In this Issue:


Vegetable Insect Update


Strawberry IPM Update


Excerpt from: When to Prune Out Fire Blight: To Prune or Not to Prune

Weekly Trap Counts: July 11 - July 21, 2005


PLEASE NOTE:  The Newsletter will not be published for the next 2 weeks.  The next Newsletter will be available on August 12.

Insect, Pest Fact Sheets

Vol 2 No.11   July 25, 2005

Vegetable Insect Pest Update

Eric Burkness, Suzanne Wold-Burkness, & Bill Hutchison, Dept. of Entomology, University of Minnesota, St. Paul

Cabbage Looper (CL): This week we observed a dramatic increase in CL larval infestations in Rosemount, with an infestation level of 88% (treatment threshold = 10%) in vegetative (6-8 leaves) cabbage. In addition, CL moth catch in pheromone traps has increased slightly. In this situation, treatment of the field as soon as possible is critical because the majority of CL larvae are small (easier to control), and an infestation this high on small plants could greatly reduce yield, or cause plant mortality if left untreated. All cole crops (cabbage, broccoli, cauliflower, etc.) in southern Minnesota should be checked carefully this week for looper infestations.

PLH feeding damage (click to enlarge)Potato Leafhopper (PLH): PLH nymph counts remain at 1.8 nymphs/leaflet. Plants are beginning to show signs of PLH feeding with curled leaf margins (see photo). Fields that are more than one week from harvest should continue to be monitored for PLH nymphs and adults.


Corn Earworm (CEW): Sweet corn fields that are beginning to silk should be watched closely for CEW egg-lay. Although CEW moth catches remain low across the state, we have had a recent report of CEW larval infestations in mature sweet corn ( Austin, MN).

European Corn Borer (ECB): The ECB moth catch remains low across the state with the exception of a few locations. St. James (Watonwan Co.) and Jeffers (Cottonwood Co.) have reported high ECB moth catches for the time period of July 9- July 16 (>100/night at St. James, >50/night at Jeffers). Trap catches after those dates have decreased dramatically (<10/night). Moths caught at these locations are most likely the univoltine strain of ECB. As stated in the July 11 th issue of the newsletter a univoltine flight >20 moths/night, for several nights, could result in egg-lay on tasseling or silking corn (i.e., >4% of plants with egg masses), which could result in significant ear infestations.

Adult corn rootworm feeding damage resulting in poor pollination  (click to enlarge)Western and Northern Corn Rootworm (CR): Adult corn rootworms are beginning to emerge and there is the potential for adults to move into sweet corn fields that have fresh silk. Fields with fresh silk should be monitored for silk clipping. Clipping by corn rootworm adults can interfere with pollination, resulting in poor kernel fill (see photo). The risk to pollination is likely to be a primary concern within the first 4-6 days of silk emergence. Research is underway this year to more clearly quantify this risk.

WBCW eggs (click to enlarge)Western Bean Cutworm (WBC): As in recent years, WBC moth counts began to increase slowly for selected MN light traps. However, counts remain very low to date. Previous work in Nebraska and Colorado indicate that based on pheromone traps, cumulative moth catch/trap must be between 700-1000 for a moderate risk of larval damage in field corn or dry beans. Catches over 1000 are needed to indicate high risk potential. Thus far in Minnesota, since 2001, we have not approached these numbers. However, different pheromone traps have been used in the various studies, and very little work has been done to relate moth catch with infestation risk to sweet corn, or snap beans. Sweet corn growers in Idaho have traditionally used an action threshold of 2-4% of the plants infested with egg masses (see photo) or recently hatched early-instar larvae, when tassels are emerging. Until we have more information about the infestation potential for vegetable crops, we will continue to recommend this threshold. (A similar threshold for field corn is 8% of the plants infested). For more information on WBC, view the following:

Article by Dr. Marlin Rice, ISU:

WBC Light Trap Network in Minnesota:





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Co-Editors: Bill Hutchison (, Department of Entomology, University of Minnesota, Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Management and Development Division, and Suzanne Wold-Burkness (, Department of Entomology, University of Minnesota

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., Wednesday to Jeanne Ciborowski, 651-297-3217, , 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: and at the MDA web site in pdf format at:

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