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ISSUE 8   June 28, 2007

POTATO LEAFHOPPER PROBLEMS CONTINUE

High populations of potato leafhopper have occurred in newly seeded and 2nd growth seedling alfalfa, and dry bean fields with some fields being treated with insecticide. Problems with potato leafhopper in 2nd growth seeding alfalfa is not typical in North Dakota. However, Dr. Dwain Meyer said that this is only the second time in his 38 years that he has observed leafhopper causing damage in 2nd regrowth seedling alfalfa. Potato leafhopper treatments need to be preventative rather than curative. If significant infestions occur, leafhoppers will literally stop the growth of the seedlings with hopperburn, V-shaped yellowing of the leaf tip. Once the yellowing tips called "hopper burn" is apparent throughout the field, damage is already done and treatment is not recommended. Scout for increasing leafhopper populations.

Economic thresholds in alfalfa are:

Alfalfa Height (inches)

Potato Leafhoppers per sweep

<3 inches

0.2

3 to 6 inches

0.5

7 to 11 inches

1.0

12 inches or taller

2.0

 

BEGIN SCOUTING FOR SOYBEAN APHIDS IN NORTH DAKOTA

Low numbers of soybean aphid (see photo) have been observed in the southeastern part (Cass, Sargent Counties) of North Dakota last week. Average numbers of aphids are very low, about <5 aphids per plant. Crop stages of soybeans are still in the early vegetative stages (V1 to V3) crop stages. The Multicolored Asian lady beetle (Harmonia axyridis), a predator of soybean aphids, was also observed in soybean fields.

Soybean aphid
Soybean aphid (photo by D. Ragsdale, Univ. of MN)

Time to start scouting fields. Aphids are found on the underside of leaves in the upper canopy early in season. Check several location per field. The critical growth stage for making soybean aphid treatment decisions is in the late vegetative to reproductive (Vn to R5). Assessing aphid populations during early reproductive stages are critical for optimal yield. The following economic thresholds based on crop growth stages are:

  • R1(beginning flower) to R5 (beginning seed) = 250 aphids/plant when populations are actively increasing
  • R6 (full seed) = No treatment necessary. Research trials throughout the north central states have not demonstrated a yield benefit to treating soybean for soybean aphid management at the R6 and beyond stages.
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    NORTHEAST REGION OF NORTH DAKOTA AT HIGH RISK FOR WHEAT MIDGE INFESTATION

    A soil survey conducted last year detected increasing levels of overwintering wheat midge larvae for the 2007 season (see map). Wheat midge populations ranged from zero to 1,250 midge larvae per square meter, with most of the state having less than 200 midge larvae per square meter during 2006. However, two "hot" spots with more than 500 midge larvae per square meter have shown up in Cavalier and Towner counties in northeastern North Dakota. Fields with more than 1,200 midge larvae per square meter are considered high risk. At that point, some control tactic must be used to reduce midge populations or planting of a non-wheat host, such as canola or sunflowers, is recommended. There also are several pockets of lower numbers of 201 to 500 midge larvae per square meter in northern Ward County and north-central Mountrail County. It is always a good idea to scout areas with more than 200 midge larvae per square meter and determine if economic population levels exist in wheat/durum fields in the susceptible crop stage – heading to early flowering.

    Wheat Midge Larval Survey map

    A degree day (DD) model using daily temperatures to calculate DD accumulations allows for a more accurate prediction of local adult emergence. Observations indicate the following DD accumulations for events in the midge population (degree day base = 40 F).

    DD

    Biological Event

    450

    The midge breaks the larval cocoon and moves close to soil surface to form the pupal cocoon.

    1300

    10% of the females will have emerged.

    1475

    About 50% of the females will have emerged.

    1600

    About 90% of the females will have emerged.

    Wheat midge degree days are moving along fast with the above average heat units with this past week’s temperatures in the 90s! Most of the northern tier of North Dakota is near 1300 and the southern tier near 1600 DD (see DD map).

    Midge growing degree day map

    Environmental conditions play an important role in wheat midge development and activity. With the adequate soil moisture, warm temperatures, and high humidity, wheat midge emergence and flight conditions are favorable to economic infestations. Soil conditions in reduced tillage situations will vary from normal tillage conditions and may delay some midge emergence in a region. Conditions that favor survival of adult midge may put even later planted wheat at some risk. The highest wheat midge populations can be found in fields where wheat on wheat was grown in previous years.

