Variegated Cutworms Delaying Alfalfa Regrowth

       
                                             (Click on thumbnail for a bigger picture)

Variegated cutworms are still active on alfalfa with the commonly reported injury
being  delayed regrowth of the second crop.

The economic threshold is expressed on the number of days of delayed regrowth
that could be tolerated.  This threshold is the same for any other insects that may
cause delayed regrowth in alfalfa such as the alfalfa weevil.  The thresholds vary
with the cutting schedule of the grower, cost of treatment, and the market value
of the alfalfa on the field.

A thorough discussion and examples can be found in my Web site on the alfalfa
weevils under the "There is no regrowth! How long can I wait?" section at:

http://plantsci.sdstate.edu/ent/entpubs/awvl_EIL.htm

The insecticide list includes Baythroid, Lorsban, Pounce, Sevin XLR Plus, and
Warrior.  Read and follow label directions.

Thistle Caterpillars Transforming Into Chrysalis
(Second Brood Larvae Already Feeding?)

         
                                                                                         (NDSU)                       On soybean

To get a handle on when thistle caterpillars may start pupating, I kept a 1-inch-long thistle caterpillar
in my office and fed it with Canada thistle leaves for several days.  It was an inch long on June 12
then stopped feeding and metamorphosed into a chrysalis after 3 days on June 15. My room temperature
has been in the mid-70's.

The chrysalis of the thistle caterpillar can be seen suspended upside down in the picture above.
In nature, painted lady pupae can be seen suspended on the underside of thistle leaves.

This simplistic experiment indicates that the voracious caterpillar will eventually stop feeding,
and that inch-long caterpillars are within a few days of pupating. Spraying may not be recommended
if all of the caterpillars are an inch or more in length.

However, I did receive reports from several individuals that quarter-inch caterpillars can now be
seen on soybeans and sunflowers in Aberdeen (Gary Erickson, Ag. Educator), Selby (Kari Salvorson,
Crop Consultant), and Tripp County (Marty Phillips, Crop Consultant).  And that numerous painted
lady butterflies can now be seen flying in Brown County (Hamp Keahey, Crop Consultant). 

I am therefore of the opinion that the second brood caterpillars (born on the fields of SD) have already
starting to feed on crops and weeds.  Sunflowers, soybeans, and even corn need to be scouted
for defoliations.

Pounce, Warrior, and Sevin XLR Plus are labeled for use against thistle caterpillars on soybeans, while
Warrior is labeled for use against thistle caterpillars on sunflowers.

Black Cutworms Still Damaging Corn Near Arlington 

I inspected a cornfield near Arlington yesterday (June 18) with an economic infestation of black
cutworms.  The larvae were still actively feeding on the V4 seedlings and ranged in length from
a quarter inch to over an inch.

I did not expect black cutworms to have extended their range north to Brookings this year
and the fact that they are still quite active at this time.

All cornfields especially those to the north of I-90 must still be scouted for black cutworm activity.

Insecticide treatment may be considered if 5% (1 in 20 seedlings)
of the seedlings show signs of cutting or leaf feeding and the larvae
still less than an inch long.

Insecticides labeled for use on corn to control cutworms include
Ambush 2E, Asana XL, Lorsban 4E, Pounce 3.2EC and Warrior.
Read and follow all directions on the label.

Web posted on June 19, 2001 by Mike Catangui

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