Entomology Logo


ISSUE 5   June 11, 2009

CROPLAND GRASSHOPPERS EMERGING

The beginning of bloom in the common lilac (Fig. 1) serves as an indicator of when grasshopper hatch is underway. On average, 10 days after common lilac are flowering 75% of the grasshoppers are first stage nymphs and 25% are second stage nymphs. Earlier hatching and faster development is also expected on southern-facing slopes.


Figure 1.  Common lilac blooming.

So, it’s time to start scouting ditches and field edges for grasshopper nymphs (young hoppers) for the next few weeks. Young grasshoppers (Fig. 2) are tiny, about the size of a wheat kernel. Crop injury consists of leaf stripping and defoliation (cupping by first instar nymphs). Grasshoppers are more easily and economically controlled while they are in the nymph stage and still near hatching sites, such as roadsides and fence rows. Action thresholds for nymphs are: 50-75 nymphs per square yard in field margin, and 30-45 nymphs per square yard in field. Insecticides registered in North Dakota for grasshopper control in non-crop areas used for grazing or haying are carbaryl (Sevin), diflubenzuron (Dimilin 2L), malathion, and zeta-cypermethrin (Mustang Max EC). Insecticides registered in non-crop areas (NOT for grazing or haying) in North Dakota are acephate (Orthene, Address, Acephate 75%), esfenvalerate (Asana XL), gamma-cyhalothrin (Proaxis) and lambda-cyhalothrin (Warrior, Lambda–Cy EC). Please consult the 2009 Field Crop Insect Management Guide for more information on insecticides for grasshopper control on specific field crops.

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


Figure 2.  Nymph of two-striped grasshopper (photo by J. Fauske)

So far, this spring has been cool and wet. A cool spring prevents grasshoppers from premature hatch. However, the wet weather often increases grasshopper mortality, especially during heavy rains which can drown young grasshoppers. If cloudy, wet weather continues, naturally occurring entomopathogens that attack grasshoppers will be favored. One naturally-occurring fungal disease is called Entomophaga grylli or "Summit disease." It is easy to observe in the field, particularly later in the summer, because grasshoppers crawl up to the top of the plant and die with their heads pointing upwards and legs wrapped tightly around the stalks.

 

BLACK GRASS BUG ALERT IN GRASS CROPS IN SOUTHWESTERN NORTH DAKOTA

Black grass bugs (Hemiptera: Miridae) have been causing problems in CRP and pastures in Adams and Bowman counties in southwestern North Dakota. In some cases with heavy infestations, black grass bugs have moved into adjacent wheat and barley fields. These bugs have been identified as Labops hesperius Uhler (P. Beauzay, NDSU Extension Entomology).

Black grass bugs feed on a variety of grasses (crested wheat grass, brome grass, bluegrass, orchardgrass) and field crops (wheat, barley, rye, oats). Crested wheat grass is the most preferred grass. Adults and nymphs feed with piercing-sucking mouthparts and extracting the green (chlorophyll) tissue from plants, resulting in white spots and blotches on plant foliage (Fig. 3). Heavily infested plants can appear frosted. Small black spots of excrement covering plants are also symptoms of heavy feeding activity.

Black grass bugs have three life stages (egg, nymph and adult) and one generation a year. They overwinter in the egg stage in stems of host grasses. Eggs hatch in the spring and it takes 4-5 weeks to complete their life cycle to the adult stage. Adults (Fig. 4) are active feeders and females lay eggs into dry stems for 5-6 weeks. Females do not disperse far as they do not have fully developed wings.

Monocultures of grasses are preferred by black grass bug, and planting a polyculture can reduce feeding damage from black grass bug. During an outbreak year, heavy feeding damage can reduce yield, plant height and seed head production, especially during dry years. Plants can eventually recover if there is adequate moisture for plant growth. Black grass bugs can also affect forage grass quality by reducing crude protein and increasing acid content. Damaged leaves seem to repel cattle by making the grass unpalatable.

