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ISSUE 7   June 26, 2008

RECENT FIELD OBSERVATIONS OF INSECT PESTS

Potato - Colorado Potato Beetle: Adult Colorado potato beetles are emerging now from overwintering sites. The adult is 3/8 inch long, with oval body and a yellow-brown color with 5 black stripes on each wing cover (see photograph). Eggs are laid on the underside of leaves in clusters of 10 to 30 and are orange colored when ready to hatch (see photograph). The larvae are 1/8 to 3/8 inch long, brick red to light orange in color. Both adults and larvae feed on potato foliage.

The treatment recommendation is that spraying be initiated at first egg hatch. Best results have been achieved by flagging the first egg masses that can be located, monitoring these daily, and spraying at 15 to 30% hatch.

Adult colorado potato beetle
Colorado Potato Beetle - adult

Colorado potato beetle eggs
Colorado Potato Beetle - eggs

Soybean - Soybean Aphid: Very low number of soybean aphids have been found in soybeans growing the Red River Valley region of North Dakota and Minnesota and other areas of Minnesota (Crookston, Lamberton, Rosemont, Becker, Morris). The current temperatures between 77 and 86 F are optimal for soybean aphid development. The pre-reproduction period takes about 5 to7 days before aphids begin birthing little nymphs. When scouting soybean field, remember the many different insects inhabit soybean fields throughout the season. Be sure to properly identify aphids and any look-alike insects - thrips, insidious flower bugs, spider mites, leafhoppers, and so on. A good reference is the Identification of Soybean Aphid and Look-alike Species, published by the North Central IPM Center.

http://www.ncipmc.org/alerts/soybeanaphid_id.pdf

Itís important to be aware of aphid predators, because they play a major role in reducing early population of soybean aphids. Research results have indicated that early-season application of insecticides for control of sub-economic populations of soybean aphids have caused more harm than good. So, no early-season insecticide applications are recommended for pest management of soybean aphids.

Soybean / Dry Bean - Bean Leaf Beetle: Bean leaf beetles have been increasing in North Dakota over the past years Adult bean leaf beetles are emerging from overwintering sites and moving into soybean or dry bean fields. The adults are yellow to reddish-brown and three to four black spots with a black border on wing covers (see photograph). Early feeding injury to leaves appears as small round holes between the leaf veins (see photograph). Treatment thresholds from other regions are 3 to 7 beetles per sweep or based on defoliation - 50% defoliation during early vegetative, 40% defoliation during pre-bloom, 35% defoliation during bloom and 20-25% defoliation during pod set to fill. Late season feeding on the foliage and pods by the new adults that emerge in August appears to be more important than early season feeding. This may increase the risk of virus transmission and cause secondary infections (rotting and discoloration) from fungi and bacteria.

Adult bean leaf beetle
Adult bean leaf beetle (photo by N. Wright, Fla.
Dept. of Ag. and Cons. Serv., Bugwood.org)

Bean leaf beetle feeding on soybean
Bean leaf beetle feeding on soybean
(photo by C. Strunk, SDSU, Bugwood.org)

Sunflower - Sunflower Beetle: Adult sunflower beetles (see photo.) are emerged, however, no economical populations have been reported. The economic threshold is 1 to 2 adults per seedling on seedlings. Please refer to the NDSU Bulletin E-824 for more information:

http://www.ag.ndsu.edu/pubs/plantsci/pests/e824.htm

Adult sunflower beetle
Adult sunflower beetle

Small Grains - Cereal Aphids: Low numbers of cereal aphids are being reported throughout the state (see IPM map). For scouting and economic threshold recommendations, please refer to issue 5 of the Crop & Pest Report on June 12, 2008.

Aphids map

Barley - Barley Thrips: Sampling for thrips should begin when the flag leaf is first visible and continue until the head is completely emerged from the boot. Most thrips can be found under the top two leaf sheaths. The dark brown to black thrips can be found by unrolling the leaf sheaths away from the stem. With the high market value of barley, the economic threshold is lower in 2008 than previous years. Using a cost of control of $8.00 per acre and dollar value per bushel of $6.50, the current threshold is only 3 thrips per stem. Insecticide treatments are only effective when applied before heading is complete.

 

AVOID FLAG LEAF APPLICATIONS OF INSECTICIDE FOR CONTROL OF WHEAT STEM MAGGOT

Preliminary research indicates that insecticides applied at the flag leaf stage were NOT as effective in reducing the number of white heads caused by wheat stem maggot when compared to insecticides applied at the 4-leaf crop stage (see table). Warrior insecticide reduced the number of white heads caused by the wheat stem maggot when applied at to 4-leaf wheat. However; the number of white heads per plot was not significantly different from the untreated plot when Warrior was applied later in the growing season. Wheat yield was the greatest where Warrior was applied with a fungicide (Quilt or Tilt) for leaf disease control at the 4-leaf stage. Although later season applications of fungicide also increased wheat yield, it did not show the same level of increase as the 4-leaf application applied with an insecticide (Warrior).

NDSU Ext. Entomology recommends ĎNOT to add an insecticideí at flag leaf for control of wheat stem maggots or when no economic levels of insect pests are present in field.

Treatment

Rate (fl oz/a)

Timing

White heads (plts/plot)

Leaf disease %

Yield (bu/a)

Test Weight(lb/bu)

Untreated

   

27

55

14

57.5

Warrior + Quilt

2.56 + 7

4-leaf

4

25

22

58.2

Warrior + Tilt

2.56 + 2

4-leaf

13

35

23

58.1

Warrior

2.56

Flag leaf

21

42

15

57.1

Warrior + Quilt

2.56 + 14

Flag leaf

26

22

16

58.5

Quilt

14

Flag leaf

25

14

18

58.1

Warrior

2.56

Early heading

22

61

17

57.3

LSD (0.05)

   

13

NS

3

0.6

CV

   

38

50

9

0.6

Clearfield HRSW was seeded May 24, 2007, at 1.1 million seeds/A. Source: D. Markle, NCREC, Minot, ND

 

STILL EARLY IN SEASON FOR COLLECTING LEAFY SPURGE FLEA BEETLES

There have been several questions about how many degree days are required for collecting leafy spurge flea beetles. The accumulated growing degree days (AGDD) for sunflower (base of 44 F) can be used as a guide to determine when to begin scouting for adult flea beetles. Begin scouting for adult flea beetles when the AGDD approaches 1,000. Likewise, the flea beetle population and egg laying by females begins to decline when the AGDD reaches 1,600 or more. Collect flea beetles between 1,200 and the 1,600 AGDD. 

With the cool spring temperatures, most of North Dakota is still below 1,000 AGDD (see sunflower AGDD map), except for the far southeastern region. The GDDs for sunflower are about 200 GDDs behind the five-year average. Use the sunflower degree days/growth stage application in NDAWN and enter "2008-03-01" for planting date and select "degree day" for map type.

http://ndawn.ndsu.nodak.edu/sunflowergdd-form.html

Sunflower GDD map

Janet J. Knodel
Extension Entomologist
janet.knodel@ndsu.edu


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