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ISSUE 6   June 17, 2010

CONTINUE TO BE VIGILANT SCOUTING FOR CUTWORMS

Just a friendly reminder that the late season cutworms will continue to be active throughout June. So, continue to scout for cutworms, especially since crops have been growing slowly. Excessive cool, wet soils tend to amplify stand reduction by slowing plant development relative to cutworm feeding. The Extension Entomology office has received an increased number of field reports on cutworm feeding from many different crops (sunflowers, canola, alfalfa, sugar beets, soybeans) this past week.

For economic thresholds and insecticides registered in North Dakota for cutworm control, consult the 2010 Field Crop Insect Management Guide at:

http://www.ag.ndsu.edu/pubs/plantsci/pests/e1143w1.htm

 

ALFALFA WEEVIL DEGREE DAY UPDATE

Growing degree days (base 48 F) for alfalfa weevil indicate that the central region of North Dakota is at risk for larval feeding activity (430 to 595 DD: Figure 1). There has been one report of weevil activity from the Jamestown area. Cool and wet weather has slowed weevil development and alfalfa cutting. As soon as it dries out, timely cutting should provide good alfalfa weevil control in the first cutting. Remember to scout second cutting for weevil feeding under the windrows.


Figure 1.
Alfalfa weevil degree day map (NDAWN)

Note: Please see issue #3 of Crop & Pest Report for scouting and pest management details.

 

SCOUTING FOR LEAFY SPURGE FLEA BEETLES

Leafy spurge flea beetles (Aphthona species) (Fig. 2) are an effective means of controlling leafy spurge in ND.


Figure 2.
Leafy spurge flea beetles, Aphthona flava (N.E. Rees, USDA ARS, bugwood.org)

This group of flea beetles is host-specific to the leafy spurge plant, which makes them an ideal biological control choice. The accumulated growing degree days (AGDD) for sunflower (base of 44 F) can be used as a guide to determine when to begin scouting for adult flea beetles. Begin scouting for adult flea beetles when the AGDD approaches 1,000. Flea beetles should be collected between 1,200 and the 1,600 using the sunflower GDD from NDAWN. The southeastern region of North Dakota has accumulated over 1,000 growing degree days (GDD, Fig. 3) and scouting should begin for adult leafy spurge flea beetles. Use the sunflower degree days/growth stage application in NDAWN and enter "2010-03-01" for planting date and select "degree day" for map type.

http://ndawn.ndsu.nodak.edu/sunflowergdd-form.html


Figure 3.
Leafy spurge flea beetle degree day map (NDAWN)

Adult flea beetles can be collected with sweep nets. After late July (or 1,600 AGDD), flea beetles begin to lay eggs and should not be moved or collected. Leafy spurge flea beetles typically take three to five years to establish and impact leafy spurge infestations.

To find collecting sites for leafy spurge flea beetle, contact your local county extension agent or weed control officer. A listing of the weed control officers by county can be found on the North Dakota Weed Control Association website:

http://ndweeds.homestead.com/10_County_City_Weed_Boards_Directory.pdf

 

ECONOMIC THRESHOLDS FOR CEREAL GRAIN APHIDS

Fortunately, the cool temperatures and rains have kept aphid populations low in North Dakota (Fig. 4). This weather is also conducive for entopathogens (fungal diseases) that attack aphids, further reducing aphid populations. There also are many labybird beetles and other predators that feed on aphids and can be observed in fields now.


Cereal aphids


Figure 4.
Cereal aphids in wheat map (IPM Survey, J. Walker)

Winter wheat is starting to flower and past the susceptible stages (vegetative to boot) where aphids may cause significant yield loss. So, no insecticides are recommended in winter wheat at this point.

There have been some questions about the two different sampling methods to make a decision on whether to treat or not for cereal aphids in small grains that was reported in the last issue of the Crop & Pest Report.

The "85% of the stems infested" (where infested is defined as one or more aphids on a stem) comes from a sequential sampling model developed by Boeve and Weiss at NDSU in the late 90s. The specific sampling method is described as: Walk into the field 100 ft from the edge before you begin sampling for aphids. Sample one stem every 25 paces. A stem is considered infested if one or more aphids are present. Sample at least 20 to 100 stems in this manner for every 100 acres. Divide number of infested stems by number of stems sampled to arrive at percent infested stems.

The other sampling method uses 12-15 aphids/stem. For this sampling method, growers should examine at least 20 stems at 5 different locations in the field away from field edges. If the average is 12-15 aphids/stem, treatment is warranted. If not, continue to monitor for growing aphid populations. There is some flexibility to wheat prices built into this sampling method. When the price for wheat is low, use the higher threshold of 15 aphids/stem and vice versa.

Without going into the research details, these are basically two different sampling methods for making decisions on whether to treat or not treat for cereal aphids. Producers and scouts can use either action threshold to arrive at the same decision.

Late vegetative through boot stage is the most critical time to scout and treat for cereal aphids to prevent yield loss.

 

PEA APHIDS DETECTED IN PULSE CROPS

Low levels of pea aphids have been detected in peas grown in the north central and northwest regions of North Dakota. This is the most common insect pest found in field pea. They are small, about 1/8+ inch long, and pale green (Fig. 5).


Figure 5.
Pea aphids (P. Beauzay, NDSU)

Last year, producers were surprised by pea aphids in their pea fields and some may have lost up to 10 bu/acre. So, it is wise to scout pea fields for aphids when 50-75% of the peas are flowering by using either a sweep net or examining the number of aphids per plant tip. Take 180-degree sweeps using a 15-inch sweep net or check at least five 8-inch plant tips from four different locations in the field. Population estimates should be calculated by averaging counts taken from four separate areas of the field.

