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ISSUE 8   July 3, 2008

SCOUT FOR LEAFY SPURGE FLEA BEETLES

Leafy spurge flea beetles (Aphthona species - see photograph) are an effective means of controlling the noxious weed leafy spurge in North Dakota.

brown legged spurge flea beetle
Brown-legged spurge flea beetle, Apthona lacertosa (Rosenhauer).
(Photo courtesy USDA APHIS PPQ Archive)

This group of flea beetles is host-specific to the leafy spurge plant, which makes them an ideal biological control choice. The southern half of North Dakota has accumulated over 1,000 growing degree day (GDD) and scouting should begin for adult leafy spurge flea beetles. Flea beetles should be collected between 1,200 and the 1,600 (see following map) using the sunflower GDD on NDAWN.

Sunflower GDD map

Adult flea beetles can be collected with sweep nets. After late July, flea beetles begin to lay eggs and should not be moved. The flea beetle typically take three to five years to establish and impact leafy spurge infestations.

New publications from South Dakota State University offer tips on using flea beetles to help control leafy spurge. SDSU Extension Extra 8161, "Managing Leafy Spurge Flea Beetle Releases in South Dakota," is available online in PDF format at agbiopubs.sdstate.edu/articles/ExEx8161.pdf. SDSU Extension Extra 8162, "Leafy Spurge Flea Beetle Collection Recommendations," is online at agbiopubs.sdstate.edu/articles/ExEx8162.pdf

 

WHEAT MIDGE RISK FORECAST LOW AND EMERGENCE DELAYED

For the wheat midge risk forecast in 2008, NDSU Extension agents collected a total of 1,910 soil core samples from 191 fields in 20 counties during the fall of 2007. Lower levels of overwintering wheat midge larvae were observed in the 2007 soil survey than previous years (see 2007 Wheat Midge Larval Survey ND map).

2007 wheat midge larval map

Wheat midge populations ranged from zero to 678 midge larvae per square meter, with most of the state having less than 200 midge larvae per square meter. Approximately 56 percent of the soil samples were positive for wheat midge larvae, with an average of 107 larvae per square meter. In 2008, areas with more than 500 midge larvae per square meter in Cavalier and Towner counties decreased from the previous year. A small, new pocket, with more than 500 midge larvae per square meter was discovered in Divide County in northwestern North Dakota. There are also several small pockets of lower numbers of 201 to 500 midge larvae per square meter in central Divide, south-central Burke, west-central Renville, east-central Mountrail, central Ward, northern Benson, eastern Eddy, northern Ramsey Counties and a larger pocket in central Cavalier County. Areas with more than 200 midge larvae per square meter should be scouted to determine if economic population levels exist in wheat/durum fields in the susceptible crop stage heading to early flowering. No 2007 soil samples collected had more than 1,200 midge larvae per square meter, which is considered a high-risk for infestation in 2008.

The parasitism rate of the tiny parasitic wasp, Macroglenes penetrans (see photograph), has doubled from an average parasitism rate of 8 percent in 2007 to 16 percent in 2008 (see 2007 Wheat Midge Larval Survey - % Parasitism ND map). This wasp lives inside wheat midge larvae and eggs, and will emerge the following spring. It kills the developing wheat midge larva. The parasitism rate typically ranges from 0 percent to 100 percent each year, with higher rates occurring in areas where midge populations have been high the past few years. Counties with parasitism rates of more than 50 percent include Burke, Mountrail, Ward, McHenry, McLean and Bottineau counties.

Parasitoid of wheat midge
Parasitoid, Macroglenes penetrans, of wheat midge

(photo courtesy Saskatoon Res. Centre, Canada)

2007 Wheat Midge parasitism rate map

The wheat midge soil survey is supported by the North Dakota Wheat Commission.

A degree day (DD) model using daily temperatures to calculate DD accumulation allows for more accurate prediction of local adult emergence. Events for the midge population (degree day base = 40 F) are listed in the table below.

DD

Biological Event

450

Midge breaks the larval cocoon and moves close to soil surface to form the pupal cocoon.

1300

10% of the females will have emerged.

1475

About 50% of the females will have emerged.

1600

About 90% of the females will have emerged.

Typically, wheat midge is emerging during the first week of July in the northern counties of North Dakota. However, this year the DDs are behind normal and only near 1,000 DD in the northern tier (see Wheat Midge DD map). Wheat midge DD maps for North Dakota are available on the NDAWN website:

http://ndawn.ndsu.nodak.edu/wheat-midgedd-form.html

Wheat midge GDD map

 

WHEAT STEM SAWFLY EMERGING

Field reports indicate that adult wheat stem sawfly has begun to emerge in southwestern North Dakota. High numbers of adult sawflies have been collected using sweep nets in spring wheat fields at Hettinger, Scranton, Regent, and Mott. The sex ratio is 2:1 (male to female) sawflies. Adults are small, black wasps with three yellow bands around the abdomen (see photograph). Males emerge earlier than females. Adults live only 7-10 days. They are inactive insects that spend most of their time resting with heads down on grass stems. Females prefer to lay eggs in wheat that has not reached the jointing stage (stem elongation). Plants in the boot stage are not preferred for egg laying. Currently, there are no monitoring methods or economic thresholds that have been established for adult wheat stem sawfly.

sawfly
Adult wheat stem sawfly

These is one generation of wheat stem sawfly per year. Female sawflies deposit eggs into the elongating stems of host plants (wheat, rye, triticale, barley) in early summer. The developing larvae feed and move up and down the length of the stem interfering with water and nutrient flow to the developing grain head. As the wheat plant matures, and usually prior to harvest, the larva moves down to the base of the stem and chews a notch around the inside of the stem. Feeding injury causes reduced yield and quality of grain (lower protein and kernel weight), and lodging problems.

How can I control wheat stem sawfly? Currently, there are no insecticide recommendations for control for wheat stem sawfly. The best control strategies include seeding solid-stemmed varieties that are resistant to wheat stem sawfly or planting alternative non-host crops. Swathing infested wheat at 40% kernel moisture will help save stems before they are cut by sawfly and lodging losses. NDSU is conducting research on wheat stem sawfly in 2008 on:

 

CANOLA INSECT TRAPPING

All trap counts for bertha armyworm and diamondback moth have been low so far this year. Like so many other insect pests that overwinter in North Dakota, emergence of bertha armyworm has been delayed due to cool spring temperatures. The migration risk forecast for adult diamondback moths is also low. Maps on trapping results will be posted on the NDSU Extension IPM Survey website. Click on "Canola Trap Network."

http://www.ag.ndsu.nodak.edu/aginfo/ndipm/index.htm

Janet J. Knodel
Extension Entomologist
janet.knodel@ndsu.edu


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