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ISSUE 4    May 25, 2006

MANITOBA INSECT AND DISEASE UPDATE

Another weekly pest update newsletter of interest is the "Manitoba Insect and Disease Update" from entomologist, J. Gavloski, and plant pathologist, D. Kaminski, of Manitoba Agriculture, Food and Rural Initiatives. Producers, agents, ... located in northern counties of North Dakota will especially be interested. Observations on insect and disease activity or control are reported for Manitoba. Please see website below:

http://www.gov.mb.ca/agriculture/news/insect/index.html

 

FLEA BEETLE FEEDING ACTIVITY INCREASING IN CANOLA

Flea beetle feeding injury increased this past week with the warmer weather. In seed treatment company trials, the untreated checks are above economic threshold levels (25% defoliation). Prosper 400 (Bayer CropScience) and Helix xtra (Syngenta Crop Protection) seed treatment had significantly lower injury rating at the research extension centers located in Carrington and Minot.

Some differences in control is being observed in the field based on variety and seed treatment. Injury ratings and yield from 2005 seed treatment company trials located in Carrington, Minot, and Langdon indicated that both seed treatments provided good protection against flea beetles feeding injury and higher yield than the untreated check.

Treatment

Minot
30 DAPa
Injury Ratingb

Minot
Yield lb/acre

Carrington
30 DAPa
Injury Ratingb

Carrington
Yield lb/acre

Langdon
30 DAPa
Injury Ratingb

Langdon
Yield lb/acre

Untreated check

4.0

1493

2.1

2023

2.5

2514

Helix lite

2.0

1802

1.1

2073

1.6

2623

Prosper 400

1.6

1769

1.1

2090

1.1

2632

Helix Xtra

1.5

1817

1.3

2012

1.1

2773

LSD (P=0.05)

0.7

252

0.6

NS

0.6

NS

a DAP = Days After Planting
b Injury Rating: 1= 0-3 pits per seedling, 2= 4-9 pits per seedlings; 3= 10-15 pits per seedling; 4= 16-25 pits per seedling; 5= >25 pits per seedling; and 6= dead seedling.

 

ADULT GRASSHOPPERS ALREADY?

Adult grasshoppers present in field now are rangeland species of grasshoppers and not the species of cropland grasshoppers which attack our agricultural crops. Some of the rangeland grasshoppers overwinters as late maturing nymphs and are ready to molt into adults as soon as temperatures warm up in spring. Examples of these rangeland grasshoppers are the Velvet-striped grasshopper (Eritettix simplex (Scudder)), speckled-winged grasshopper (Arphia conspera Scudder), green-striped grasshopper (Chortophaga viridifasciata (DeGreer)). Rangeland grasshoppers feed primarily on grasses of the rangeland and not crops. Cropland grasshoppers overwinter as eggs and are just starting to emerge as tiny young nymphs about the size of a wheat kernel. A grasshopper website for North Dakota can be found at:   http://www.ndsu.nodak.edu/entomology/hopper/orthoptera_home.htm

Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu

 

START LOOKING FOR ALFALFA WEEVILS

Alfalfa weevils overwinter as adults in plant debris, woodlots, and ditches. As temperatures warms up adult migrate to alfalfa field to lay eggs. By using degree days with a base of 48 , the life stages of alfalfa weevil can be predicted (see degree day table). Go to the insect section in the NDAWN website, http://ndawn.ndsu.nodak.edu/insectdd-form.html

and select the degree day base of 48F to determine the accumulated degree days for your location. See map of North Dakota for alfalfa weevil degree day accumulations.

Alfalfa Weevil map

Stage of Development

Degree Days Required to Complete Indicate
Life Stage

Accumulated
Degree Days
(base 48 )

egg

300

300

1st instar

71

371

2nd instar

67

438

3rd instar

66

504

4th instar

91

595

pupae

219

814

Scout fields by sampling 10 plants in 5 random locations (50 total plants) and walking in a M-shaped or similar pattern throughout the field. Small alfalfa weevil larvae are slate-colored. As larvae mature, their color changes to bright green with a white line running down their back and a black head capsule, and about th of an inch (see photo).

Alfalfa weevil
Source: Clemson University - USDA Cooperative
Extension Slide Series, www.insectimages.org

Management of weevil infested alfalfa stands depends on when the infestation occurs. If the infestation occurs relatively late, when the alfalfa has reached 20 to 25 inches in height, consider taking an early harvest. Small alfalfa weevil, those less than ¼ inch in length, will drop to the soil and generally die if the soil is dry. If the infestation occurs early, when alfalfa is 10 to 15 inches in height, chemical treatment may be necessary. Insecticide treatment is recommended if two live larvae per stem occur at this stage and 35 to 40% of the plants are showing tip feeding. In general, if alfalfa is 7-10 days out from harvest and 35-40% tip feeding is present, use an insecticide treatment. North Dakota insecticide recommendations for alfalfa are listed at the following website:

http://www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/ICG_06/05a_ForageCropInsects06.pdf

Remember to check the preharvest interval as these restrictions vary according to the insecticide used and the rate applied. Other factors to consider when selecting an insecticide is its price, potential hazards to honey bees and whether or not it is a restricted use insecticide.

If weevils infest an alfalfa field, be sure to scout the field following harvest for re-infestation of the second harvest. Major feeding by the alfalfa weevil will occur from 430 to 595 growing degree days (2nd - 4th instar). At greater than 600 growing degree days feeding normally stops and adult emerge. This will occur usually during the second harvest unless the first is taken late. If the following the first harvest, your scouting show 8 or more larvae per square foot or larvae are suppressing regrowth, chemical treatment is recommended.

Dwain Meyer
NDSU Plant Sciences
dwain.meyer@ndsu.edu

Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu

 

CUTWORMS IN SUGARBEETS

There have been reports of cutworms in sugarbeet in Moorhead, Crookston, Hillsboro and MinnDak. This is the expected timing for Red-Backed and Dark-Sided cutworms in beets; both occur in the Red River Valley and they have similar life cycles. They both over-winter as eggs laid by the adult moths in cultivated fields at the end of summer. The following late May/early June, the eggs hatch and the caterpillars move onto seedling crops.

Scouting – Early detection is important with this insect. Cutworms feed mostly in the evening and at night and so are sometimes difficult to locate in the daytime. Their feeding, usually at or below ground level, causes wilting, death and sugarbeet seedlings are often cut off near ground level. Scouting for these worrisome worms is best done by looking for wilting or dying plants and then looking in the top 1"-2" of soil at the base of these plants.

Thresholds & Treatment – An economic return on treatment can be expected when 4% - 5% of beets seedlings are cut in a field. Pesticides are best applied in the evening as this results in high levels of insecticide being present during the cutworms’ period of greatest activity. High humidity, dew and light rains (mist) can carry the insecticide over the plant surfaces and into the soil to increase contact with the insect. For the same reason, liquid formulations tend to be more effective against cutworms. To assist in delivering the insecticide to the caterpillars, break up severe soil crusting prior to, or during application.

For more information, go to the Red River IPM site at:  http://www.nwes.umn.edu/ent/redent.html

Ian MacRae
Dept. of Entomology; University of Minnesota
NW Research & Outreach Center; Crookston, MN
imacrae@umn.edu

For more information about cutworms, please see the article in issue 1 (May 6, 2006) of the Crop & Pest Report.


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