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ISSUE 6   June 19, 2008

ALFALFA WEEVILS SCOUTING AND GROWING DEGREE DAY MAP

Field scouting for alfalfa weevil is initiated at 300 Growing Degree Days (GDD) using a base of 48 degrees F (see GDD map). Maximum feeding injury will occur from 450 to 600 GDDs (2nd - 4th instar larvae). At greater than 600 growing degree days feeding normally stops and adults emerge. This will occur usually during the second cutting unless the first is taken late. One can access the insect growing degree days on NDAWN under applications and insects, then degree days.

Alfalfa weevil GDD map

Scout south-facing slopes or sandy knoll areas which warm up rapidly first. These areas will have early development of alfalfa weevil larvae. Scout fields by sampling 10 plants in 5 random locations (50 total plants) and walking in an M-shaped or similar pattern throughout the field. Small alfalfa weevil larvae are slate-colored. As larvae mature, their color changes to bright green with a white line running down their back and a black head capsule. Mature larvae are about th of an inch long (see photo).

Alfalfa weevil larva
Alfalfa weevil larva (photo courtesy Clemson Univ. -
USDA Coop Ext. Slide Series, Bugwood.org)

Management of weevil infested alfalfa stands depends on when the infestation occurs. If the infestation occurs relatively late, when the alfalfa has reached 20 to 25 inches in height, consider taking an early harvest. Small alfalfa weevil, those less than ¼ inch in length, will drop to the soil and generally die if the soil is dry. If the infestation occurs early, when alfalfa is 10 to 15 inches in height, insecticide treatment may be necessary. Insecticide treatment is recommended if two live larvae per stem occur at this stage and/or 35-40% of the plants are showing tip feeding. In general, if alfalfa is 7-10 days out from harvest and 35-40% tip feeding is present, an insecticide treatment is recommended. If following the first harvest, your scouting shows 8 or more larvae per square foot or larvae are suppressing regrowth, insecticide treatment is recommended. North Dakota insecticide recommendations for alfalfa are listed at the following website:

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

Remember to check the preharvest interval as these restrictions vary according to the insecticide used and the rate applied. Other factors to consider when selecting an insecticide is its price, potential hazards to honey bees and whether or not it is a restricted use insecticide.

 

CUTWORM ACTIVITY CONTINUES!

Field reports indicate that cutworms are still a problem in many agricultural crops, especially in north central and northwestern regions of North Dakota (see sunflower damaged field photograph). Early season cutworms, like dingy cutworms, should be completing their life cycle and starting to pupate (non-feeding, resting stage). Check the size of the cutworm larvae to see if it is mature (about >1 inch). If young cutworm larvae (<½ inch) and newly injured plants are not present, there would be no economic benefit to treating the field with an insecticide. Some of the late-season cutworms that may be active now include red-backed cutworm (see photograph), darksided cutworm and variegated cutworm. These late season cutworms overwinter as eggs where as the early season cutworms overwinter as partially mature larvae, which resume feeding in spring. This year scouting is a must until early July with the late season.

Damaged sunflower field
Sunflower field damaged by cutworms (in front half of photo)

Red-backed cutworms
Red-backed cutworms (left to right - adult moth, 2 pupae, and 2 larvae)

 

SOYBEAN APHID UPDATE

In the Red River Valley, many ladybird beetles, namely the Asian multicolored lady beetle, Harmonia axyridis (see photograph of adult and larva), have been observed in tree rows with buckthorn, the overwintering host of soybean aphids. These predators devour aphid eggs, nymphs and adults. They play an important role in reducing local populations of soybean aphids, especially early in the growing season. Harmonia axyridis is easy to identify from its false "eyes"-- two white-shaped markings and a distinctive black ‘M’ behind the head. In color, the insects range from black to mustard to red, with zero to many spots. A common color is red with 16 or more black spots.

Harmonia axyridis adult
Harmonia axyridis adult (photo courtesy Scott Bauer,
USDA Ag. Res. Service, Bugwood.org)

Harmonia axyridis larva
Harmonia axyridis larva (photo courtesy D. Cappaert,
Michigan State Univ., Bugwood.org)

With the cool weather conditions, soybean emergence has been delayed in North Dakota and Minnesota this year. Research from the University of Minnesota indicates the soybean aphid has the ability to "recolonize" buckthorn if soybean is not available (source: D. Ragsdale). Additional soybean aphid information will be posted in upcoming Crop & Pest Reports.

