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ISSUE 2   May 20, 2010

WATCH FOR EARLY SEASON INSECTS

Wireworms

Wireworms are larvae of click beetles (family Elateridae). When soil temperatures reach 50 to 55 F during the spring, larvae and adults move nearer the soil surface. During the summer months, larvae move deeper into the soil where temperature and moisture conditions are more favorable. Wireworm larvae (Fig. 1) are hard, smooth, slender larvae ranging from ľ to 1 inch in length when mature. They are yellowish white to coppery in color, with three pairs of small, thin legs behind the head.


Figure 1.
Wireworm larva (M. Boetel, NDSU)

The last body segment is forked or notched. Adult wireworms (Fig. 2) are bullet-shaped, hard-shelled beetles that are brown to black and about 0.5 to 1 inch long. The common name "click beetle" is derived from the clicking sound that the insect makes when attempting to right itself after landing on its back.


Figure 2.
Click beetles (wireworm adults)
(S. Brown, Univ. of Georgia, Bugwood.org)

Wireworms usually take three to four years to develop from egg to adult. Most of this time is spent as larvae, the life stage injurious to crops. Wireworm infestations are more likely to develop where grasses, including grain crops, are grown the previous year. Wireworms damage crops by feeding on germinating seeds, young seedlings or roots. Damaged plants soon wilt and die, resulting in thin stands. In a heavy infestation, bare spots may appear in the field and reseeding is necessary.

Management: Decisions to use insecticides for wireworm management must be made prior to planting. No rescue treatments are available for controlling wireworms after planting. Producers have no easy way to determine the severity of infestation without sampling the soil. Infestations vary from year to year. Considerable variation may occur both within and between fields. Sometimes the past history of a field is a good indicator, especially if wireworms have been a problem in previous seasons.

In the spring, the sampling procedure involves digging and sifting a soil sample for the presence of wireworms. When digging soil samples, 12 or more wireworms in 50 12-inch by 12-inch samples are likely to result in damage to crop. In the fall, a soil bait station trap of corn-wheat seed mixture can be used to attract wireworms. If the average density is greater than one wireworm per bait station, the risk of crop injury is high and an insecticide seed treatment or soil insecticide should be used at planting to protect the crop. If no wireworms are found in the traps, risk of injury is low. See NDSU Extension publication on wireworms for more information:

www.ag.ndsu.edu/pubs/plantsci/pests/e188-1.htm#Sampling

Cutworms

Adult cutworms are moths (Fig. 3) that belong to the family Noctuidae. Larvae are typically dark gray, brown or black and up to 2 inches long (Fig. 4).


Figure 3.
Redbacked cutworm adult (G. Fauske, NDSU)


Figure 4.
Redbacked cutworm larva (J. Knodel, NDSU)

Cutworm damage is caused by larval feeding and normally consists of seedlings being cut off below or above the soil surface. Young leaves also may be severely chewed from cutworms climbing up to feed on the plant foliage. Most cutworms feed at night. During the daytime, cutworms are usually found just beneath the soil surface near the base of recently damaged plants. Wilted or dead plants frequently indicate the presence of cutworms. Cut plants may dry and blow away, leaving bare patches in the field as evidence of cutworm infestations.

Management: Sampling should begin as soon as plants emerge, and fields should be checked at least twice per week until approximately mid-June. Stand reduction is determined by examining 100 plants per five sampling sites for a total of 500 plants. A trowel or similar tool should be used to dig around damaged plants to determine if cutworms are present, since missing plants in a row does not necessarily indicate cutworm damage (gaps may be caused by a defective planter, poor germination, rodents or birds). The size of the cutworm larvae should also be estimated. Small larvae pose the greatest potential for damage as they still have to feed and grow. Post-emergent treatment with an insecticide provides quick control of surface feeding cutworms. Best results occur if insecticide applications are made at night. Seed treated with an insecticide seed treatment will only provide suppression of cutworm activity. For specific economic thresholds and insecticides registered for cutworm control by crop, please consult the 2010 North Dakota Field Crop Insect Management Guide:

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

Grasshoppers

Each summer, USDA-APHIS-PPQ personnel conduct an adult grasshopper surveys on rangeland during the late summer throughout the western states. The data collected from these surveys is used to forecast areas of rangeland that may have damaging populations of grasshoppers the following growing season. The rangeland grasshopper hazard map (Fig. 5) indicates that North Dakota is at lower risk than other states like Montana, Wyoming, South Dakota and Nebraska.


Figure 5.

Areas in red indicate the highest threat, followed by orange, green and blue (lowest threat). The highest populations of grasshoppers in North Dakota were found in the southwestern and south central regions. For more information, please see: www.sidney.ars.usda.gov/grasshopper/Extras/index.htm

The weather and availability of food sources will determine how bad the grasshopper threat will become this year. Cool, wet weather increases disease occurrence, grasshopper nymph mortality and delays development of grasshoppers. These factors reduce the overall population while the grass or crop continues to outgrow any grasshopper injury. Dry and warm weather will favor grasshopper development and limits grass or crop growth, thus making any grasshopper injury more important to manage. Vigorous, healthy grass or crop development early in the season reduces grasshopper problems. The cool wet weather during the last two weeks may have caused some grasshopper mortality, since the young nymphs are very susceptible to cool, wet weather.

