NDSU Crop and Pest Report

Entomology


ISSUE 14  July 31, 2003

GRASSHOPPER ADULTS ON THE MOVE

With the widespread ripening of small grains and harvest beginning in southern counties, it is time to expect migration of grasshoppers to greener areas. The oldest adult grasshoppers have been moving for several weeks, more will be joining them over the next month. Monitor all late season crops for grasshoppers. Early detection may provide an opportunity to treat field margins, rather than having to treat entire fields.

Flax growers, remember you have Mustang Max available for grasshopper control under a Section 18 Emergency Exemption label.

Grasshopper activity map
Areas where grasshopper activity
continues to be high according to the
NDSU Pest Survey

 

WARRIOR WITH ZEON TECHNOLOGY: SPECIAL LOCAL NEEDS LABEL, 24(C), for Grasshoppers in Non-Cropland adjacent to Croplands

Syngenta has issued an SLN label for the use of Warrior in non-cropland sites adjacent to cropland for controlling grasshoppers. The non-cropland sites are described as right-of-ways, barrier strips, and fence rows. This label amends some an earlier SLN label to make use patterns consistent. An earlier SLN limited use to non-cropland sites adjacent to crops where Warrior was approved for use.

There is still a restriction on haying and grazing these non-cropland sites that are treated with this insecticide.

 

SUNFLOWER INSECT UPDATE:  Banded Moth, Sunflower Midge, and Seed Weevil

Banded moth are beginning their movement into fields. Last week the moths were sitting on vegetation in the field margins; numbers of moths in those sites this week were significantly less. Many people around the region have reported seeing large numbers of moths, also. The close observers are reporting large numbers of eggs on the bracts, as well.

Reports from Dr. Gary Brewer indicate that there are some Sunflower Midge infested fields beginning to show up around the region. Unfortunately, there is no insecticide response that has proven successful to control midge larvae. Fields where he reported some significant injury were located in the Perley, Minnesota area. Fields on both sides of the river were affected at some level. The scarring of bracts and the stalk at the base of leaf petioles are the visible symptoms at this time. Midge larvae are still present on many of the plants but will be dropping down to the soil soon. Dr. Brewer has also indicated that their surveys are finding some midge eggs still on buds in some of the more severely infested fields.

Red Seed Weevil are also on the move. Dr. Brewer’s research group reported finding seed weevil moving into wild sunflower last week, and are now seeing large numbers of weevils moving into commercial fields. Last year’s National Sunflower Association regional survey detected significant seed injury from weevils throughout the southern counties of North Dakota and in central counties of South Dakota. Scouting seed weevil in confection and oilseed fields will be critical this season.

Seed Weevil damage map
Enclosed areas had Seed Weevil
damaged seed at a level greater
than 6% in 2002.

Red Seed Weevil Management in Oilseeds

To decide whether to use an insecticide treatment to control red sunflower seed weevils, it is necessary to determine the economic threshold your situation this year. The economic threshold (ET) for red sunflower seed weevil depends on the following variables:

  • the cost of insecticide treatment per acre
  • the market price of sunflower in $ per pound
  • the plant population per acre
  • ET =                          Cost of Insecticide Treatment                       
                  Market Price x 21.5 ((0.000022 x Plant Pop/n) + 0.18)

    Red Seed Weevil Economic Thresholds (Weevils per head)

    Plant population = 18,000 per acre

    Market Price ($)

    Treatment Cost ($/A)

    6.00

    7.00

    8.00

    9.00

    10.00

    11.00

    0.07

    7

    8

    9

    10

    12

    13

    0.08

    6

    7

    8

    9

    10

    11

    0.09

    5

    6

    7

    8

    9

    10

    0.10

    5

    6

    6

    7

    8

    9

    0.11

    4

    5

    6

    7

    7

    8

    0.12

    4

    5

    5

    6

    7

    7

    0.13

    4

    4

    5

    6

    6

    7

    Price for Oilseed Sunflowers = $0.09

    Plant Population

    Treatment Cost ($)

    6.00

    7.00

    8.00

    9.00

    10.00

    11.00

    17,000

    6

    7

    7

    8

    9

    10

    18,000

    5

    6

    7

    8

    9

    10

    19,000

    5

    6

    7

    8

    9

    10

    20,000

    6

    7

    8

    8

    8

    9

    21,000

    5

    6

    6

    7

    8

    9

    22,000

    5

    5

    6

    7

    8

    9

    23,000

    5

    5

    6

    7

    8

    9

    24,000

    4

    5

    6

    7

    7

    8

    25,000

    4

    5

    6

    6

    7

    8

    Sunflower plant stage is used to time insecticide treatments. For oilseeds, the ideal plant stage to treat is when most plants in the field are at 40 percent pollen shed. However, we recommend that treatment be considered when more than half of the plants in the field are just beginning to show yellow ray petals to 30 percent of the heads shedding pollen and the rest of the plants in the field are still in the bud stage. The consideration of treatment at the early bloom stage should allow growers a sufficient cushion of time to have their fields treated. Growers must be aware, however, that if weevil populations are high and/or spraying is done too early, a reinfestation may occur and a second insecticide application may be necessary.

