In this issue

Insect Pest Updates

U of M Plant Disease Clinic Updates

U of M Weed Science Resource

Insect Pest Updates

Bill Hutchison & Eric Burkness, Dept. of Entomology, University of Minnesota

Potato Leafhopper—At Rosemount (Dakota Co.), PLH counts increased significantly this past week, from about 0.5/sweep on June 10th to over 3/sweep on June 26th. This density is well above the thresholds for alfalfa, particularly for new regrowth (< 8””). In addition to checking newly cut alfalfa, growers should also watch for early-season PLH increases in snap beans and potatoes.

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Bean leaf beetle—BLB adult feeding is gradually beginning to subside; however, local infestations can be heavy in selected fields. Our snap bean seed treatment plots continue to be heavily infested, with BLB moving from damaged plots to new plots that are just emerging. Snap bean seedlings appear to be more susceptible to feeding damage than soybean; several plants in the untreated plots have died (apical, growing tip damaged and not recovering). If 15-20% of the plants have exceeded 25% defoliation, and PLH are also present, an early season spray will be needed prior to traditional timing of sprays for European corn borer.

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European corn borer—The ECB first generation flight (bivoltine; 2-generation/yr strain) has been very low, statewide, and is nearly complete. As of June 26th, we had accumulated 800 degree-days (>50F), which is equivalent to ca. 90% the cumulative flight. The highest catch at Rosemount only reached 25/night; this is very low compared to previous years. However, as we mentioned in the June 14th issue, there is considerable potential for the univoltine ECB flight this year, for much of southern Minnesota. For continued updates on ECB flights, see the VegEdge home page at: http://www.vegedge.umn.edu/

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Corn earworm—CEW moth catches in pheromone traps have been very light thus far, as expected this time of year. Traps at Rosemount and Le Sueur (Tom Rabaey) have caught 0-4/night; this should not create significant infestations in early sweet corn. During July, more pheromone traps will be added to the network, with data graphs provided on the VegEdge web site and newsletter.

Striped cucumber beetle—SCB counts of 3 or more/plant continue to be reported in the Twin Cities area, and in southeastern Minnesota. These are very high counts, and much higher than economic thresholds of 0.5-1 per plant. Growers who have not been able to achieve a high level of control may see more bacterial wilt this year. Several labeled insecticides, including Sevin (NOT Restricted Use) and the pyrethroids (e.g., Asana, Capture, Pounce; ALL Restricted Use Pesticides) are very effective. Targeting (banding) the spray over the rows will provide good control. However, growers should also check the calibration of their spray system to ensure the application includes approx. 20 gal. water per acre as well as the correct amount of insecticide.

Organic Growers & Striped cucumber beetle—Although Rotenone has been used for several years for SCB control, this will only provide 50-60% control. Consider using one of the pyrethrum products (e.g., “PyGanic”; McGlaughlin & King Co.) as an alternative. The natural pyrethrum products do not typically last as long as synthetic pyrethroids, but will initially provide a high level of control. Fields should continue to be checked, and subsequent sprays applied every 5 days if beetles continue to invade the field. Once the plants are beyond the 7-leaf stage, and/or start vining and flowering, control of SCB is not necessary. Before applying any product, CHECK with your organic certification group to be sure the product is approved.

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@tc.umn.edu
Jeanne Ciborowski, IPM Program, Minnesota Department of Agriculture, jeanne.ciborowski@state.mn.us
Cindy Tong, Department of Horticulture, University of Minnesota, ctong@extension.umn.edu
Production Editor: Suzanne Wold, Research Assistant, University of Minnesota, woldx018@tc.umn.edu

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Last Revised June 27, 2002.
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