We have completed our eighth week of aphid trapping for 2001. We still can only report the capture of one lone green peach aphid (last week at Baker). The same situation exists in Scotland. The July 22 Scottish Aphid Bulletin reports "The summer goes by but still the aphids in Scotland refuse to fly. " In view of the low level of potato aphid activity, and the low level of activity of other aphid species that vector non-persistent viruses, aphid monitoring in Scotland was ended for 2001 as of July 31. In the northern U.S., the 2001 growing season has had few wind events favorable for the long-distant transport of green peach aphids to the northern Great Plains (see MinDexAphid Alert 2001, No. 5, July 20 in Aphid Alert no. 5). We are finding green peach aphid and turnip aphid, Lipaphis erysimi, on canola and other brassicas, but numbers are low compared to the past three years. Corn leaf aphid, Rhopalosiphum maidis, has been the most abundant aphid in our trap collections. The total of aphids other than green peach aphid captured in 2001 is less than on the same date in 2000. The species complex is different between the years with many more corn leaf aphid and fewer turnip aphid in 2001. The past week has seen very heavy rainfall throughout much of the Red River Valley region of Minnesota and North Dakota. Many production fields have been lost or damaged by standing water. Indeed, we have lost many of our experimental plots. For potato growers, late blight must now be their first concern. If late blight infection does occur in the region, the risk of spread will 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.
This year is shaping up to be a repeat of 1993, when there was essentially no green peach aphid flight activity all summer. Still, we urge caution. Much virus infected seed was planted this spring by commercial growers. We have to assume that even with low vector numbers the risk of virus spread to seed fields remains high. Since July 23, we have observed a 5-fold increase in green peach aphid numbers on canola. We expect green peach aphid flight activity will pick up with the onset of canola harvest. Thus, growers should scout their fields frequently (at least twice a week), especially on field margins and corners, to detect colonization. Remember that green peach aphid favors the underside of lower leaves of the plant. Focus scouting on the lower third of the potato plant. When green peach aphid densities reach the threshold of 3 wingless green peach aphids per 100 leaves insecticides should be applied to prevent the spread of PLRV. However, the most effective method to reduce spread of both PVY and PLRV spread is to kill the vines as early as feasible.
Corn leaf aphid, Rhopalosiphum maidis, was abundantly represented in trap captures at most locations. Small grains are ripening across the northern Great Plains, but apparently these crops supported few aphids this year. We continue to catch only small numbers of bird-cherry oat aphid, Rhopalosiphum padi, English grain aphid, Sitobion avenae, and greenbug, Schizaphis graminum Canola harvest should be underway next week. With the maturing of canola, we anticipate increased flight activity of turnip, Lipaphis erysimi and green peach aphid. Soybean aphid, Aphis glycines, continues to spread quickly across the state. In southeastern Minnesota (from Minneapolis south and east) virtually 100% of the plants are heavily infested (100 or more aphids per terminal). Plant injury is common. Insecticide trials recently completed suggest that most organophosphate insecticides registered for use on soybean give excellent control, but that pyrethroids do not perform well, especially when it is hot.
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)|
Joseph Munyaneza, David W. Ragsdale, Edward B. Radcliffe, and Andi Nasruddin
Department of Entomology, University of Minnesota (experiment reported in Arthropod Pest Managment, 2001, ESA)
A green peach aphid control experiment was conducted at Rosemount, MN in 2000. NewLeaf Russet Burbank potatoes were used to eliminate Colorado potato beetle as a factor in the experiment. Starting June 22, all plots received a weekly application of the fungicide Bravo Zn to prevent late blight and weekly application of Guthion 50WP to control potato leafhoppers and increase green peach aphid densities.
Aphidicides were applied 9 Aug using a tractor-mounted Brittonya boom sprayer with 3 drop nozzles per row and delivering 33 gal/acre at 45 psi. Sampling involved counting aphids on 35 mid-potato plant leaves per plot. Plots were replicated 4 times per treatment.
Monitor 4EC provided excellent control within 2 d of treatment. High rates of Actara 25WG and Provado 1.6F were effective 5 d after treatment. Fourteen days after treatment, Actara 25WG, Fulfill 50WG, and Monitor 4EC were providing best aphid suppression.
To read more about Fulfill insecticide and managing insecticide resistance in potato aphids read the interesting article by Andy Evans of the Scottish Agricultural College.
Late Blight Alert!
Roger Jones, Department of Plant Pathology, University of Minnesota
Minnesota: Growers of the region must be commended for their vigilant late blight control program since no late blight has been found in the Red River Valley yet. Unfortunately, the torrential rainfall of 31 July (ranging from 1.5 inches in Nielsville, (MN) to over 6 inches in Baudette (MN) caused field conditions that could delay this week’s scheduled fungicide applications with a ground sprayer. Weather conditions are very favorable for late blight infection. We strongly recommend you avoid any skip in the late blight program and apply fungicides by air. Special attention should be placed on low lying areas of fields where plants are under the most stress and thus most susceptible to late blight infection. Disking these areas under or treating them with vine kill chemicals could prevent establishment of late blight in the field. The following MN locations have attained late blight alert status: 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). The weather has been favorable for late blight to spread. Please take the appropriate precautions and scout your fields frequently.
North Dakota: Cumulative severity values as of July 25 for irrigated sites ranged from 64 (Linton) to 104 (Robinson), and for nonirrigated sites from 62 (Stephen, MN) to 950 (Warren, MN). Call NDSU Potato Late Blight Hotline at 1-888-482-7286.
Wisconsin: Cumulative severity values as of July 25 ranged from 44 at Hancock to 107 at Plover. Late blight is currently confined to an area of central WI that stretches from Coloma to Plover. The extent of the area is a concern for all growers in this area of the state. At this point in the season, no late blight has been reported from northwest, northeast, southwest, south-central or southeast WI. Growers continue to spray production fields on 5-7 day intervals. Now that weather conditions have returned to a more normal pattern with periodic rainfall and somewhat cooler temperatures, we can expect an increase in disease pressure. See Wisconsin web site for recommendations for your area.
Michigan: Late Blight has been found in Montcalm County at the following locations (and approximate number of infected fields) as of 7/30/01: Cedar Lake(2), Vestaburg(3), Lakeview Area(8), Edmore(3). If late blight has been found within 2-5 mi of your fields, apply systemic fungicides at full recommended application rate or protectant fungicide plus Supertin at 3 - 3.75 oz/acre -- minimum 7 day application interval. If late blight has been found within 1 mi, shorten interval between applications to maximum of 5 days. For more detailed information about your location visit Michigan State University, Late Blight Lab web site.