Aphid Alert 2001, No. 4, July 13
Aphid Flight Activity during week ending July 13
Aphid flight activity increased over the previous week, but captures remained low at all locations reported. Buckthorn aphid, Aphis nasturii, were caught at several locations. Buckthorn aphid apterae are present in low numbers in some potato fields (e.g., Devils Lake ND, Rosemount MN). Cereal aphids, especially bird cherry-oat, aphid were commonly represented in the week's collections. This increase in cereal aphid capture probably reflects the maturation of small grains in the region causing aphids to seek alternative hosts. The numbers of cereal aphids are still very low, but it is worth noting that in the past, transmission of PVY in seed potato has coincided with the flight activity of cereal aphids in the Red River Valley. Another important crop to pay close attention to is canola, because it can support large colonies of green peach aphid and turnip aphid, Lipahis erysimi. Leaf samples collected from canola fields indicate the begining of population build-up by turnip aphid, but we have not found green peach aphid colonies yet. Sampling of secondary weed hosts of potato virus vector species found large colonies of gooseberry-sowthistle aphid, Hyperomyzus pallidus, on perennial sowthistle, Sonchus arvensis. Although this species is not a known vector of potato viruses, a closely related species, blackcurrant-sowthistle aphid, Hyperomyzus lactucae, that also utilizes Sonchus spp. as a secondary host plant, is a vector of PVY.
Trap locations for which data were not available when this page was created will be updated as results are received.
Aphid captures, week ending July 13. One suction trap and two pan traps are operated at each location, except Crookston, Rosemount and Thief River Falls. Data are reported as total aphid captures per three traps.
No green peach aphids have been reported in the first three weeks of trapping in 2001. In contrast, we began capturing green peach aphid in June in 2000. From previous experience, we anticipate green peach aphid numbers will increase steadily over the next month and peak in early to mid-August. However, we are finding very few green peach aphids on alternative and weed hosts, e.g., canola and wild mustard. Turnip aphid, Lipaphis erysimii, is present at low numbers on canola.
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)|
Key to Identify wingless forms of the MOST COMMON aphids colonizing potato
1a. body outline egg or teardrop shaped, cauda short . . . 2
1b. body outline elongate, antennal tubercles large, pointing outward, cauda long and pointed, cornicles longer than the distance between their bases (Fig. 2a), legs prominent, color green, yellow, or pink, may have a darker dorsal stripe, highly mobile aphids . . . POTATO APHID
2a. body thick, head with prominent antennal tubercles, antennae as long or longer than body . . . 3
2b. body flattened, head without prominent antennal tubercles, antennae shorter than length of body, cornicles almost as short as cauda (Fig. 2b), color opaque lemon yellow to green in color, black in autumn . . . BUCKTHORN APHID
3a. body pear shaped, widest at base of cornicles, antennal tubercles prominent and almost parallel sided, cornicles tapered with prominent flanges on the dark tip (Fig. 2c), color light yellow green to dark green, with dark areas around base of cornicles, legs and antennae with dark joints . . FOXGLOVE APHID
3b. body egg shaped, almost the same width from base of middle legs to base of cornicles, antennal tubercles prominent and pointing inward, cornicles unevenly swollen (Fig. 2d), color light green to almost translucent, pink, or peach, legs and cornicles the same color as the body . . . GREEN PEACH APHID
Figures adapted from MacGilliivray, 1979. Aphids infesting potatoes in Canada: a field guide.
Late Blight Reported in Area
Roger Jones, Department of Plant Pathology, University of Minnesota
In Minnesota, Cumulative Severity Values have been exceeded and spray programs should have been initiated in: Brooten, 7/9, Foxhome, 7/9, Humboldt, 7/2, Little Falls, 6/15, Park Rapids, 6/11, Warren, 7/3.
Late blight has been found in Wisconsin. As of June 20, late blight has been reported in five production fields near Hancock, one field near Bancroft, two fields near Ellis, as well as in Amherst and Plover, WI. (Wisconsin late blight update)
Late blight has been found in Michigan. As of June 25, late blight has been reported in one production field near Entrican, MI.
If you find something that you think might be late blight, please contact Roger Jones at the University of Minnesota at 612-625-5282.