In this issue

Feature Article: Cabbage Looper Takes Off!

Minnesota Vegetable IPM Field Day

Plant Disease Clinic Update - Sample Guidlines

Potato Leafhopper Infestations on the Rise!

Cabbage Looper takes off!

Bill Hutchison and Eric Burkness, Dept. of Entomology, Univ. of Minnesota, St. Paul, Minn.

Cabbage looper larva	Cabbage, Broccoli and Cole Crops: View this as an early warning forecast for significant cabbage looper (CL) infestations, for the next 3-4 weeks. We have observed a dramatic increase in CL egg-lay during the past 5 days, at both Rosemount and Apple Valley (Dakota Co.) and in southeastern Minn. (Houston Co.). At most sites, 75-80% of the cabbage plants are infested with CL eggs, averaging 3-5/plant. We also have moderate levels of imported cabbageworm (ICW) and diamondback moth larvae (DBM) (see photos).
Imported cabbageworm larvae	At this time, growers have 4-6 days (depending on temperature) to begin to make treatment decisions. With CL and ICW, there is usually significant natural larval mortality in the 1st and 2nd instar (i.e., <1/4 to 3/8 inch size). Our experience over the past 5 years has shown it is best to wait about 4-5 days after the eggs begin to hatch, and re-sample to verify that the larval infestation is >10%; if so, then spray at this time, and re-check fields in 5-7 days.
Diamond back moth pupa (top) and adult (bottom)	Egg lay and larval infestations for both CL and ICW can be expected to continue to increase. Fields should be monitored 1-2 times/week to determine infestation levels of CL, ICW, and DBM. Diamondback moth larval infestations are at 10-20%. However, parasitized diamondback pupae have been found and parasitism rates can reach up to 90%, which should hold populations under threshold. Treatment decisions should therefore be based primarily on the presence of the looper, the most damaging of the three pests, and ICW. Thresholds are also dependent upon the plant growth stage. The following thresholds have worked well in recent IPM implementation studies at Rosemount and Apple Valley, Minn.

Control: Many insecticides are now labeled for the larval pest complex on cabbage and the related cole crops. The following table (click here to view table), based on data collected in 2000, provides a good overview of some of the control provided by several registered insecticides. As expected, the pyrethroids (Warrior and Capture in this data set) provide good control of the entire pest complex. SpinTor (spinosad) is one of the new "alternative" products that also provides reasonable looper control, yet also conserves more beneficial insects (e.g., for aphid control, etc.), compared with the pyrethroids. Dipel ES is one of the conventional Bt (Bacillus thuringiensis) products that provides reasonable control, if applied often enough (every 5-7 days for looper control). Dipel should still have organic certification (but check local certification lists).

For more efficacy data on the cabbage insect complex, see the October 22, 1999 article at: http://www.vegedge.umn.edu/mnvegnew/vol1/cab1014.htm

See also cabbage pest fact sheet at: http://www.vegedge.umn.edu/vegpest/colecrop/cclist.htm

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 Specialist, University of Minnesota, woldx018@tc.umn.edu

Disclaimer
Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current directions of the manufacturer

Last Revised July 12, 2001.
The University, including the Minnesota Extension Service, is an equal opportunity educator and employer.©2001 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.