Contents:

• Life Cycle
• Damage
• Yield Losses
• Methods for Tracking Seasonal Activity
• Cultural Controls
• Natural Controls

• When to Treat

  First Generation

  Second Generation

• Methods of Insecticide Application
• Pest Management Safety
• Ordering Supplies

LIFE CYCLE

First Generation

Second Generation

DAMAGE

YIELD LOSSES

1) Plant stage. Percentage yield loss differs depending on the plant growth stage at the time the damage occurs. Cavity formation by the first generation borer usually occurs before tassel emergence resulting in approximately 5 percent yield loss per borer per plant. Yield losses (per borer) from second generation larvae vary widely because cavity formation may occur over several weeks, and rapid physiological changes occur as the ear is approaching maximum size and physiological maturity. The average value of about 5 percent yield loss per borer per plant appears appropriate until shortly after pollen shed. As the ear advances from the blister stage to physiological maturity, the yield reduction per borer rapidly decreases.

3) Hybrid. Hybrids vary in their response to feeding by the European corn borer. Resistance to whorl, and sheath and collar feeding, is available in some commercial hybrids. Some varieties have the genetic capacity to yield better than others in the presence of borer damage. Relative stalk strength, firmness of the plant rind, and shank strength influence borer establishment on the plant, the amount of stalk breakage and the capacity for ear retention in the event of a corn borer infestation. Several seed corn companies are currently marketing Bt transgenic corn. Bt-corn hybrids produce an insecticidal protein derived from the bacterium Bacillus thuringiensis, commonly called Bt. These Bt hybrids provide a very high degree of control against damage by the first generation borer. Control of second generation European corn borer larvae varies from moderate to excellent depending on the hybrid and the degree and location of expression of the insecticidal trait. In all cases however, control should either compare favorably or significantly exceed that which could be achieved be a conventional insecticide application. Follow all resistance management recommendations when planting Bt corn.

METHODS FOR TRACKING SEASONAL ACTIVITY

Light traps attract insects to a light source, and then trap them in a receptacle containing a killing agent. Trapped insects should be counted on a regular basis (daily, or several times a week). A fluorescent 15-watt ultraviolet (black light) lamp commonly serves as the light source. The disadvantage of light traps is that several species of flying insects are attracted to the light source and therefore the nightly catch needs significant sorting to assess ECB moth numbers. (See the end of this document for sources of light traps).

European corn borer pheromone traps contain a substance that mimics a part of the chemical communication system between male and female corn borer moths. Specifically, it mimics the chemical emitted by those females that are receptive to mating. Only male ECB moths are attracted and captured and therefore no sorting is required and counting is relatively quick. This lure (Iowa type) is commercially available and is used within a rigid paper trap coated with a sticky substance that retains the attracted insects. Trap catches are monitored on a regular basis. At present, little information is available regarding the interpretation and use of pheromone traps for surveying ECB. They have been used, however, to detect the initiation of moth flights. (See the end of this document for sources).

A third method uses temperature accumulations called degree days. Since temperature is a major regulator of borer development, accumulated temperature units (degree days, 50o F base temp.) can be used to predict the seasonal occurrence of the subsequent life stages following capture of the first moth of the season in pheromone or light traps (Figure 2). Degree-day accumulations not tied to the first moth capture are much less accurate in predicting corn borer development.

Computer software is available that runs on IBM and compatible computers equipped with at least one 5 1/4 inch floppy drive. The software contains a phenology model that predicts the egg-laying time of second brood (summer) moths based on the age distribution from a collection of the earlier first generation larvae (the management portion of the model will be discussed later). Degree-days for the phenology model may be based on either 30-year county averages (program default values) or local temperatures for the current year. This is the most accurate method to determine scouting times for second generation egg laying. Correctly identifying the larval stages or instars of the first generation larvae is important to the success of running the model.

A final method of tracking the seasonality of European corn borers relates to scouting efforts in the field for the life stages of the borer. Scouting individual fields is still the BEST way to assess ECB population progress and magnitude of infestation. A video tape on scouting for European corn borer is available for additional specific information in addition to the information stated elsewhere in this document.

CULTURAL CONTROLS

Variety selection. As previously noted, percentage survival of borers feeding on the corn plant varies with the corn hybrid. Some varieties of corn are resistant to first generation ECB larvae whorl feeding. In resistant hybrids, borers die shortly after feeding on plant whorl tissue although some "shot holing" may be noticed. Because the resistance factor causes death of the insect, it is called antibiosis and is largely attributed to a substance in the plant called DIMBOA. These hybrids maintain this resistance trait up to tassel emergence. Some varieties of corn may also express sheath and collar feeding resistance applicable against second generation borers. This resistance trait may be in addition to or apart from resistance to whorl feeding. As in whorl feeding resistance, borers die soon after feeding. There also is variability across hybrids in the plant's response in relation to stalk and ear shank strength, plant rind toughness and ear retention characteristics. These resistance traits are classified as tolerance.