Grasshopper Threshold: In North Dakota, begin scouting for grasshoppers in late April to early May. Peak emergence occurs about mid-June. In most crops (except lentils), grasshopper control is advised whenever 50 or more small nymphs per square yard can be found in adjacent, non-crop areas, or when 30 or more nymphs per square yard can be found within the field. When 20 or more adults per square yard are found in field margins or 8 to 14 adults per square yard are occurring in the crop, treatment would be justified. Since it is difficult to estimate the number of grasshoppers per square yard when population densities are high, pest managers can use four 180-degree sweeps with a 15-inch sweep net, which is equivalent to the number of adult (or nymph) grasshoppers per square yard.

Many of the grasshopper infestations will be the heaviest on the field margins. Treating these areas may lessen the total numbers of grasshoppers successfully entering a field.

 

BLACK FLIES EMERGING AND BITING!

Black flies (Fig. 6) are being reported in from Cass, Grand Forks and Pembina Counties this week.


Figure 6.
Black fly (www.epa.gov/bioiweb1.html/blackflies.html)

As I write this article, Iím suffering from several bites myself! Black files are pests of humans and animals and most complaints are in May to June in North Dakota. They are commonly called buffalo or turkey gnats and belong to the insect family Simuliidae. The immature stages (eggs, larvae, and pupae) develop in moving water and will die within 10-75 hrs without moving water to provide oxygen and food. Only the females bite; males feed on plants. Bites can be painful and cause dermatitis and itching for several days. Black flies are attracted to dark colors so wear lighter colored clothing. Unlike mosquitoes, black flies only bite during the day and prefer low winds. Losses to livestock and poultry are difficult to estimate, but decreased milk, beef and egg production are common when high populations of black flies are present. Flies live for about three weeks.

There is little that the homeowner can do to control black flies, except to avoid outdoor activities during peak black fly season. Using protective repellents have only some relief depending on species of fly, temperature, humidity and time of day. Fine mesh screening can be used over hats to protect the face. The best method of control is to reduce the number of breeding areas. Removal of vegetation and objects in streams will help minimize the number of larvae, since larvae attach to submerged objects during development. Temporary damming of water can also lower populations as immature stages require running water to survive. Any insecticide used as a fogger provides only temporary relief as black flies can fly 7-10 miles or can be blown by the wind even further. Treatment of streams is only effective if timed correctly and on a large scale community effort by local government programs. A bacterial biopesticide, Bacillus thuringiensis var. israelensis, is a larvicide that is nontoxic to nontarget organisms such as fish, birds, etc. and can be applied to streams by aircraft.

 

FUN INSECT FACTS

What is this large insect is being found near lights in parking lots or warehouses?


Figure 7.
Giant water bug (E. Manigault,
Clemson Univ., Bugwood.org)

This is the giant water bug! It belongs to the order Hemiptera and family Belostomatidae. Giant water bugs are one of the largest insect in the U.S. ranging from 1.5 to 4 inches in length depending on the species. It is sometimes mistaken for a cockroach or a beetle. These bugs live in aquatic habitat like ponds or slow-moving streams. Giant water bugs are predaceous with large raptorial forelegs. They lie and wait motionless for their prey and then suddenly grab it piercing the body of the prey with its pointed beak-like mouthparts. Enzymes are injected into the prey that dissolves the body tissues, and then the bug will suck up the liquids. They eat small aquatic invertebrates and vertebrates such as tadpoles, salamanders

Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu

 

SUGARBEET ROOT MAGGOT MODEL: NEW ON NDAWN

A new sugarbeet root maggot development model has been developed at NDSU. The model is used to monitor degree-day (DD) accumulations and predict peak fly activity in current-year sugarbeet fields. It is based a correlation of observed peak fly dates with DD accumulations at over 120 monitoring sites in the Red River Valley during the past 15 years. Peak fly activity usually occurs on the first warm (80 degrees Fahrenheit or above), dry, low-wind (10 mph or less) day that coincides with or follows the accumulation of 651 air DD. The model application is located on the NDAWN website at:

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

Root maggot development is following a slightly more "normal" pattern this year. Overwintered SBRM larvae observed in recent surveys in the St. Thomas area indicate that they are beginning to molt into pupae. After pupation, they will take several days before emerging as adults and searching for sugarbeet fields in which to lay eggs. Weather conditions during the next couple of weeks will have a major influence on the exact date of peak activity. Cold, windy, or rainy weather will delay the actual peak, even if adequate DD units have been accumulated for adults to emerge from soil. The first-emerging flies should be observed soon, and there may even be a very small number beginning to become active. However, peak fly activity across the Red River Valley is still likely to be at least 3 or 4 weeks away for most sites.

 

POSTEMERGENCE CONTROL OF SUGARBEET ROOT MAGGOT

The 2010 risk map for sugarbeet root maggot infestations in the Valley is presented in Figure 1. Growers in areas of moderate to high risk of damaging maggot infestations should be vigilant at monitoring fly activity in their fields, and plan on applying an additive postemergence insecticide to ensure adequate control. Fields in these areas that are protected by Poncho Beta insecticidal seed treatment are especially likely to need additive protection because Poncho Beta is a moderate-performing product for sugarbeet root maggot control. Poncho Beta should not be relied on for stand-alone protection in such areas.


Figure 1.
2010 Forecast map for sugarbeet
root maggot populations in the Red River
Valley (based on fly activity and root maggot
feeding injury ratings at 40 monitoring sites
during the preceding growing season)

If a granular insecticide is preferred for postemergence control, apply it between 5 and 14 days before peak fly activity. The FIRST postemergence granular insecticide applications should NOT be applied before May 24. If a liquid insecticide will be used, make applications between 3-4 days before or within 3 days after peak fly. 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 3 or 4 days before anticipated peak fly and repeat it about 7 days later. More detailed information can be found in 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:

http://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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