NDSU Crop and Pest Report

Entomology


ISSUE 4  May 22, 2003

SUGARBEET ROOT MAGGOT:  PEAK FLY EXPECTED EARLY

According to the NDSU sugarbeet root maggot developmental model, peak fly activity is likely to be slightly earlier than normal this year. Soil degree-day (DD) accumulation occurred at fairly rapid rates during the 2nd and 4th weeks of April and, with the exception of the past 2 days, DDs continue to be added at a relatively quick pace compared to previous years.

A rainfall event can have significant impacts, both positive and negative, on overwintered root maggot populations. A gradual "soaker" rain on a warm soil surface can percolate heat energy into the soil profile and accelerate development; however, excessive rainfall that leads to prolonged saturation can result in substantial levels of mortality.

Degree-day accumulations as of 18 May suggest that, depending on latitude, peak fly activity in current-year beets will take place in the first 2 to 8 days of June this year. More southerly areas may even see activity peak during the last week of May. Remember – warm (80 degrees Fahrenheit or above) daytime weather is also needed for the actual peak to occur. Windy and/or rainy weather can delay or diminish what would have been the true peak.

For guidance on anticipated populations in the region or for specific information on sugarbeet root maggot management, please refer to the "Insect Control" section of the 2003 Sugarbeet Production Guide or the "Sugarbeet Insects" section of the 2003 Field Crop Insect Management Recommendations for more detail and specific product recommendations. The respective WWW locations for online versions of these publications are:

http://www.sbreb.org/Production/production.htm

and

http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm

Mark Boetel
Research & Extension Entomologist
mboetel@ndsuext.nodak.edu

 

MOSQUITO TRAPS . . . ARE THEY THE SILVER BULLET?

The recent rains and two confirmed West Nile Virus cases in horses are prompting many questions about mosquito control and personal protection. One of the most popular topics of interest has been the effectiveness of the widely publicized mosquito traps now being marketed. There have been numerous studies established around the country designed to test just that. The American Mosquito Control Association (AMCA) has recently prepared a summary document regarding these traps and how they might fit into a mosquito control program.

The entire article can be found on the AMCA web site, located at:

http://www.mosquito.org/

The general idea behind these trapping devices is to reduce the number of mosquitoes that pester the homeowner and their family.

The traps use attractants that lure the host-seeking female mosquitoes to the trap. Some devices use an impeller fan that draws the mosquitoes into a net, where they are trapped and eventually dye from desiccation. Some trapping systems use a sticky surface to capture the mosquitoes when they land. Others may rely on the popular electric grid approach which electrocutes mosquitoes upon contact. In general, all these devices require some level of regular maintenance to clean them of their “prey”.

The vast majority of these traps use carbon dioxide, produced either through the combustion of propane or with a CO2 cylinder and release rate between 350m and 500 ml/min. The plume of CO2 produced mimics exhaling humans and makes these traps specific for capturing blood-feeding insects. This is an improvement over older trap designs, such as black-light traps, which captured mostly non-target insects such as moths and beetles. The CO2 is often combined with 1-Octen-3-ol, a derivative of gasses produced in the rumen of cows, to increase attractiveness by several orders of magnitude. The 1-Octen-3-ol is slow-released at a rate of ca. 0.5 mg/h.

The process of a mosquito searching for a blood meal is a complex pattern of behaviors, relying on multiple sensory cues that may be visual, thermal, or olfactory. These complex behaviors can explain some of the variations in trapping efficiency for these units noted for certain species of mosquitoes at different times. There certainly is variation among trap designs in their ability to attract and capture mosquitoes.

Nonetheless, these devices will, indeed, trap and kill measurable numbers of mosquitoes. The big question is whether these devices will produce a noticeable reduction in the mosquito population. Perception of effectiveness at achieving this goal may depend upon a number of factors, for example, an individuals tolerance level for mosquitoes, the absolute size of the mosquito population, the proximity, size and type of breeding habitat that produces the source of re-infestation, wind velocity and direction, and species of mosquito present, among many other things. Depending upon the traps placement, wind direction, and trapping efficiency, there is a risk that these traps may actually draw more mosquitoes into an area than they can possibly catch. Therefore, it is still strongly recommended that repellents be used when outdoors during periods of mosquito activity and practice other source reduction methods to produce a more comprehensive level of relief.