Insecticide control is typically not recommended in CRP, rangeland or pasture for lack grass bug, unless the grass is being grown for seed production. There is no economic threshold that has been developed for black grass bug. However, populations that exceed 1,000 bugs/ sq. ft. can cause host plant death. One well-timed insecticide application targeting the nymphs and adult females prior to egg laying can easily control black grass bug populations. Some insecticides registered in North Dakota for control of black grass bug in rangeland grasses used for grazing or haying are carbaryl (Sevin), malathion, and zeta-cypermethrin (Mustang Max). Some insecticides registered in non-crop areas (NOT for grazing or haying) in North Dakota are acephate (Orthene), and lambda-cyhalothrin (Warrior, Lambda–Cy EC). Insecticides will kill the adults and nymphs, but not eggs in stems. It is important to remember that black grass bug control with insecticides is typically not practical or economical in rangeland or pasture. Mowing, haying and grazing of grasses in late fall or early spring is recommended to reduce the number of egg laying sites and eggs. Black grass bugs will move into small grain crops like wheat that are adjacent to infested grassy areas. Typically, only the field edges of the wheat are infested. Wheat can sustain quite a bit of black grass bug feeding injury without significant yield losses, unless the flag leaf is severely damaged or the wheat is stressed by drought, lack of fertility or other pests. Lambda-cyhalothrin (Warrior II) and zeta-cypermethrin (Mustang Max – wheat ONLY) will control black grass bug in wheat and barley.

Note: Mention of any trade names does not imply endorsement of one product over another nor discrimination against any product by the North Dakota State University Extension Service or the author.

Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu

 

SUGARBEET ROOT MAGGOT: WHERE ARE ALL THE FLIES?

Sugarbeet root maggot (SBRM) flies are being monitored this year in a collaborative project between NDSU Entomology, American Crystal Sugar Company, the MinnDak Farmers Cooperative, and the Pembina County (ND) Extension office. The trap line, consisting of 41 sites, is arranged in a grid pattern that runs northward on both North Dakota and Minnesota sides of the Red River from Cass and Clay counties to near the US/Canadian border. In an average year, a significant amount of SBRM emergence usually occurs during the first week of June. Thus far, no flies have been detected since monitoring began on May 29.

As suggested in last week’s Crop & Pest Report, SBRM flies in the Red River Valley are expected to emerge abnormally late this year due to the persistent unseasonably cool temperatures that have characterized this spring.

Each year, the NDSU root maggot development model is used to monitor air degree-day (DD) accumulations and predict peak fly activity in current-year sugarbeet fields. Peak fly occurs on the first warm (80 degrees Fahrenheit or above), dry, low-wind (10 mph or less) day following the accumulation of 600 air DD. The past week did not produce adequate temperatures to advance development significantly.

Current DD accumulations and a long-range forecast for peak fly activity at representative locations throughout the Red River Valley are presented in the following table:

Degree-day (DD) accumulations for sugarbeet root maggot development as of June 9, 2009

Site

Soil temperature

Air DD1

Long-range forecast for Peak Fly2

Fargo

55

398

June 23 + 1st 80° day

Hillsboro

56

366

June 25 + 1st 80° day

Grand Forks

54

336

June 27 + 1st 80° day

Grafton

54

272

July 2 + 1st 80° day

Cavalier

56

262

July 3 + 1st 80° day

Raw data provided by the North Dakota Agricultural Weather Network (NDAWN).
1Peak fly activity in current-year beet fields; peak occurs after 600 air DD.
2Preliminary, long-range forecast – could vary substantially with departure from normal DD accumulations during next 3 weeks.

It should be noted that this year’s unusually cool spring will probably test the limits of the NDSU model because it has not been used on such exceptionally low rates of DD accumulations. In the past 30+ years of monitoring, peak fly has not occurred this late at these sites. Weather conditions during the next few weeks will have a major influence on this year’s peak activity dates.

Postemergence additive control strategies could prove very important this year, given that many fields were planted much later than normal in some of the moderate- to high-risk areas for damaging SBRM populations. Also of concern is the fact that a high percentage of fields were planted using seed treated with Poncho Beta insecticide. Additive postemergence insecticide applications are strongly advised in late-planted fields and/or those treated with Poncho Beta in SBRM problem areas. Poncho Beta should not be relied on for stand-alone protection in such areas.

Growers in areas of moderate to high risk of damaging maggot infestations should be vigilant about watching for potential flare-ups in fly activity, and plan on applying an additive postemergence insecticide to ensure adequate protection of their crop.

If a granular insecticide is preferred for postemergence control, apply the material between 5 and 14 days before anticipated peak fly activity. If a liquid insecticide will be used, make applications between 3-4 days before or within 3 days after peak. NDSU research indicates that control can be optimized by splitting full rates of Lorsban 4E (and other chlorpyrifos-containing liquid materials labeled for use in sugarbeet) in to two applications: make one application a few days before anticipated peak fly and repeat it in about 7 days.

Watch for updates on the root maggot fly forecast and for recommendations for postemergence insecticide application timing in future issues of the Crop & Pest Report. Detailed information can also be found in the "Insect Control" section of the 2009 Sugarbeet Production Guide or the "Sugarbeet Insects" section of 2009 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


NDSU Crop and Pest Report Home buttonTop of Page buttonTable of Contents buttonPrevious buttonNext button