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ISSUE 4   June 3, 2010

UPDATE ON ALFALFA WEEVIL GROWING DEGREE DAYS

Growing degree days (base 48 F) for alfalfa weevil indicate that the southeast and east central regions of North Dakota are at risk for larval feeding activity (Fig. 1). However, most of the alfalfa fields have been or will be cut soon killing weevil larvae by dessication and/or mechanical injury. Timely cutting should provide good alfalfa weevil control in the first cutting this year. However, scout the second cutting for feeding injury and treat if 50% of crowns have weevil feeding and re-growth is delayed 3-6 days. Feeding injury is often concentrated underneath the windrows.


Figure 1.
Alfalfa weevil degree day map (NDAWN, NDSU)

Note: Field scouting for alfalfa weevil is initiated at 300 DD. Major feeding by the alfalfa weevil larvae will occurs from 430 to 595 DD (2nd - 4th instar). At greater than 600 growing degree days feeding normally stops and adult emerge. Please see issue #3 of Crop & Pest Report for scouting and pest management details.

 

SOYBEAN APHIDS APPEAR IN SW MINNESOTA!

Bruce Potter, IPM Specialist in SW Minnesota, reported that soybean aphids have shown up in Nicollet County in south central Minnesota. These reports are coming from fields that were planted early and near buckthorn, the overwintering host of soybean aphid. So, these fields will obviously be at higher risk for early infestation by soybean aphid.

Soybean aphid scouting should begin in the early vegetative stages (V3-V4 stage) and concentrate on those fields near buckthorn. Remember to check at least 20 plants in 5 locations (4 plants per location) throughout the field and to average the number of aphids per plant (not leaflet). This time of year the small, yellow soybean aphids (Fig. 2) are typically found in the upper leaves of plant and on the underside of leaf.


Figure 2.
Soybean aphids (P. Beauzay, NDSU)

NO treatment is recommended in the early vegetative crop stages and is discouraged so insecticides do NOT reduce the presence of beneficial insects (predators and parasitoids). The critical growth stage for making most soybean aphid treatment decisions is in the late vegetative to early reproductive stages (R4 = ¾ inch pods). Assessing aphid populations at this time is critical. Typically aphid insecticide treatments are necessary in mid-July to mid-August. The economic threshold is 250 aphids/plant when populations are actively increasing in 80% of field. For those of you who are complaining about counting up to 250 aphids per plant, a handy picture guide for estimating the number of aphids per leaf (Fig. 3) has been published by University of Wisconsin and is available at:

http://www.plantpath.wisc.edu/soyhealth/pdf/sba_scout.pdf


Figure 3.
Soybean aphid scouting visual guide
(University of WI - Extension)

 

DIAMONDBACK MOTH ARRIVES EARLY

Even though some canola fields have not emerged yet, diamondback moths have arrived early from the southern states. Adult moths (Fig. 4) have been detected in pheromone traps in Manitoba, Canada, and trap counts are already quite high in the eastern region (J. Gavloski, Entomologist, Manitoba Agriculture, Food and Rural Initiatives). IPM Scouts will be getting their pheromone traps out this week in North Dakota to start monitoring.


Figure 4.
Diamondback moth adult (G. Fauske, NDSU)

The early migrants lay eggs on the lower leaves of canola, mustard, and rapeseed. Larvae hatch from the eggs and feed on first leaves. The small, greenish larvae (Fig. 5) make tiny, irregular holes in the leaves and actually mine inside the leaf as a leafminer for the first week (Fig. 6). Foliar feeding injury to seedlings and 2-4 leaf canola plants has caused significant stand losses in the north central region of North Dakota in past years. Larval feeding injury is worse when plants are under drought or heat stress. So, be sure to scout canola fields for diamondback moth larval feeding.


Figure 5.
Diamondback moth larva (J. Knodel, NDSU)


Figure 6.
Diamondback moth larval mine (J. Knodel, NDSU)

There is no economic threshold that has been developed for diamondback moth in the seedling and early vegetative stages. However, 25% defoliation or stand loss will caused economic losses in canola. Insecticide seed treatments will not control diamondback moth larva and a foliar rescue insecticide application must be made.

 

COLORADO POTATO BEETLES EMERGING

The first overwintering Colorado potato beetle adults have been observed this past week in our insecticide plots near Glyndon, Minnesota. Emergence will continue through June. The adult is 3/8 inch long, with oval body and a yellow-brown color with 5 black stripes on each wing cover (Fig. 7). This beetle is the most common and destructive leaf feeding pest of potato in commercial potato fields and backyard gardens. Scouting and pest management guidelines will be summarized in the next issue of Crop & Pest Report, so stay tuned!


Figure 7.
Colorado potato beetle adult (J. Knodel, NDSU)

 

EPA UPDATE ON ORGANOPHOSPHATE INSECTICIDES

The following article was extracted from the EPA Pesticide Update and summarizes EPA’s statement regarding the pediatrics article: "Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate Pesticides."

A study published in the journal Pediatrics concludes that "organophosphate (OP) exposure, at levels common among U.S. children, may contribute to ADHD presence."

The Agency is taking this study very seriously and is incorporating its findings in EPA's ongoing evaluation of the organophosphate pesticides, along with additional health data. EPA has completed a comprehensive reevaluation of all the organophosphate pesticides, and one of the outcomes of this process was the elimination of nearly all residential uses of organophosphate pesticides as well as some food uses to reduce risks to children. Data used in the Pediatrics study, from 2000-2004, would have been generated while these OP uses were being phased out and, thus, would not have reflected the new restrictions imposed by EPA.