Economic Thresholds:

Economic thresholds may vary depending on the value of the crops and cost of control, as well as impacts of precipitation and heat stress. The economic threshold in peas at $5.71 per bushel and average control cost of $6.73-$9.25/acre is 2 to 3 aphids per 8-inch plant tips, or 9 to 12 aphids per sweep (or 90 to 120 aphids per 10 sweeps), at flowering. If the economic threshold is exceeded, a single application of insecticide when 50% of plants have produced some young pods will protect the crop against yield loss and be cost-effective. Cultivars of peas may also vary in their tolerance to feeding by pea aphids. Thus, economic injury levels may differ between cultivars. The economic thresholds presented above were developed using "Century" field peas.

Aphid feeding on peas in the flowering and early pod stage can result in lower yields due to less seed formation and smaller seed size. Protein content and other quality issues do not appear to be affected.

Research in Manitoba has shown that insecticides applied when pods first form protects pea yield better than earlier or later applications. Control at the early pod stage provides best protection through the pod formation and elongation stages, which are very sensitive to aphid damage.

For insecticides registered in North Dakota for pea aphid control, consult the 2010 Field Crop Insect Management Guide at:

http://www.ag.ndsu.edu/pubs/plantsci/pests/e1143w1.htm

 

WATCH GRASSHOPPER POPULATION LEVELS

The silver lining to this cool, wet weather is that it has not been favorable for the predicted grasshopper outbreak in rangeland. However, there are some increasing numbers in Emmons and Kidder Counties in the south central region of North Dakota (Fig. 6). If the weather turns more favorable (hot and dry), grasshoppers populations can increase quickly. So, continue to scout ditches and field edges for grasshopper nymphs (young grasshoppers without wings). The threatening level is 50-75 nymphs per square yard in ditches and 30-45 nymphs per square yard in fields. A handy tools for estimating grasshopper numbers is the sweep net. Four 180-degree sweeps with a 15-inch sweep net is equal to one square yard.


Figure 6.
Grasshopper map (IPM Survey, J. Walker)

 

ADULT WHEAT STEM SAWFLY EMERGING

Joseph Stegmiller, my M.S. graduate student, has collected adult wheat stem sawfly in the southwest region (Scranton, Regeant, Hettinger, Mott) of North Dakota. Another sawfly report from the central region (Steele) came in today. There are NO insecticide strategies that work for control of the adult wheat stem sawfly. It is interesting to note when they emerge. A new NDSU Extension factsheet entitled Integrated Pest Management of Wheat Stem Sawfly is available at:

http://www.ag.ndsu.nodak.edu/aginfo/entomology/entupdates/sawfly/e1479.pdf

This factsheet was published with cooperation and support from the North Dakota Wheat Commission.

 

EPA MOVES TO TERMINATE ALL USES OF INSECTICIDE ENDOSULFAN TO PROTECT HEALTH OF FARMWORKERS AND WILDLIFE

WASHINGTON - The U.S. Environmental Protection Agency (EPA) is taking action to end all uses of the insecticide endosulfan in the United States. Endosulfan, which is used on vegetables, fruits, and cotton, can pose unacceptable neurological and reproductive risks to farmworkers and wildlife and can persist in the environment.

New data generated in response to the agency's 2002 decision have shown that risks faced by workers are greater than previously known. EPA also finds that there are risks above the agency's level of concern to aquatic and terrestrial wildlife, as well as to birds and mammals that consume aquatic prey which have ingested endosulfan. Farmworkers can be exposed to endosulfan through inhalation and contact with the skin. Endosulfan is used on a very small percentage of the U.S. food supply and does not present a risk to human health from dietary exposure.

Makhteshim Agan of North America, the manufacturer of endosulfan, is in discussions with EPA to voluntarily terminate all endosulfan uses. EPA is currently working out the details of the decision that will eliminate all endosulfan uses, while incorporating consideration of the needs for growers to timely move to lower-risk pest control practices.

Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), EPA must consider endosulfan's risks and benefits. While EPA implemented various restrictions in a 2002 re-registration decision, EPA's phaseout is based on new data and scientific peer review, which have improved EPA's assessment of the ecological and worker risks from endosulfan. EPA's 2010 revised ecological risk assessment reflects a comprehensive review of all available exposure and ecological effects information for endosulfan, including independent external peer-reviewed recommendations made by the endosulfan Scientific Advisory Panel.

Endosulfan, an organochlorine insecticide first registered in the 1950s, also is used on ornamental shrubs, trees, and herbaceous plants. It has no residential uses.

For more information:  http://www.epa.gov/pesticides/reregistration/endosulfan/endosulfan-cancl-fs.html

EPA Contact Information: Dale Kemery kemery.dale@epa.gov 202-564-7839, 202-564-4355

Registered agricultural formulations in ND include Thionex 3EC and Thionex 50W. These products are labeled for mostly fruit and vegetable use, but also for potatoes, sweet corn, and forestry sites. Endosulfan is also the active ingredient in Avenger Insecticide Cattle Ear Tags. (Source, Jim Gray, North Dakota Department of Agriculture)

 

FUN INSECT QUESTION: What are these spiny caterpillars (larvae) feeding on willow?


Figure 7.
Mystery insect (Aimee Thapa, NDSU)

This is the larva of the beautiful Mourning Cloak butterfly, Nymphalis antiopa (Lepidoptera: Nymphalidae). Larvae feed gregariously on willow, poplar, elm, birch or hackberry. They are black and spiny with fine white speckles and a row of red spots running down the back. It is also called the ‘spiny elm caterpillar.’ The adult butterfly is a strong flyer and migrates into North Dakota from Mexico each year. It is primarily a woodland butterfly and also the State Insect of Montana.

Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu


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