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ISSUE #11  July 12, 2001

 

THISTLE CATERPILLAR UPDATE

Caterpillars are growing rapidly. The majority of the caterpillars feeding on soybeans and sunflowers are reaching the 1 1/4 inch size. The chrysalis, or pupa, should be a common site at the end of this week and next week. The Painted lady butterfly should be out in the next two weeks.

There are still a few reports of thistle caterpillars feeding in canola. The next generation is more likely to be found on sunflower than other crops. The Painted lady butterfly prefers nectar from composites 3_6 feet high, especially thistles, also aster, cosmos, blazing star, ironweed, and joe-pye weed. Flowers from other families that are visited include red clover, buttonbush, privet, and milkweeds.

As sunflower and soybean plants become larger, greater numbers of caterpillars will be required to approach the 20% defoliation levels.

 

WHEAT MIDGE UPDATE

Reports of significant activity have only come from northwest quarter of the state, particularly northwest McLean County. In that area, midge have exceeded the treatment threshold and insecticide has been applied. Other areas are reporting the ability to detect midge with sweep nets, sweeping paper plates through wheat heads, sticky traps, etc. However, the head counts are below thresholds.

Degree day accumulations have reached or exceeded 1600 DD in all areas of the state except the northern most counties (Cavalier to Burke counties). Emergence is nearly complete at 1600 DD, but adult midge remain active and pose a risk up to about 1800 DD. Continue to scout heading wheat for another week to be sure of infestation potential.

The following is the summary of activity reported by Jan Knodel, Plant Protection Specialist-Minot.

Wheat Midge Night Scouting Reports from North-Central, ND

Areas with HIGH wheat midge pressures - HOT!

Areas with MODERATE pressures and limited spraying:

Areas with LOW pressures:

The following table illustrates the benefits of properly timed spray applications for wheat midge and scab control. The 50% flowering spray timing resulted in a lower yield increase than the spray timings at 25% flowering and late heading for both wheat midge and scab management. The wheat midge and scab pressures were high at this site last year.

Results of 2000 Wheat Midge-Scab Timing Study on HRSW Cultivar Amidon at Noonan, Divide County
(J. Knodel and K. Brown).

Treatment
Formulation

Rate
Fl. oz/A

Crop Stage

% Kernels Infested

Ave. Yield
bu/A

Yield Increase
bu/A

% Gain

Untreated

   

8

18

0

--

Lorsban 4E-SG

16

Late heading

2

25

7

42

Lorsban 4E-SG +
Folicur 3.6F +
Induce 0.6% V/V

16
4

Late heading

4

33

15

85

Folicur 3.6F
Induce 0.6% V/V

4

Late heading

9

29

11

63

Lorsban 4E-SG

16

25% flowering

4

27

9

51

Lorsban 4E-SG +
Folicur 3.6F +
Induce 0.6% V/V

16
4

25% flowering

4

38

20

113

Folicur 3.6F
Induce 0.6% V/V

4

25% flowering

5

31

13

74

Lorsban 4E-SG

16

50% flowering

2

22

4

22

Lorsban 4E-SG +
Folicur 3.6F +
Induce 0.6% V/V

16
4

50% flowering

3

23

5

31

Folicur 3.6F
Induce 0.6% V/V

4

50% flowering

8

27

9

50

Insecticide Application and Rates:

Janet J. Knodel
Area Extension Specialist Crop Protection
North Central Research and Extension Center

 

CONFECTION SUNFLOWER AND KERNEL BROWN SPOT

brown_spot.jpg (143862 bytes)

Concerns have been raised during the past three seasons about a damage to confection sunflower seeds. The damage has been named kernel brown spot because of the dark spot that is present. All evidence to date suggests that the problem is due to feeding by Lygus on the developing seed.

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Lygus nymph Lygus adult

Lygus are most noted for being a pest in seed production of many crops. Their preference for food is meristematic tissue, embryonic tissue or new growth of any kind. Lygus insert their mouthparts into the host and start a "pre-digestion pump" to inject saliva and start digestion, then suck the fluid into the stomach. This is where the injury originates. The saliva is toxic to plant tissue, helping reduce the plant fluid into a digestible source. The result in sunflower seeds is the brown to black spot due to tissue death at that feeding site.

