MN Fruit & Vegetable IPM News - Vol. 1, No. 4

Potato Leafhopper (Empoasca fabae, PLH): We are just beginning to detect PLH activity in alfalfa. On May 25 we found 0.02 adult PLH/sweep in 10-12 inch tall alfalfa near Rosemount, MN. Fritz R. Breitenbach, IPM Specialist, in southeastern MN (Olmsted Co.) also confirmed a low-level flight of PLH this week in 15” alfalfa. These levels are below treatment thresholds of 2 PLH/sweep for this height alfalfa. In addition, most alfalfa in southern MN should be ready to cut within the next 8-12 days and treatments on the first cutting will not be needed. However, the regrowth, and NEW seedings this spring, will be susceptible to PLH feeding, and should be watched closely. Since PLH are now present in the state, monitoring of vegetable crops, such as snap beans, should begin. Treatment thresholds for PLH in snap bean are 0.5 PLH/sweep up to the 3rd trifoliate, and 1 PLH/sweep for plants at the 3rd trifoliate and larger. For information on treatment thresholds for PLH, see the VegEdge Fact Sheet at: http://www.vegedge.umn.edu/vegpest/plh.htm

Bean Leaf Beetle (Cerotoma trifurcata, BLB): BLB activity in snap beans is continuing to increase. On May 25 th, we took note of BLB feeding damage in our snap bean seed treatment plots, using a rating scale of 1-7 (where 1 = dead plant, and 7 = no damage). In plots where seed was treated only with fungicide, ratings were between 4 and 5 (4 = >11 holes/leaf and less than 90% defoliated; 5 = 6-10 holes/leaf). In plots where seed was treated with an insecticide, damage ratings were between 6 and 7 (6=<5 holes/leaf, 7= no damage). Individual plants in fungicide-only plots had 1.13 BLB/ 5 plants, while plants where the seed was treated with an insecticide had no BLB. As stated last week, control should be considered if more than 10% of the seedlings in the cotyledon to first-trifoliate stages exhibit more than 25% defoliation (e.g., 6-10 "shot-holes" per leaf).

Striped Cucumber Beetle (Acalymma vittatum, SCB): Populations of SCB in cucurbits (squash, cucumber, pumpkins, melons) in the Rosemount area (Dakota Co.) are low, with the first SCB detected in traps on May 25 th. Seeded plantings in the Rosemount area are at the cotyledon growth stage. However, in southeastern MN (near Rushford), where squash is at the 3-leaf stage, a grower reported having up to 4 SCB/plant. Newly emerging cucurbits are very susceptible to direct feeding damage, specifically cotyledon to the 3-leaf stages. In addition, at these early growth stages cucurbits are most susceptible to bacterial wilt (cucumbers and melons are generally more susceptible than squash and pumpkin), which can be transmitted by the beetles. Unfortunately, we do not currently have many control options to choose from for SCB management. Please check for labeled insecticides for each crop. For more information on SCB and treatment thresholds, see the May 19, 2000 VegEdge article at http://www.vegedge.umn.edu/mnvegnew/vol2/vol2no5.htm.

See also the VegEdge Fact Sheet at: http://www.vegedge.umn.edu/vegpest/cucs/scb.htm

Editor’s Note (unrelated to vegetables): Fritz Breitenbach, Rochester area, also found very high infestations of alfalfa weevil in several alfalfa fields, the highest he has observed in 7-8 years. Because alfalfa will soon be cut, this should not be an immediate concern. However, alfalfa regrowth should be watched closely for surviving larvae that could do considerable damage to the regrowth. In contrast to much of the extension publications, cutting alone does not always effectively control AW larvae in MN; this is likely due to the mild/cool temperatures and/or high RH we can have in late-May to early-June, compared with warmer/dryer conditions in states south of us. If growers are not seeing normal “green up” within 5-7 days after harvest, they should consider alfalfa weevil, clover leaf weevil and/or various cutworm spp. as likely sources of damage. For more information on monitoring and thresholds for alfalfa insects, see the fact sheet: “Alfalfa IPM: Sampling Alfalfa Insects” (FO-3516-GO; 1993) at: http://www.extension.umn.edu/distribution/cropsystems/DC3516.html

**Have a Great Memorial Day Weekend**

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ACKNOWLEDGEMENTS

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@umn.edu
Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Division,jeanne.ciborowski@state.mn.us
Suzanne Wold-Burkness, Department of Entomology, University of Minnesota, woldx018@umn.edu

The Newsletter is published weekly from May through August, cooperatively, by the Minnesota Department of Agriculture (MDA) and the University of Minnesota (U of MN). Reports are posted on the U of MN and MDA web sites on Fridays. If you have suggestions and/or comments, please send your contributions by 4 p.m., Tuesday to Jeanne Ciborowski, 651-297-3217, jeanne.ciborowski@state.mn.us , MDA, 90 W. Plato Blvd., St. Paul, MN 55107-2094. You can access the Newsletter at the U of MN web site in htm. format at: www.vegedge.umn.edu/MNFruit&VegNews/mnindex.htm and at the MDA web site in pdf. format at: www.mda.state.mn.us/biocon/fruitreports/default.htm

Partial funding for this publication is provided through partnership agreements with the Minnesota Fruit and Vegetable Growers Association and the United States Department of Agriculture – Risk Management Agency (RMA) and the RMA Community Outreach and Assistance Partnership Program. These institutions are equal opportunity providers.

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Last Revised May 27, 2004.
The University, including the Minnesota Extension Service, is an equal opportunity educator and employer. ©1999-2004 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.