Palestriped Flea Beetles On Sunflower Seedlings

  

The palestriped flea beetle (Scientific name: Systena blanda) caused severe stand losses in
sunflower seedlings in seven central SD counties.  Reports of  damaging numbers of the flea
beetle came from Hughes, Sully, Walworth, Faulk, Hyde, Potter, and Tripp counties.
Damages appeared to have been confined to these central SD counties close to the river.
The flea beetles chewed numerous holes on the leaves and cotyledons of the seedlings
causing the seedlings to wilt and die.  Sunflowers were less affected once they made it
through the seedling stage.

Palestriped flea beetles are not normally a pest of sunflowers.  Thus, no economic thresholds
or labeled chemicals are currently available to recommend to sunflower growers.  The
palestriped flea beetle is a known pest of carrot and tomato in California and North Carolina,
respectively.  It is also known to feed on numerous plants including potato, grapes, beans,
strawberry, and corn.

Records show that the palestriped flea beetle has a widespread presence both in South
Dakota and the entire United States.  Adults are about 3/16 of an inch long, black, with 2
longitudinal stripes on the back (click on the thumbnail above).  Like any flea beetle species,
the palestriped flea beetle has enlarged hind legs enabling them to jump from plant to plant.

Adults overwinter on the field under the soil and plant debris.  They then resume feeding in
the spring of the following year.  These overwintered beetles will then lay eggs in the soil
near the base of host plants.  Grubs feed on plant roots then transform into pupae, then
adult flea beetles in the summer.  There is only one generation per year.

    Russian Wheat Aphids Found Near Scenic, SD

Russian wheat aphids (Scientific name: Diuraphis noxia) are a consistent pest of wheat and barley
in southeastern Colorado and western Nebraska.  In South Dakota, their damage had been light
and sporadic.  Russian wheat aphids may be mainly an arid land pest of wheat and barley.
They do not infest corn, sorghum, or proso millet, and do not transmit any wheat diseases.

The main distinguishing feature of the Russian wheat aphid is the presence of a "double-tail"
or "forked-tail" on the tip of its abdomen when viewed from the side.  Click on the picture above
to see this structure.  No other aphid in SD field has this feature.  A magnifying lens or microscope
must be used since the aphid is only about 1/10 inch long or less.  A map of SD indicating where
Russian wheat aphids had been found in the past is included above.

Last week, Clair Stymiest (SDSU Extension Agronomist, West River Ag. Center) detected the
Russian wheat aphids on dough stage spring wheat near Scenic, SD.  At this time, insecticidal
treatments may not be beneficial.  Also, most labeled insecticides have very long pre-harvest
intervals. Di-Syston 8 (0.7-1 pint per acre), Dimethoate 4E (0.75 pint per acre), Lorsban 4E-SG
(0.5-1 pint per acre), and Warrior T (2.56-3.84 fluid ounces per acre) have preharvest intervals of 30,
35, 28, and 30 days, respectively.

Our main concern now is the next crop of winter wheat that will be planted in the fall.  Areas where
the Russian wheat aphid may be present should plant winter wheat as late as possible.  Late
planting will also alleviate injuries due to greenbugs and bird cherry oat aphids (and the diseases
they transmit) and grasshoppers.

For excellent information on the biology and control of Russian wheat aphids kindly visit these sites:

        www.ianr.unl.edu/pubs/insects/g936.htm    (University of Nebraska)
        www.colostate.edu/Depts/IPM/ento/j568.html   (Colorado State University)

A formula for calculating economic thresholds can be found in the CSU site.  This takes into
account the cost of spraying, predicted yield, market value of wheat, and stage of plant development.

  Ray Gosmire Finds True Armyworm in Mitchell

A non-economic population of true armyworms was detected in Mitchell by Ray last week (7-5-00).
After Ray personally inspected the corn field, he indicated that no treatments would be necessary.
Ray sent the specimens above.  Notice the black stripe above each abdominal proleg of the larva.
This feature separates armyworms from other striped larvae that may be found on the field at this
time.

Although the numbers are not economic, it signals the potential presence of armyworms in some
fields.  Armyworms can be very damaging to small grains and corn if present in high numbers.
Economic thresholds in corn are 2 worms per plant on 25% of the stand, or 1 worm per plant on
75% of the stand.  On small grains, the threshold is 5 worms per square foot.  I have no idea who
created these thresholds but seem to be the only guidelines at the moment.

Infestations usually starts in grasses injured by hail and lodged to the ground.  Armyworm moths
migrate into the state from the south.  Fields with a lot of foxtails also appear to attract armyworm
moths.  Numerous chemicals are available for use against armyworm on corn.  Insecticides for use
on small grains have a lot of restrictions and so make sure you read and follow the fine prints on
the label.

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