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ISSUE 4  MAY 27, 1999

MOTH FLIGHTS RAISE QUESTIONS IN SOUTHEAST ND

    Several questions have come from the southeastern counties about moths that are active in fields. There are several common moths that are appearing at this time of year. The two most common are not generally agricultural pests. Two others are potential pests.

    The one that is our greatest concern is the armyworm, Pseudaletia unipuncta. These moths have a coppery colored appearance. A small white dot is visible in the middle of each front wing.

Armyworm Moth

armywrm_moth.jpg (180456 bytes)

   In southern Minnesota, flights of black cutworm, Agrotis ipsilon, are underway. Typically for North Dakota, the numbers of black cutworm moths migrating into our area is minor. These moths are darker in color, a grey to charcoal, compared to the armyworm. They lack the white dot. Instead, they have a black wedge or dagger-shaped mark towards the front margins of the front wings. Significant captures of this moth have been in the southern half of Minnesota. Black cutworm trapping records for Minnesota are available at the University of Minnesota web site:

www.ent.agri.umn.edu/cutworm/

    The other moths that are present include the variegated cutworm, Peridroma saucia, and Agrotis volubilis. These moths lack the characteristic markings of the first two moths. Variegated cutworm can be a problem in crops, but typically it is more of a concern in vegetable gardens.

 

ARMYWORMS . . . What to watch for later

    Armyworms are olive-green or greenish-brown with dark stripes running the length of the back along with two orange stripes on each side of the body. Eggs of armyworms are laid at night in folded leaves or under leaf sheaths and on small grain plants. The eggs look like small white beads and are in masses. Eggs hatch in about eight to ten days.

    During the day, armyworm larvae can be found under plant trash, clods of soil and in soil cracks. They feed at night. Smaller worms will feed on lower leaves. As they increase in size, they tend to feed higher up on the plant. They feed for about three to four weeks.

    Sampling for armyworms should include inspections at a minimum of five locations using an X pattern to spread the sample sites out across the field. In small grains, treatment for armyworms is advised when four to five or more larvae are found per square foot. In corn, treatments should be applied when two or more larvae occur per plant on 25 to 30 percent of the stand or there is one per plant on 75 percent of the stand.

Insecticides for Armyworm Control

Insecticide

Corn

Wheat

Small Grains*

Ambush

X

   

Asana

X

   

Carbaryl

X

X

 

Ethyl or Methyl Parathion

 

X

X

Lannate

X

 

X

Lorsban

X

 

X

Malathion

X

 

X

Penncap-M

X

 

X

Pounce

X

   

Warrior

X

X

 

    *Small grains = wheat, barley and oats

 

WIREWORM ACTIVITY LINGERS

    Reports from around the state, particularly on the eastern half, indicate wireworms are causing problems with young seedlings, especially corn. Slow plant emergence and growth gives wireworms the upper hand. With some warming and drying expected, plants should grow and wireworms should move a little deeper into the soil profile. Rescue treatments are not recommended, but consider seed treatments with an approved insecticide for remaining crops to be planted. Remember, we still must deal with Seedcorn maggot, as well, and these treatments will aid with them.

 

GRASSHOPPERS STARTING IN THE WEST

    With a little warm weather, grasshoppers are emerging quickly. Jan Knodel, Crop Protection Specialist is reporting grasshopper hatch in the Minot Region. Bob Hoffbeck, consultant, has indicated significant hatching in McLean County in fields where dry beans and sunflowers were grown last year.

    Watch for hatching hot spots in areas where late season crops were grown last season. Those are the sites where adults went to lay eggs last season.

 

FLEA BEETLES MOVING TO CANOLA FAST

    With the arrival of some decent weather, the flea beetles are coming out of overwintering and moving quickly to any canola that has emerged. There are some concerns about whether the Gaucho treatments are holding up in the fields. Here are some observations from work that has been done with Gaucho:

    There are still a lot of beetles in treated fields: The Gaucho, or imidacloprid, is absorbed and translocated through the plant to the leaves. When the insects feed on a treated plant, the insecticide inhibits feeding. Death, however, may take a little longer. LoAyne Voigt, Renville Extension Agent, reported seeing sluggish beetles in treated fields she was inspecting, a likely sign of poisoning.

    How long does the protection last: Gustafson reports that protection from flea beetles is provided for 17 to 21 days after emergence. Unfortunately, the slow emergence and growth is putting many of these fields at the 21 to 28 day range from our planting date. Watch these fields carefully. Under these conditions, the concentration of the insecticide in the plant may be declining to the point where protection is incomplete.

    How about some guidelines to tell me if the insecticide is working: Mike Weiss, former NDSU entomologist, observed over the years that the flea beetle feeding pits were very small on treated plants. Often, treated plants had numerous, but small pits. Untreated plants would have fewer, but larger pits.

    Things to keep in mind while monitoring: If you are in Gaucho treated fields, observe damage and flea beetle activity. If feeding pits are small and beetles are sluggish, the insecticide should be working. Scout again in a couple of days. So, if pits are large and beetles active a rescue treatment may be warranted. Once the first true leaf is expanded, the plants should be able to tolerate future feeding. If pits are small but beetles appear very active, they may have just arrived and scouting the field the next day would be advisable.

Phillip Glogoza
Extension Entomologist
pglogoza@ndsuext.nodak.edu

 


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