NDSU Crop and Pest Report

Entomology


ISSUE 2   May 13, 2004

WEEVIL DAMAGING SUGARBEET EAST OF FARGO-MOORHEAD AREA

A small (1/4 to 1/2 inch), grayish, spotted, broad-nosed weevil has been found feeding on sugarbeet seedlings. One report where specimens were submitted for identification was from the Lake Park, MN area. This weevil has been observed damaging beets in other years. The most recent report was from 1997 when these weevils caused damage to beets in the southern Minnesota production area.


Tanymecus confusus

The 1997 report is printed in the Sugarbeet Research and Extension Reports, Volume 28, pages 256_257. It described the situation observed in four beet fields in Chippewa County and two fields in Lac Qui Parle County, near Montevideo in early June, 1997. The field areas affected ranged from being a few feet in diameter to about one half of an acre. Some of the infested areas were damaged enough that re-planting was required.

Though the biology of this insect is not fully known, a similar species in Europe (Tanymecus palliatus) overwinters as adults in the ground or in dead plant residue. When adults emerge in the spring, females bore a small hole in the plant and deposit eggs. Eggs hatch in about a month, where the larvae will feed on host plant tissue until adulthood. The adult feeding is of concern where these beetles are present.

The published host plant preference identifies broadleaf weeds such as cocklebur (Xanthium spp) Pigweed (Amaranthus spp) and Ragweed (Ambrosia) spp).

The weevils prefer to consume leaf tissue from the outside edge of leaves to the main vein. They do not consume the vein (mid-rib) of the leaf. No cotyledon feeding was observed, but it should not be ruled out. If enough leaf tissue is consumed, the plant will die; the younger the plant the more susceptible to feeding and mortality. The adults appear to be nocturnal feeders. To find adults during the day, dig around the base of plants that appear to have feeding damage. Adult T. confusus are found just below the soil surface.

  
Range of feeding damage observed
for Tanymecus confusus in 1997.

There are no current recommendations for when management is needed. The best guideline would be to assess the risk to stand establishment. No insecticides list this insect on labels. Insecticides labeled on sugarbeet, such as Asana, Lorsban, and Mustang should provide control and protection.

 

SECTION 18 CRISIS EXEMPTION FOR SUNFLOWER SEED TREATMENT IS EXPECTED

It is expected that the North Dakota Department of Agriculture will declare a crisis, May 17 or later, for the temporary use of the seed treatment ConcurŽ as a planter box treatment for sunflower seed to manage wireworms. ConcurŽ contains the insecticide imidacloprid and the fungicide metalaxyl. ConcurŽ is currently labeled for treating corn seed. A copy of the crisis exemption label must be in the possession of the user. A copy of the label will be posted at:

http://www.ag.ndsu.nodak.edu/aginfo/pesticid/sec18_2004.htm

The proposed seed treatment application rate of imidacloprid for this crisis exemption is ConcurŽ at 8 oz/100 lbs of sunflower seed applied as a dry mixture in the planter box prior to planting.

Until 1999, when sunflower tolerances were dropped in the re-registration process, lindane was the only seed treatment insecticide labeled for wireworms on sunflower and was used to treat approximately 75% of the crop nationwide. Existing stocks of Isotox (lindane) seed treatment were used until depleted in 2003. CruiserŽ (thiamethoxam) was approved for commercial seed treatment use on sunflower in 2003. At this time, it is estimated that 30% of sunflower seed for planting was commercially treated with CruiserŽ. With the commercial treating season having already ended and the treated seed sold-out, that leaves 70% of the seed unprotected. This exemption should provide growers with an on-farm seed-treatment solution to help manage wireworm damage.

Imidacloprid is the same active ingredient contained in the GauchoŽ seed treatments used in canola, small grains, and other crops. In addition, the product contains the fungicide metalaxyl, used to control seedling blight caused by Pythium.

Phillip Glogoza
Extension Entomologist
pglogoza@ndsuext.nodak.edu


NDSU Crop and Pest ReportTop of PageTable of ContentsPrevious PageNext Page