NDSU Crop and Pest Report

Entomology


ISSUE 10   July 8, 2004

SECTION 18 EXEMPTION REQUEST FOR USE OF DIMILIN ON WHEAT AND BARLEY
in North Dakota to control grasshoppers

Agriculture Commissioner Roger Johnson has obtained federal permission for North Dakota wheat and barley growers to use Dimilin® 2L to kill grasshoppers. The exemption allows a single ground or aerial application of Dimilin® 2L at a rate of 2 fluid ounces of product per acre. Application may begin when the grasshopper population reaches the second to third instar stage of development. No applications can be made after initiation of wheat or barley boot. Applicators must follow all applicable directions, restrictions, and precautions on the registered product label and have a copy of the exemption label in their possession during application. The exemption, which allows treatment of 2.59 million acres of wheat and 615,000 acres of barley, expires July 15. Dimilin® 2L is manufactured by Crompton Manufacturing Co., Middlebury, CT.

An electronic copy of the label can be obtained at:

http://www.ag.ndsu.nodak.edu/aginfo/pesticid/sec18_2004.htm

 

IPM CROP SURVEY: GRASSHOPPER UPDATE

There was some expansion of the area where grasshopper counts increased near field crop settings. Some higher counts were found farther north, into the north central counties.

The first summary of grasshopper counts from rangeland sites was received this week from the USDA, APHIS-PPQ group in Bismarck. The focus of their work has been the rangeland areas in the southwest. Currently there are a number of spray programs being implemented to address the high numbers of grasshopper nymphs in these sites.

 

CORN BORER EMERGENCE STARTING IN ND

Corn growing degree days reached the 900 DD mark this week, at least in the southeastern counties. This is the point where the single generation (univoltine) corn borer moths begin to emerge. More northern counties will see emergence begin over the next week. Emergence will be well over a couple of weeks due to the gradual accumulation of degree days, currently less than 10 per day. At this rate, it will take almost a week to reach peak emergence in the southeastern counties.

The practical significance of this is that scouting corn for eggs and larvae is still a while off for our corn fields.

 

SOYBEAN APHID SURVEYS FIND LITTLE

As the crop survey program begins to check soybean fields for aphids, little is expected to be found. No aphids were found in fields checked last week in the southern end of the valley. There has been a report of individuals finding some aphids, generally very few when found. The locations were near wooded areas, particularly waterways.

From Minnesota last week, aphid sightings were reported from a number of southern Minnesota locations, but at all locations they were very small colonies ranging from very difficult to find (2 aphids in 5000 plants) to easy to find around New Ulm. (Source: Dave Ragsdale, Entomologist, U of Minnesota)

Potato Leafhopper vs Soybean Aphid

While scouting soybeans for aphids, be sure to recognize the difference between these two insects. The key differences are summarized below.

Soybean Aphid

Potato Leafhopper

yellow

pale green

pear-shaped

longer than wide

stationary

moves sideways rapidly

found in colonies

found separately

Be sure to recognize the difference between the two. Typically, we haven’t seen problems with potato leafhopper in soybean. One published threshold for potato leafhopper in soybean suggests "... 9 leafhoppers per plant for R1-R2 (first bloom) stage soybean." Leafhopper concerns in soybean are most often associated with dry conditions, certainly not an issue at the moment.

 

POTATO LEAFHOPPER IN OTHER CROPS

Dry beans, alfalfa, and potato are affected more seriously by potato leafhopper. They certainly are in the area and these crops should be checked for the presence of the nymphs. The adults are quite mobile and generally pose less of a threat to plants. Nymphs on the other hand are not mobile and will feed on leaves where they hatch. Most control efforts are directed at nymphs because of the greater threat of plant injury that they pose.

 

CEREAL APHIDS STILL LOW IN NUMBER

Infestation levels for cereal aphids are still very low, generally less than 25% of the stems with aphids present. The low populations in the southern counties is good for later planted fields to the north. Without large populations developing in the older grain crops, that will mean fewer aphids migrating northward to the later developing grain fields.

Phillip Glogoza
Extension Entomologist
pglogoza@ndsuext.nodak.edu


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