    Scouting until adult midge activity has reached well below economic levels is the best way to avoid unnecessary losses due to wheat midge infestations. Monitoring for adult midge (see photo) should be conducted at night (after 9:00 PM), warm night temperatures >60 degrees F, and light winds <6 mph. Economic thresholds are:

  • Hard Red Spring Wheat = one wheat midge per 4-5 heads
  • Durum = one wheat midge per 7-8 heads.
  • Wheat midge on crop

    Typically, the most significant flight period for the entire wheat midge population extends over a 14 to 18 day window of time within a region. Individual adult midge may survive from 3 to 7 days, depending on favorable conditions (warm, calm, humid weather). Although adult wheat midge are not strong flyers, recent field reports suggest that wheat midge can be blown several miles on the wind aiding dispersion. Remember to wear your mosquito protection!

    DIAMONDBACK MOTH LARVAE IN CANOLA

    Some canola fields located in the north central region of North Dakota and in Manitoba were sprayed for diamondback moths (source: D. Markle, J. Gavloski). Pheromone trap catches have been unusually low for high numbers of adults being observed in field. Possible reasons include poor trap placement, ineffective pheromone lures, ...It’s always good insurance to monitor canola fields for larvae of diamondback moth from bloom to early pod. Beat plants into a white bucket to dislodge larvae from plants. After beating plants, count larvae on ground or dangling from plants on a silk thread. Again, check several locations per field. The action threshold for diamondback moth larvae in canola at the pod stage is about 20 per square foot (or two to three larvae per plant). For the early flowering stage, insecticide applications are likely required at larval densities of 10-15 larvae per square foot (one to two larvae per plant). Early monitoring of adults and larvae are critical for preventing losses, especially in flowering canola where larval feeding cause flowers to abort.

    PROTECT OUR VALUABLE HONEY BEES - NATIONAL POLLINATOR WEEK

    Honey bees are important to agriculture worldwide, serving as pollinators for many crops. In fact, every third bite of food that we take is attributed to a bee-pollinated flower or nut. To focus attention on the importance of pollination, the U.S. Senate and U.S. Department of Agriculture have designated June 24-30 as National Pollinator Week.

    Honey bee

    Honey bee pollination increases yield and quality of crops. Honey bees also pollinate wild flowers in natural ecosystems and plants in home gardens. The monetary value of honey bees as commercial pollinators in the U.S. is estimated at $15 billion annually.

    Honey bees are important in honey production, too. North Dakota leads the nation in production for the third consecutive year. It produces 17 percent of the nation’s total. North Dakota’s share of honey production is valued at more than $27.3 million.

    However, the number of honey bees has been declining throughout the world. The U.S. has lost more than 50 percent of its managed honey bee colonies in the last 10 years, according to the North American Pollinator Protection Campaign. Reduced pollination could affect major crops grown in North Dakota, including sunflowers, soybeans, canola and alfalfa.

    Honey bee losses have occurred in the past, but current losses are different. For example, honey bees are failing to return to the hive, which is uncharacteristic, and bee colony losses are rapid and occur in large numbers. This is a condition known as colony collapse disorder (CCD). In North Dakota, losses have been as high as 50 percent. Between 50 percent and 90 percent of the beekeepers reporting losses are large, commercial, migratory beekeepers.

    The true reason behind colony collapse disorder still is a mystery. Scientists who are researching this phenomenon have suggested the following reasons:

  • Parasites, mites and diseases in the bees and broods
  • Pathogens and immunodeficiency
  • Poor nutrition or malnutrition among adult bees
  • Stress on honey bees from transportation, confinement and environmental conditions
  • Pesticides used to control parasites in bee hives
  • Pesticides used to control pests in agricultural crops and other situations, which cause chemical residue/contamination in the wax, food stores and bees. The new class of insecticides known as neonicotinoids is being targeted because the insecticides, applied as seed treatments, can move through the plant systemically and later may be incorporated into the pollen and nectar.
  • Lack of genetic diversity and lineage of bees
  • A combination of factors
  • The last point seems to be what many scientists agree on - that a number of factors may be causing CCD.

    To help protect honey bees, ag producers and home gardeners can reduce pesticide use and spray only when necessary. For example, producers have established economic thresholds for many agricultural pests to help make proper treatment decisions only when necessary.

    Producers who use pesticides on blooming crops should select one with low toxicity to bees when possible and time pesticide application preferably for late evening to avoid bees’ peak foraging periods. Producers also should be aware of potential spray drift onto blooming crops or weeds that honey bee may be visiting and protect water sources close to bee hives from pesticide contamination. Plus, planting flowers for honey bees and other native pollinators will help ensure sustainable crop pollination.

    Janet Knodel
    Extension Entomologist
    Janet.Knodel@ndsu.edu


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