Aphid Alert 2001, No. 3, July 6
Aphid Flight Activity during week ending July 6
Aphid numbers are still very low at all locations reported. No green peach aphid were captured, but they were detected on foliage when scouting potato plants at Park Rapids.
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 6. 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.
Colorado potato beetle
Our old nemesis, Colorado potato beetle, Leptinotarsa decemlineata (Say), is active throughout the region. Colorado potato beetle is most effectively controlled with systemic insecticides applied at planting, or foliar insecticides applied immediately after egg hatch. In southern Minnesota, larvae of the first summer generation are mostly late instars(3rd and 4th) or have already entered the soil to pupate. In the Red River Valley, egg laying is still occurring and in most fields larvae are still early instar (1st and 2nd). This is the best time to spray, before significant defoliation has occurred, and while the larvae are most susceptible to insecticide.
Potato Leafhopper, Empoasca fabae (Harris), are present in exceptionally high numbers in eastern and central Minnesota. They are reported as present in low numbers in northern Minnesota and eastern North Dakota.
Potato leafhopper control is essential because this is one of the most damaging of all insect pests of potato. The injury caused by potato leafhopper is irreversible damage to the phloem. Visible damage is called hopperburn. Injured leaves show a marginal necrosis and often cupping and yellowing. By the time symptoms of hopperburn are seen, the phloem is severely damaged. Yield reduction can approach two-thirds and the remaining tubers will not size properly.
You should not wait for symptoms to appear before treating for potato leafhopper. Fields should be scouted now and weekly hereafter. The economic threshold of potato leafhopper in potato is 10 nymphs on a sample of 100 leaves taken from the middle portion of the canopy. Most insecticides are highly effective against potato leafhopper. Generally, treatments applied for control of Colorado potato provide excellent control of potato leafhopper.
However, seed potato growers may benefit from using reduced rates of insecticide to control potato leafhopper. We have achieved excellent control of potato leafhopper nymphs with 1/4X label rates of dimethoate (Cygon), i.e., 0.125 lb AI/acre. The advantage, other than cost of application, is that reduced rates of dimethoate do not flare green peach aphid outbreaks - whereas most general purpose insecticides (i.e., other than effective aphidicides) tend to do so.
Late Blight Reported in Area
Roger Jones, Department of Plant Pathology, University of Minnesota
Late blight has been found in 5 areas of Wisconsin and in one production field in Michigan. As of July 4, late blight alert warnings were issued for Humboldt and Warren, Minnesota. On June 15th, late blight alert warnings were issued for Park Rapids and Little Falls, Minnesota.
Although our models do not take innoculum levels into consideration, the weather has been favorable for late blight to begin spreading. Please take appropriate precautions and scout your fields frequently.
If you find something that you think might be late blight, please contact Roger Jones at the University of Minnesota at 612-625-5282.