NDSU Crop and Pest Report

Entomology


ISSUE 7   June 17, 2004

SLOW ARRIVAL OF CEREAL APHIDS - GOOD NEWS SO FAR

The IPM crop survey program has been in full swing for two weeks. As the southern counties approach boot stage, surveying for aphids is necessary. There have actually been very few detections of cereal aphids by the crop scouts. Of 302 wheat fields surveyed, only one field in Sargent County had detectable levels of aphids, and it was well less than 10% infested stems.

Cereal aphids can arrive in the region from May to July. The greatest risk of yield loss from aphids feeding on grains is in the vegetative (flag leaf) to boot stages. Significant yield reductions after the onset of flowering (or heading) could not be demonstrated in research published from South Dakota in 1997 (Voss et al., 1997. J of Economic Entomology 90: 1346-1350). Reasons for these conclusions were that:

Other components of yield are determined earlier (number of spikelets - determined at jointing; number of seeds - determined at flowering).

To protect small grains from yield loss due to aphid feeding, the treatment threshold is 85% stems with at least one aphid present, prior to complete heading. Fields should be monitored for aphids no later than the appearance of the flag leaf and continue through complete heading.

Small Grain Insecticides for Cereal Aphid Management

INSECTICIDE

DOSAGE IN LBAI/ACRE

PRODUCT PER ACRE

Dimethoate (wheat only)

0.25 - 0.5

0.5 - 0.75 pt

Di-Syston (wheat and barley)
RUP

0.5 - 1

0.5 - 1 pt

Lorsban 4E (wheat only)
RUP

0.25 - 0.5

0.5 - 1 pt

Malathion 57EC

0.9 - 1.25

1.5 - 2 pts

Lannate LV
Lannate SP
RUP

0.225 - 0.45

12 - 24 fl oz
0.25 - 0.5 lbs

Methyl parathion 4EC
RUP

0.25 - 1.5

0.5 - 1.5 pt

Penncap-M
RUP

0.5 - 0.75

2 - 3 pts

RUP - Restricted use pesticide

 

ALFALFA WEEVIL WATCH IS ON

Alfalfa weevils are beginning to make their presence known in the southern and western counties. Discussions with growers have indicated that most of the larvae are still small, 1/8 to 1/4 inch, and feeding in the terminal leaf buds. Damage is visible, holes chewed in leaves or some whitening of top damaged leaves, but minimal by most accounts.

Decisions are being made on whether to treat or cut. If cutting is used as an option be sure to check the swath area for survival of larvae and their potential to damage the regrowth. Treatment guidelines are as follows:

Alfalfa Weevil thresholds

Before 1st Cutting

35% (weak stand) plants with feeding damage

40% (vigorous stand) plants with feeding damage and/or 2 live larvae/stem

After 1st Cutting in stubble

8 or more larvae/ft2, (6/ft2 on sandy soil);
or larvae are suppressing regrowth

Phillip Glogoza
Extension Entomologist
pglogoza@ndsuext.nodak.edu

 

SUGARBEET ROOT MAGGOT:

Peak Fly Activity Expected June 18-28

Moderate numbers of sugarbeet root maggot flies were observed on sticky stakes in old-beet fields on June 15. Fly movement into new-beet fields will continue to progress slowly and will be spread over a longer period than normal due to the cool weather of the past 2 weeks and the expectation of more of the same for the next several days.

Peak fly activity in current-year beet fields should occur between June 18 and 28, depending on location. Be advised that fly emergence and movement into beet fields can be accelerated quickly following a major increase in air temperatures.

Estimated degree-day (DD) accumulations for Friday, June 18 and predicted peak activity dates for sugarbeet root maggot flies in Red River Valley

Site

Air DD
(sine)

Expected date of
peak activity*

Cavalier

422

June 28

Fargo

602

June 18

Grand Forks

520

June 22

Hillsboro

520

June 20

St. Thomas

463

June 25-26

*Peak fly activity in current-year beets is most likely on the first calm or light-wind day to reach 80EF after the required 600 air DD are accumulated.

Growers in high maggot-risk areas (central and southern Pembina County, ND and extreme north central Walsh County, ND) should consider applying a postemergence insecticide. Granular insecticides should work well for postemergence this year for 2 reasons: 1) soils are somewhat moist; and 2) longer residual insecticide activity may be needed because of the delayed buildup of fly activity. Granular products should be applied immediately. It is better to err on the early side of peak activity with granules. The prolonged emergence period will make timing of liquid insecticides more tricky this year. Liquids should be applied at least 3 days before the expected peak to get good results because a lot of fly activity will probably occur for up to 5 days before peaking.

For more information regarding postemergence control of the sugarbeet root maggot and for more specific product recommendations, refer to the “Insect Control” section of the 2004 Sugarbeet Production Guide or the “Sugarbeet Insects” section of the 2004 Field Crop Insect Management Recommendations. These are online at:

http://www.sbreb.org/Production/production.htm
and
http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm

Mark Boetel
Research & Extension Entomologist
mboetel@ndsuext.nodak.edu


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