Maturity group.The maturity group of the hybrid will dictate when the hybrid will flower and be most attractive to the egg-laying moth. An early maturity group hybrid flowering (tasseling and pollinating) before peak moth flight will have significantly fewer corn borers. Conversely, long season hybrids that pollinate during the summer moth flight, are particularly susceptible to borer establishment. Check with your seed corn representative for information on specific hybrids. Also see E.C. 105, "Nebraska Corn Performance Tests," published annually by the Nebraska Cooperative Extension Service and the Nebraska Agricultural Research Division. This publication includes information on the percentage of broken plants and percentage of dropped ears for the tested corn hybrids.

Planting date. Planting date is important because the height of the corn relative to surrounding corn during the first brood moth flight and the maturity of the plants relative to surrounding corn during second moth flight will helpdetermine the vulnerability of the hybrid to an ECB infestation. Moths of the first flight in June are most attracted to the taller corn, but will lay some eggs on shorter corn (2- to 4-leaf stage). Borer establishment will be poor in corn plants with less than six fully expanded leaves (whorl height approximately 10 inches). The second flight of moths emerging in late July and early August prefers to deposit eggs on corn at or near pollen shedding. If corn is planted late and/or a particularly long season variety is planted, the late maturation of that corn relative to surrounding corn may make it highly attractive to egg laying moths.

Early harvest. The longer corn remains in the field after maturity, the greater the amount of stalk lodging, breakage, and ear drop. This is especially true in fields heavily infested with ECB. Scout fields in the fall and make an assessment on potential harvest losses from stalk breakage and ear droppage. Then compare early harvest and drying expenses to potential losses if the corn is not harvested until an acceptable moisture level is reached.

NATURAL CONTROLS

Disease organisms. Two disease organisms are sometimes effective in reducing corn borers. One is a widespread fungus, Beauveria bassiana, that attacks and eventually kills the larvae. More than 50% of overwintering populations of borers can be killed in some years. The other, a protozoan organism, Nosema pyraustae, infects eggs, larvae, pupae, and adults. This results in fewer eggs being deposited and reduced larval survival.

Predators and parasites. Several birds feed on overwintering borers within the stalks, while lady beetle larvae and adults and lacewing larvae feed on eggs and newly hatched larvae. A native lady beetle Coleomegilla maculata , can be a significant predator of ECB egg masses. A tachinid fly, Lydella thompsoni, is a common and widespread parasite of ECB and has some success in biological control. Two wasps, Eriborus terebrans and Macrocentrus grandii parasitize 2nd to 4th-instar ECB larvae and are widespread in Nebraska. Another parasitic wasp, Sympiesis viridula, may also be present in Nebraska, but its impact is small during most years.

WHEN TO TREAT FOR ECB ON CORN

First Generation:

To make a decision on first generation borer treatment, the following information is needed:

1. Average percent damaged ("shot-holed") whorls in the field.
2. Average number of larvae per damaged plant.
3. Cost per acre of the insecticide and the application.
4. Anticipated yield in bushels per acre
5. Anticipated value of the grain ($ per bushel).
6. Estimated percentage control achieved by insecticide application.

Example:

Second Generation:

The management model progresses through a number of steps of a decision process leading toward a recommendation on the need for control. Research shows that this model is an oversimplification of the complex set of factors operating in the corn field. A more refined model is under development. However, the present model does include essential items of the costs of the insecticide application, the estimated final borer populations relative to plant stage, the value of yield loss associated with that population and the estimated percentage control to be achieved by the insecticide. It's accuracy is most limited by our estimation of the biological events of the ECB that need to be quantified to arrive at a final ECB larvae population that is used estimate yield loss.. These estimators must be our best judgments.

The following example is based on the computerized management model but without the significant benefit of the use of the phenology model predicting ovipositional patterns. It involves two separate steps:

1. calculating an economic threshold (ET) and
2. comparing the ET with the calculated Potential Pest Density (PPD).

To calculate the proportion of eggs already laid (PO), the following assumptions must be made; the egg-laying period is 20 days long and peaks 10 days after it begins, and the first egg mass is not found before 5% of egg laying is completed. For example, if the first egg mass is found on July 20, and you had been scouting on a 2-day schedule, the actual start of egg laying occurred 3 days earlier on July 17. The table below provides PO values for different points in the egg-laying period:

Example:

1. Calculating the economic threshold or ET:

CC = Estimated control costs (includes the cost of the insecticide and cost of application.