 

INSECT MIGRATION RISK FORECAST LOW - SO FAR

The Insect Migration Risk Forecast (IMRF) from Northern Illinois University by M. Sandstrom and D. Changnon has predicted LOW risk of insect migration into the northern areas of the U.S. The reason is the recent northerly and northwesterly wind flows, which has slowed the "insect pump" from the southern states into North Dakota. The major insect pests that migrate into North Dakota include: cereal aphids, diamondback moth, potato leafhopper and aster leafhopper. The IMRF is available at the following website:

http://www.agweather.niu.edu/IMRFForecast.html

 

WHEAT STEM MAGGOT UPDATE

The first adult wheat stem maggot flies have been collected using sweep nets in the Fargo, Page, Regent, New Leipzig, Hettinger, Makoti and Roseglen areas this week. Very few flies (<10 flies per 100 sweeps) have been captured, so we assume that this is the beginning of its emergence period. Future field observations will be posted in upcoming Crop & Pest Reports.

Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu

 

TICK PROBLEMS FOR LIVESTOCK IN PASTURES

Tick Biology: The most common ticks affecting livestock in our area are ticks in the genus Dermacentor. Three species are found in North Dakota: American dog tick (D. variabilis), Rocky Mountain wood tick (D. andersoni), and winter tick (D. albipictus). Of these, American dog tick is the most common species.

Dermacentor ticks are blood-feeding external parasites of several mammal species, including humans, dogs, cattle, and horses. They have piercing-sucking mouthparts that are inserted through the skin of their host and into vascular tissue. Once engorged with a blood meal, a tick will drop off its host to mate, lay eggs, or continue development. The life cycle of ticks is comprised of four distinct developmental stages: eggs, larvae, nymphs, and adults. Adult males and females require several days of feeding after which the male copulates with one or several females and dies. Adult females drop to the ground after mating and begin laying eggs. Females die after laying eggs. Eggs are laid on the ground in masses of over 1,000 eggs and require several days to develop depending on environmental conditions. Emerging larvae have six legs and may crawl up on vegetation and wait for a suitable host to pass by (see photograph). Larvae attach to a host, and after a blood meal drop to the ground to molt into eight-legged nymphs. Again, nymphs crawl up on vegetation and wait for a host. Engorged nymphs may rest for long periods of time before molting into the adult stage. There is probably one generation per year for American dog tick and winter tick in North Dakota. Rocky Mountain tick has a two to three year life cycle. These ticks probably overwinter as larvae or nymphs.

American dog tick
American dog tick questing (photo courtesy
Jim Occi, BugPics, Bugwood.org)

Adult male Dermecentor ticks are recognized by a shiny brown dorsal surface with white mottling. Females are recognized by having a white thorax dorsally. Typically, males do not engorge themselves to the degree that females do. Engorged ticks may loose their basic coloration and appear gray.

Ticks are attracted to the scent of animals and are most commonly found along game trails, livestock paths, and fence rows and roadways. This is important for tick control as range or pasture treatments should be focused on these areas.

Tick Control: Control of ticks and tick-borne diseases has been accomplished primarily with pesticides called acaricides to kill ticks. Pesticides can be applied to the pasture and/or directly to the animals, depending on the chemical.

Pasture treatments: Carbaryl (Sevin) may be used to treat open areas and the perimeter. Pasture may be harvested or grazed the same day as treatment. Some of the pyrethroids registered for tick control include: Cyfluthrin (Tempo 20WP or 2L), bifenthrin (Talstar) and esfenvalerate (Asana XL), and may be used only as a perimeter spray in noncropland areas where livestock do not graze. Treat in spring when temperatures begin to exceed 60 degrees F. Treatment may need to be repeated in the fall. Adhere to grazing and preharvest restrictions as stated on the label.