    Insecticides registered for seed weevil control inlcude Asana, Baythroid, Lorsban, Methyl parathion, 6-3 parathion_methyl parathion, Scout X-TRA, Warrior.

    Confection or Hulling Market

    The banded moth, seed weevil, and the Lygus bug have all impacted quality of these sunflowers the past four seasons. It is recommended at this time, that sunflowers grown for these markets be treated a minimum of two times, once at early flowering and again 5 to 7 days later. With this type of program, a window of protection should be provided to minimize impact from all three of these seed damaging insect pests.

    Growers should be planning now for treatment schedules. When flowers begin blooming across the region, competition for access to aerial applicators increases.

    Reducing Insecticide Rates or Volumes ?

    Insecticide labels have recommended rates and volumes that users should follow. The rates are based on trials and have been set to provide consistent results over a range of environmental conditions. For many of our sunflower head feeding insects, the best field results have often been obtained with mid to upper rate ranges. In light of some of the large populations being reported early, selection of the higher rates may be even more critical this year.

    Volume is also important. When reducing the total volume of spray per acre there is the risk of reducing the effective coverage of our treatment target. If the droplet coverage on the plant surface is reduced, there is less chance of contacting an insect during the application and with droplets leaving residual for insects to contact later. Reduced volume further risks evaporation of the spray under hot dry conditions, limiting the amount of product that ever reaches the target.

     

    SOYBEAN APHID UPDATE

    Soybean aphid numbers continue to creep upwards. There were some reports of significant numbers of aphids in the central part of the Red River Valley (near Hillsboro) that required treating. The field descriptions of these sites indicated they were smaller fields with wooded areas (shelterbelts or waterways) on multiple sides of the field.

    Soybean aphid map
    Location of fields with greatest
    numbers of Soybean Aphid
    according to NDSU Pest Survey.

    NDSU surveys have yet to find fields that have reached treatable levels. In general, aphid colonies have greater numbers than last week, but still below the 25 aphids per leaflet or a total of 200+ aphids per plant. Aphids can be found in most fields in the southeast counties where our survey efforts have been concentrated. Greatest numbers of aphids are still near protected areas along shelterbelts. Winged aphids are being found on field edges. Many of the winged aphids are being found with one or two small aphids nearby.

    Phillip Glogoza
    Extension Entomologist
    pglogoza@ndsuext.nodak.edu

     

    POTATO INSECT ALERT: Potato insect update for the Northern Great Plains, week ending July 25

    (source: Edward B. Radcliffe, Department of Entomology, University of Minnesota)

    Aphid flight activity across the Northern Great Plains increased considerably during the past week. The most abundantly represented species were bird cherry-oat aphid, buckthorn aphid, and turnip aphid. The trap data did not show increases in green peach aphid activity, but colonization of potato by this species is now occurring. Growers are advised to scout their fields, paying particular attention to field margins adjoining fallow, e.g., headlands or planting skips.

    This summer participating Minnesota and North Dakota potato growers have entered 30 potato fields in a large-scale University of Minnesota demonstration/research project. The project's objective is to evaluate possible benefits of targeting the year's first insecticide [Monitor (methamidophos)] spray treatment for green peach aphid along field margins. The first 6 fields were sprayed today. Twenty four more are scheduled to be sprayed next week. We have previously shown that initial colonization of potato fields by green peach aphids occurs almost exclusively along field margins that are kept fallow. For the first 10-14 days following initial invasion of a potato field by winged green peach aphid, more than 90% of colonizing green peach aphids are found within the first 10-20 yards from a fallow border.

    This colonizing behavior of green peach aphid provides growers the opportunity to target insecticide applications on those portions of the field where treatment will be most advantageous. In preliminary studies, potato growers were able to reduce their use of Monitor by 80% by treating only crop margins. The advantages of using targeted insecticide applications include effective aphid control at less cost, conservation of natural enemies in the untreated center of the field, and reduced selection for insecticide resistance. Monitor resistant green peach aphids have been reported from some fields in the Pacific Northwest.

    Note: the Aphid Alert information reported in these weekly newsletters can be obtained earlier by accessing the information from the website or subscribing to the weekly e-mail update. The web address is:

    http://ipmworld.umn.edu/alert.htm

     


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