YL = The percentage estimated loss in yield per borer per plant. (Consult table 3 below).

MV = The estimated market value of the corn when you intend to sell it.

EY = The expected yield in bushels/acre.

PC = The percentage control expected if an insecticide is applied.

Therefore, based on this example, a potential pest density of 1.32 borers/plant is necessary to break even.

2. Calculating the potential population density or PPD:

SV = Average proportion of individuals surviving through the damaging stage. Use the conservative value of 0.20.

EM = Average number of eggs in each mass. Use the number 23.

MP = Average number of egg masses per plant based on scouting.

PO = Proportion of eggs already laid, based on a 20 day ovipositional period in each field (See Table 2).

Therefore since the potential pest density of 3.59 borers per plant exceeds the economic threshold of 1.32 borers per plant, it would be profitable to apply an insecticide.

The key to controlling second generation borers is to time applications when the first egg masses begin to hatch. Best control and economic return will be achieved when initial egg hatch coincides with reaching the economic threshold. As the plant matures beyond the blister stage, potential economicbenefits of a successful insecticide application rapidly decline.

There is uncertainty about the feasibility of multiple applications of insecticides to offset the extended ovipositional period of the moth during some years. Limited research indicates a well-timed single application is sufficient in most years. If other insect pests are present and or ECB moth population levels are high, liquid formulations are preferred over granules for second generation control because of their broader spectrum of activity, and the added advantage of obtaining some moth control.

BE ALERT FOR POSSIBLE BUILDUP OF SPIDER MITES AFTER INSECTICIDE APPLICATION.

METHODS OF INSECTICIDE APPLICATION

Liquid insecticides can be applied through center pivot irrigation systems (chemigation). In Nebraska, chemigation is regulated by the Nebraska Chemigation Act. Applicators must be certified chemigation applicators and all injection sites must be permitted. This method, while proven effective when compared with more conventional application techniques, requires proper equipment (including safety devices), an understanding of how to use it properly, and monitoring to ensure proper application, safety to others and to the environment. Proper equipment, procedures for calibration, and other instructions for application through center pivot systems is provided in two documents - "Applying Insecticides Through Center Pivots" (G84-703) and "Anti-pollution Devices for Applying Chemicals Through Irrigation Systems" (G73-43). Refer to product labels for specific instructions in handling and proper injection procedures, precautions, and restrictions.

Conventional ground sprayers, aircraft, or high clearance sprayers can be used for applying liquid insecticides. Excepting chemigation, liquids have not been effective against first generation borers because the water volume is not sufficient to carry the insecticide inside the plant whorl. High clearance sprayers or aircraft fitted with multiple nozzles to ensure thorough coverage of leaf axils and the ear zone can be used for control of second generation borers.

Recommended insecticides and rates of application can be found in the current edition of Extension Circular EC-1509, "Insect Management Guide for Nebraska Corn and Sorghum," available from your Nebraska Cooperative Extension office. Products based on the naturally occurring bacterium, Bacillus thuringiensis are effective against first generation corn borers and have advantages over other insecticides in terms of applicator safety, and reduced toxicity to insect predators and parasites, honeybees and wildlife. These products have not been as effective as synthetic insecticides when used for control of second generation corn borers.

PEST MANAGEMENT SAFETY

Insecticide Recommendations for First Generation European Corn Borer Control in Field Corn

ORDERING SUPPLIES

Light Traps:

O. B. Enterprises, Inc., 4585 Schneider Drive, Oregon WI 53575, 608-835-9416

Pheromone Traps:

(Scentry Wing traps with Iowa Strain ECB lure)

Ecogen, Inc., Scentry Division, 2005 Cabot Blvd. West, Langhorne PA 19047

Phone: 1-800-220-3326, or (215)-757-1590.

Great Lakes IPM, 10220 Church Road NE, Vestaburg, MI 48891

Phone: (517) 268-5693

European Corn Borer Phenology and Management Model:

Send orders with payment (payable to University of Nebraska) to Bob Wright,

University of Nebraska South Central Research & Extension Center.

Box 66, Clay Center, NE, 68933-0066. Or, contact Bob at (402) 762-4439.

Specify 3 1/2 or 5 1/4" disk size. $71.23 (includes sales tax, shipping and handling)

Videotape:

Insect Scouting in Corn, 26 min., VHS format; $29.95 + sales tax;

Send orders with payment (payable to University of Nebraska) to

Field Scouting, 104 ACB, UNL, Lincoln NE 68583-0816.