In conclusion, the AMCA article states, “Please be cautioned against putting too much faith in traps as your sole means of control. These traps represent an evolving technology that is a most welcome addition to our mosquito control armamentarium. Their potential is great, but shouldn’t be overestimated. It’s highly unlikely that these devices, whatever their improvements, will ever fully supplant organized community-wide mosquito control programs, for there is no single silver bullet that will prove to be the ultimate answer to mosquito problems. Effective mosquito management requires integrating a variety of available control strategies i.e. surveillance, source reduction, biological control methods, traps, environmentally friendly larvicides, and, when necessary, application of public health adulticides, into a comprehensive program that exploits known mosquito vulnerabilities.”

Some comments on cost differences:
Power supplies for different trap types will vary. Some are totally self-contained, using propane to provide both power and the source of carbon dioxide for the attractant. These units have the advantage of portability, allowing them to be placed at a considerable distance away from home-sites. This may be an important consideration on larger properties such as those over an acre in area, by allowing mosquitoes to be intercepted long before they come into the vicinity of human activity. This portability comes at a price, though, for the thermoelectric generator that uses excess heat from the combustion process to generate electricity to run the intake fans is quite expensive. Most units rely upon power cords and AC current from outlets. This limits them to smaller areas served by extension cords, but their price is less than their self-contained counterparts.

For more information on mosquito control and health issues such as West Nile Virus, visit the following web sites:

Mosquito Management in North Dakota. NDSU Extension Publication E-472. 2000.
http://www.ext.nodak.edu/extpubs/plantsci/pests/e472w.htm

Centers for Disease Control - Q & A on West Nile Virus
http://www.cdc.gov/ncidod/dvbid/westnile/q&a.htm

Comparative Efficacy of Insect Repellents against Mosquito Bites. 2002. Mark S. Fradin, M.D., and John F. Day, Ph.D.New England Journal of Medicine, Volume 347:13-18 July 4, 2002 Number 1.
http://content.nejm.org/cgi/content/full/347/1/13

Grand Forks Mosquito Control Program
http://www.grandforksgov.com/publichealth/mosqu.htm

Phillip Glogoza, Extension Entomologist
pglogoza@ndsuext.nodak.edu
 

CANOLA: FLEA BEETLE ALERT!

Large numbers of flea beetles are active in overwintering areas and volunteer canola has been severely damaged. There were high numbers of flea beetles last summer in swathed canola field across North Dakota, especially in the north central and north eastern regions. Canada also reported more flea beetles than usual in northeast Manitoba and southern Alberta (L. Dosdall, J. Gavloski). With the cool, wet weather in early May, flea beetles remained relatively inactive and slow to emerge. The weather forecast is now for a warming trend, so producers should expect flea beetles to start moving into spring planted fields. Flea beetles become very active when temperature reach >68 degrees F. So, fields should be scouted regularly until canola plants are near the six-leaf stage. Fields with seed treatments, like Helix xtra from Syngenta or Gaucho Platinum from Gustafson also need to be monitored, especially the early-planted fields. The protection window is only about 21 days after planting with the insecticide-treated canola seed. The early-planted canola from early May or late April is just starting to come out of the ground at day 20 plus after planting. Most of the insecticide protection is unfortunately gone. Research has shown that a foliar spray on top of the insecticide-treated canola seed provides the best protection from flea beetles and the highest yields. Please see 2002 Virtual Tour-Planting Date/Insecticide Study for Flea Beetle Management on Canola website:

http://www.ag.ndsu.nodak.edu/minot/pest/pn.htm

Seed treatment isn’t always enough; a foliar insecticide may be required to save the crop. So, please scout your canola crop closely. The economic threshold for control is reached when 25% of the leaf surface is destroyed and flea beetles are active. My forecast is that "flea beetles will emerge in extremely high numbers late this week into Memorial Day weekend, similar to last year." Two synthetic pyrethroids are available as foliar rescue sprays: Capture at 1.3-2.6 fl oz/A from FMC and Warrior at 1.92- 3.84 fl oz/A from Syngenta. The higher rates would provide a longer residual of >7 days. These pyrethroids are compatible with herbicides registered in canola for tank mixing.

Janet J. Knodel
Area Extension Specialist Crop Protection
North Central Research and Extension Center
Minot, ND

 

GRASSHOPPERS IN SUGARBEETS

A few fields in the Moorhead Factory District were sprayed for grasshoppers. Look for grasshoppers in uncultivated ground and field margins early in the season when scouting. When 20 or more adult grasshoppers per square yard are found in the field margins, spraying is recommended. With timely scouting, grasshoppers can be easily controlled by spraying the field margins.

Insecticide recommended for grasshopper control include: Asana XH, Lorsban 4E, Mustang 1.5 EW, Diazinon AG 500, and Methyl Parathion.

Please check the 2003 Sugarbeet Production Guide, page 71, for more information.

Mohamed Khan
Extension Sugarbeet Specialist
mkhan@ndsuext.nodak.edu


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