Direct treatment to livestock: Permethrin is one of the common pesticides registered for direct treatment to the animals. There are a variety of procedures for treating animals with acaricides including dipping cattle, dusts, systemic injection systems and plastic collars. Regardless of the treatment method used, producers need to know and follow proper application procedures to derive maximum benefit. The development of tick resistance to acaricides is a major concern and research on new products is needed to overcome resistance to compounds already in use.

Alternative pest management methods: Tick survival requires humid microhabitats covered by vegetation, leaf litter, soil and other natural materials, or in the nests, burrows, and other cavities used by their hosts. As a result, ticks often do not come into direct contact with these toxicants. For an acaricide to be effective in killing ticks, it must reach the tick as vapors or by contact when the ticks move about while seeking hosts. Alternative pest management methods include habitat modification - burning or clearing of vegetation, or host removal (e.g. removal of deer by hunting or deer exclusion fences). Burning or clearing vegetation removes the dense cover under which ticks shelter, and reduces ground-level humidity making the habitat unsuitable for tick survival. Effective tick control should include an integrated pasture management approach – rotational grazing, selected use of acaricides and alternative methods.

Patrick Beauzay
Extension Entomology Research Specialist
patrick.beauzay@ndsu.edu

Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu

 

SUGARBEET ROOT MAGGOT: MAJOR FLY ACTIVITY SURGE LIKELY OVER WEEKEND

Sugarbeet root maggot (SBRM) fly counts from sticky stakes have remained low throughout the Red River Valley (RRV) during the past several days, but this week’s more "normal" June weather should quickly change that scenario. Significant increases in degree-day (DD) accumulations have occurred during the past few days, so a dramatic, sharp increase in root maggot fly activity is expexted.

Peak fly activity usually occurs shortly after the accumulation of 600 DD. As indicated in Table 1, much of the RRV reached that level as of June 18. The northern Valley is likely to reach 600 units by June 21. Typically, the actual peak usually lags 1-3 days after reaching 600. Fly activity is expected to peak around June 20 or 21 in central and southern portions of the RRV, whereas the high-risk areas of northeastern ND are likely to see peak fly around June 23. Warm (around 80 F), dry weather and calm to low-wind conditions are most conducive to fly activity, so rainy or windy weather could cause slight delays the actual peak date.

Table 1. Degree-day (DD) accumulations and predicted peak activity dates for sugarbeet root maggot flies in Red River Valley

Site

Degree Day units (as of June 18)

Peak fly activity forecast*

Baker, MN

608

June 21

Ada, MN

610

June 21

Grand Forks, ND

621

June 20

St. Thomas, ND

561

June 23

*Peak fly activity in beets is most likely on the first calm or light-wind and 80 F day, after the required 600 air DD are accumulated.

Fields in high-risk areas may require the application of a postemergence rescue insecticide, especially if a low or moderate rate of a planting-time insecticide was used on the crop. Rescue insecticide applications are also recommended if a hotspot of SBRM fly activity erupts in a given field. Liquid insecticides are going to be the best option at this time because most infestations are so close to peaking. Postemergence liquid insecticides should be applied within 3 days of the expected peak, and applications made before peak work best. This will provide control of both adults and larvae.

WHAT ABOUT TANKMIXING MY INSECTICIDE WITH AN HERBICIDE? This approach certainly has practical value, because it can save the producer input costs by combining two applications into one pass across the field. NDSU research indicates that crop safety and effective weed and insect control can be achieved by tankmixing a microrate herbicide combination with an insecticide for SBRM control. Insecticides tested in this scenario have included Lorsban 4E and Mustang Max. FMC Corporation has endorsed the use of Mustang Max/glyphosate mixtures with a 2(ee) recommendation. Limited testing has also been done on tankmixing glyphosate with Lorsban 4E, and no crop injury or loss in insect control has been observed. However, it must be noted that glyphosate labels do NOT endorse glyphosate/insecticide combinations for use in sugarbeet. Therefore, growers choosing to mix their preferred SBRM foliar insecticide with glyphosate for use in sugarbeet assume all liability for any potential control failures or crop losses associated with such applications.

For more guidance on the sugarbeet root maggot forecast or insect control strategies, consult the "Insect Control" section of the 2008 Sugarbeet Production Guide or the "Sugarbeet Insects" section of 2008 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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