Overall, the Agency agrees with the authors' conclusion that the data do not currently prove that organophosphates cause ADHD and that there are limitations in the organophosphate exposure assessment through the use of a single metabolite from a single spot urine sample. To determine whether a causal relationship exists between pesticides, including organophosphates, and health effects, the Agency is collaborating with various agencies of the National Institutes of Health and the Centers for Disease Control and Prevention in sponsoring the National Children's Study (NCS), a prospective study of the sort recommended by the authors.

EPA recommends that consumers who want to reduce their exposure to pesticides use common sense pest control methods that remove sources of food, water, and shelter for pests to reduce or eliminate pest problems before turning to pesticides. Always read and carefully follow label directions before using any pesticide. In addition, washing and peeling fruits and vegetables and eating a varied diet, will also reduce potential pesticide exposure.

OP Reregistration and Registration Review:

Seventeen OP pesticides have been canceled since the beginning of the reregistration process, leaving 32 currently registered. Fifty-eight OP pesticide uses on foods commonly eaten by children were canceled or are being phased out. As a result, OP pesticide use on kids' foods decreased from approximately 28 million pounds of active ingredient to approximately 12 million pounds (a 57% reduction) between the mid-1990s and 2004. The Registration Review schedule for the OP pesticides has also been accelerated, with dockets opening in 2008 and 2009.

This should serve as a reminder to use any insecticide wisely and only when needed (e.g. insect pest at the economic threshold levels) this summer!

Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu

 

SUGARBEET ROOT MAGGOT FLIES: SOUTHERN RRV PEAKING, MORE TO COME UP NORTH

Root maggot degree-day (DD) accumulations have advanced considerably in the past week. Correspondingly, root maggot fly emergence is well underway and the insects are moving into sugarbeet fields. As of May 31, the highest fly activity has been observed in rural areas of the following communities: Glasston, Oakwood, St. Thomas, Ada, Auburn, Euclid, and Thompson. Moderate activity is also occurring near Crystal, Grafton, Baker, and Minto. For online viewing of up-to-date postings of fly counts throughout the Red River Valley, visit:

www.ndsu.edu/entomology/people/faculty/boetel/flycounts/

Peak fly activity can occur at any time after the accumulation of 600 DD; however, NDSU research indicates that peak occurs, on average, at 651 DD (about 2-3 days after 600). It is important to note that dry, warm weather (around 80 F), and calm to low-wind conditions are most conducive to fly activity. Flies remain relatively inactive in cool, rainy, or windy conditions. Figure 1 presents DD accumulations for the region as of June 1.


Figure 1.
Sugarbeet root maggot degree-day (DD) accumulations.

To access this information online, consult the new NDSU Root Maggot Model application on the NDAWN website at:

http://ndawn.ndsu.nodak.edu/sugarbeet-root-maggot.html

The forecast for frequent chances of breezy and rainy weather, coupled with high temperatures hovering in the low- to mid-70s for the next several days, suggests that the actual peak in fly activity could take place in the few days. This makes forecasting a precise peak date difficult.

Activity is likely to peak in the southern Red River Valley between June 2-4, but there is potential for activity to continue in that area for a few more days. Significant increases in fly numbers are expected for the central and northern Valley during the next several days. Fly activity is forecast to occurr between June 6 and 8 for the central Valley, and between June 8 and 10 for the northern Valley.

Fly emergence and movement into beet fields can be accelerated quickly following a major increase in air temperatures. Growers in high-risk areas for SBRM infestation should consider applying a postemergence insecticide, especially if a low or moderate rate of an at-plant soil insecticide was applied.

Table 1 presents target DD accumulations for making region-specific postemergence insecticide applications. The recommendations are also based on whether a granular or liquid insecticide will be used.

Table 1. Area-specific suggested timing to apply postemergence liquid or granular insecticides for SBRM management in the Red River Valley.

Area

Target DD for Insecticide Applications*

Liquid Insecticide

Granular Insecticide

Northern RRV

590-620

440-550

Central RRV

585-615

410-545

Southern RRV

580-610

400-540

For growers in southern areas of the Valley (Hillsboro/Ada and southward) liquid insecticide applications are the best postemergence option at this point if they have observed high fly activity, or if they are at moderate to high risk of damaging infestations.

Growers in the more northerly locations (Grand Forks and farther north) still have time to apply a granular postemergence material, but it should be applied in the next few days. Otherwise, if planning on a liquid application, they should plan to apply them within 3 days of the expected peak (before peak is best). This should control both adults and larvae.

Another option is to treat infestations exceeding 0.5 SBRM flies per plant (1 per 2 plants) immediately with a liquid insecticide application at its labeled rate, even if the area has not reached the suggested target DD for treatment timing. Monitor such fields closely for several days after the application, and repeat if counts return to the 0.5-fly per plant level.

For more guidance on postemergence control strategies, consult the "Insect Control" section of the 2010 Sugarbeet Production Guide or the "Sugarbeet Insects" section of 2010 Field Crop Insect Management Recommendations. Online versions of these publications are located at:

www.sbreb.org/Production/production.htm

and

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

Mark Boetel
Research & Extension Entomologist
mark.boetel@ndsu.edu


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