There is still much to learn about Lygus and sunflowers in the region. In the mean time, to minimize the damage which result in a quality reduction, a general approach to protecting sunflower from Lygus and other seed feeding insects is being recommended.

Sunflower is susceptible to Lygus damage during flowering, from anthesis through seed hardening. A number of insecticides labeled for controlling head feeding insects in sunflower are available. Of these, the Organophosphate (Lorsban, Methyl Parathion, Parathion) and pyrethroid (Asana XL, Baythroid, Scout X-Tra, Warrior) insecticides do control Lygus. One problem is that none of these products includes Lygus on the sunflower label. Lygus can be treated at the same time confection sunflower is treated for other insects, such as the seed weevil and banded sunflower moth.

Currently, NDSU Entomologists are suggesting two treatments are needed to sufficiently protect confection sunflower heads from insect feeding: One application at the onset of pollen shed or approximately 10% bloom, followed by a second treatment 7 days later. This program should adequately control insects on confection sunflower throughout flowering, minimizing the potential feeding damage.

 

UNIVOLTINE EUROPEAN CORN BORER EMERGENCE AT PEAK

The single-generation European corn borer are at 50% emergence in the east and south central areas of the state. Central counties will reach the peak around July 14. It is now time to monitor borer activity to determine when and if larval infestations exceed treatable levels. In the central valley, egg masses from corn borer could be found on plants, though they are still scarce.

There have been reports of larval infestations from the earlier emerging bivoltine corn borer (two generation). These reports have primarily been from the southeast corner of the state and south central counties along the Missouri River. Some people have commented that these infestations were concentrated near field margins. The corn borer moths will stage in grassy borders where they mate and females drink available water. Later, moths move into the field to lay eggs. In these cases, infestations near field margins are common.

Field scouting for corn borers:

Whorl stage corn . . . . Pull the whorls from 10 plants at 5 locations across the field. Select whorls at random, avoiding damaged plants. Unwrap the whorl leaves; count and record the number of live larvae found.

Use the corn borer worksheet to help make decisions about the profitability of treating an individual field.

Worksheet for Corn borer in whorl stage corn . . . You fill in the blanks

1. ___% of plants infested

x___ Avg no. borers/plant

=___ Borers per plant

2. ___borers per plant

x ___% yield loss per borer*

= ___percent yield loss

3. ___percent yield loss

x ___expected yield (bu/acre)

= ___bushels/a loss

4. ___bushel loss per acre

x ___price per bushel

= ___$ loss per acre

5. ___loss per acre

x ___percent control**

= ___$ preventable loss/a

6. ___preventable loss/acre

- ___cost of control per acre

= ___$ profit (loss)/acre

*5% for corn in the early whorl stage; 4% for late whorl; 6% for pretassel
**80% for granules; 70% for sprays.

Economic Threshold (Corn borer/plant) when factoring Crop Value and Control Costs

Control Costs2 ($/acre)

Value of Corn Crop1 ($/acre)

200

250

300

350

400

450

500

550

600

6

0.75

0.60

0.50

0.43

0.38

0.34

0.30

0.27

0.25

7

0.88

0.70

0.58

0.50

0.44

0.39

0.35

0.32

0.29

8

1.00

0.80

0.67

0.57

0.50

0.45

0.40

0.37

0.34

9

1.12

0.90

0.75

0.64

0.56

0.50

0.45

0.41

0.38

10

1.25

1.00

0.83

0.71

0.63

0.56

0.50

0.46

0.42

11

1.38

1.10

0.92

0.79

0.69

0.61

0.55

0.50

0.46

12

1.50

1.20

1.00

0.86

0.75

0.67

0.60

0.55

0.50

13

1.63

1.30

1.08

0.93

0.81

0.72

0.65

0.59

0.54

14

1.75

1.40

1.17

1.00

0.88

0.78

0.70

0.64

0.59

15

1.88

1.50

1.25

1.07

0.94

0.84

0.75

0.68

0.63

16

2.00

1.60

1.33

1.14

1.00

0.89

0.80

0.73

0.68

1 Crop value = expected yield (bu/acre) X projected price ($/bu)
2 Control costs = insecticide price ($/acre) + application costs ($/acre)

Phillip Glogoza
Extension Entomologist
pglogoza@ndsuext.nodak.edu


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