NDSU Crop and Pest Report

Entomology


ISSUE 9  July 1, 2004

SOYBEAN APHID UPDATE

Here we are in the last week of June and waiting on the first reports of aphids. In our region, the first reports of finding soybean aphid have usually occurred by this time the last two years. In southern Minnesota, they typically had found them by now also, but the most recent report has indicated no detections, yet. Expect this to change very soon. People who are looking closely are likely to find some aphids soon, but probably in very specific situations.

Source: Minnesota Pest Report.  Volume 4, Issue 4, June 25, 2004.

Where are we most likely to find aphids first ?

North Dakota soybean aphid research project has looked at colonization of fields for two years now. The general trend we have seen is that in our flat, open landscape the aphids are initially colonizing fields near shelterbelts, southern field edges, or perhaps some other protective structure.

Fields at greatest risk to colonization are those in very close proximity to wooded areas where buckthorn, the overwintering host plant where eggs of the aphid hatch in the spring and get the population started, is growing. Particular attention should be given to smaller fields (less than 30 acres) that are surrounded by wooded areas. Several areas in the valley where detections occur first were smaller fields near waterways. These river areas are wooded and are suitable habitat for the buckthorn, and when surrounding smaller fields, the aphids have had good opportunity to colonize fields early.

Check field edges first to detect the earliest colonization. Our surveys indicate that it takes about 3 to 4 weeks for aphids to be detected in other areas of the field. Eventually, the larger colonies develop where initial colonization occurs.

Within our region, Fergus Falls, Minnesota is one area to pay close attention. For the past two seasons, some of the larger infestations of soybean aphid have occurred in this area, infesting plants in the early reproductive stages by mid to late July.

The NDSU Crop survey will begin sampling soybean fields next week to detect populations and determine how they might progress this season.

 

UNIVOLTINE CORN BORER EMERGENCE DELAYED

Degree days for corn borer are accumulating slowly, also. Corn growth has equally been affected. Here is the degree day model developed to predict occurrence of the univoltine flight of corn borer moths. As with other degree day models, it should help us identify priority times for field scouting. The models pinpoint the occurrence of key biological events. In this case the model is indicating the proportion of moths that have emerged based on temperatures.

Degree Day (Modified Base 50EF) Model for Moth
emergence of Univoltine-type European Corn Borer

Accumulated
Degree Days

Proportion of Emerged Moths

911

10 %

986

25 %

1078

50 %

1177

75 %

1274

90 %

Current degree day accumulations around the major corn production areas would indicate that we are around the 10 to 20% emergence level of moths. By next week, when the 50% level is reached, we should be able to start picking up egg masses in fields.

 

GRASSHOPPER ACTIVITY INCREASES WITH WARM TEMPERATURES

The Crop and Pest survey scouts are detecting increasing numbers of grasshoppers throughout the state. With the warmer temperatures, hatching has increased and many small grasshoppers are now showing up in field borders and edges.

The southwest quarter of the state has had some of the greatest numbers this past week. Reports from other areas indicate increased concerns also, including some hatching within fields where late season crops were growing last summer, attracting adults to feed and females to lay.

 

WHEAT MIDGE DEGREE DAYS ACCUMULATE SLOWLY

In recent years, emergence predictions for wheat midge would already be made. However, with the cool spring, midge development has been delayed. A check of the midge degree day (DD) accumulations reveals that we have just reached the 1300 DD in the southeast corner of the state. This same level may not be reached for another 7 to 10 days further north and west. Daily degree day accumulations have been quite variable, ranging from mid-teens to low-twenties.

 

Phillip Glogoza
Extension Entomologist
pglogoza@ndsuext.nodak.edu


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