Aphid Alert 2000, No. 1, June 18
During the past two growing seasons, captures of green peach aphid per trap, peaked at levels much above that observed in 1992-1994, years in which we also operated aphid traps in the Red River Valley. The summer of 1993 was unusual in that there was almost no aerial movement of aphids, green peach aphid or any other species, at any location or date. Captures of green peach aphid were consistently higher in 1994 than in1992. The establishment and subsequent predominance of the A-2 mating type of late blight in the Red River Valley has, since 1994, necessitated more intensive use of fungicide in the Red River Valley. That tends to favor green peach aphid (see Lagnaoui et al). In 1998 and 1999, early season rates of green peach aphid capture were not greatly different from that of 1992 or 1994, but aftrer July captures rates were much higher than in our previous study. We suspect that the recent expansion of canola acreage, particularly in North Dakota, favors green peach aphid. This insect does not overwinter in our area. Winged migrants arrive from the south early each spring (they are already present). Canola is a favored host that permits early season increase of this aphid. Canola isn't an source of potato virus inoculum, but it does favor rapid increase of green peach aphid numbers. When these aphids begin to disperse from canola they can acquire and move potato viruses.
Captures of PVY vectors, other than green peach aphid, per trap, 1998 and 1999 compared
Shown (below) are the locations we had traps in 1998 and 1999. When all the traps have been placed for 2000 we will update this figure.
Aphid Alert, a virus vector surveillance program for the Minnesota and North Dakota potato industry, is entering its third growing season. Robert Suranyi, newly minted University of Minnesota Ph.D., will again manage the aphid trapping network and identify the aphids captured. Getting the traps into the field has been delayed in some locations because heavy rains have made access to the fields impossible. Robert and Matt Carroll, second year Ph.D student, are again working out of the Minnesota Department of Agriculture Seed Potato Laboratory in Grand Forks. We will be operating traps at more locations this year, but with fewer traps per location. At each location, we will operate one suction trap and two pan traps. We are pleased to report that since we last reported to you the Rapid Agricultural Response Program administered by the University of Minnesota Agricultural Experiment Station has committed to additional funding to continue our program for two more years.
Both aster leafhoppers and potato leafhoppers are already present on potatoes in the Red River Valley. Adult potato leafhoppers seldom occur in sufficient numbers to cause plant injury, but the threshold for nymphs is very low, e.g., 10 per 100 leaves. We have found that reduced rates (e.g., 1/10 -1/4 label rate) of dimethoate (Cygon) or esfenvalerate (Asana) will give excellent control of potato leafhopper without flaring green peach aphid outbreaks.