Plant Biotechnology: Current and Potential Impact

For Improving Pest Management In U.S. Agriculture

An Analysis of 40 Case Studies June 2002

Insect Resistant Field Corn (3)

Leonard P. Gianessi Cressida S. Silvers

Sujatha Sankula Janet E. Carpenter

National Center for Food and Agricultural Policy

1616 P Street, NW Washington, DC 20036 Phone: (202) 328-5048 Fax: (202) 328-5133

E-mail: ncfap@ncfap.org Website: www.ncfap.org

Financial support for this study was provided by the Rockefeller Foundation, Monsanto, The Biotechnology Industry Organization, The Council for Biotechnology Information, Grocery Manufacturers of America, and CropLife America.

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30. Field Corn

Insect Resistant (3)

Production

All 48 coterminous states have corn acreage and, in many states, corn is the single most

important crop in terms of acreage and production value. Corn production is centered in

the Midwest, where ten states account for 85% of the US acreage and production.

Individually the states of Illinois and Iowa account for more than 10 million acres of corn

each. Table 30.1 contains estimates of field corn production and acreage for 18 major

corn-producing states for 2000.

Rootworm

Corn rootworms are the most serious insect pests in field corn in the US. There are four

species of corn rootworm found in the U.S.: northern corn rootworm (NCR), western

corn rootworm (WCR), southern corn rootworm (SCR), and Mexican corn rootworm

(MCR). Rootworms causing significant damage in the eastern and western Corn Belt and

some southern states are the NCR and WCR. The SCR occurs in most areas east of the

Rocky Mountains, but is only a potential economic threat in southern states where it

overwinters [2]. The MCR is found in south central states such as Texas, its range having

expanded north from Mexico and Central America [3, 4].

Northern, western and Mexican corn rootworms have similar life cycles, producing one

generation per year [3, 5]. Adult beetles feed on corn pollen, silks, and other plant parts,

as well as pollen from other plants, but adult feeding damage is not normally of economic

importance in corn. Significant rootworm damage is caused by feeding of the larvae on

corn roots.

Adults begin laying eggs in the soil of corn fields in mid to late summer, and the eggs

overwinter in the soil. In late spring or early summer, egg hatch begins and emerging

larvae feed on corn roots for three to four weeks. Larvae then pupate in the soil and

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emerge as adults in the mid summer, beginning the cycle anew. Whereas adults may feed

on plants other than corn, larvae are almost exclusively found in corn, with some minor

occurrence in other grass species.

Southern corn rootworm overwinters as adults in plant litter [2]. Adults become active in

the early spring and lay eggs in the soil in late spring, when corn plants are already in

seedling stage [6]. Eggs hatch after one week and feed on corn roots for two to four

weeks before pupating. A new generation of adults emerges in mid summer. There may

be two or even three generations of SCR per year. Unlike the other corn rootworm

species, the SCR has a wide host range. Larvae can be found in the roots of corn,

peanuts, alfalfa and cucurbits. Adults, also known as spotted cucumber beetles, are

general feeders on almost 300 plant species.

Rootworm Damage

It has been estimated that rootworms cost U.S. corn growers $1 billion annually in

control costs and crop losses. Extension entomologists in 22 states surveyed in 1992

reported that without treatment, yield loss caused by corn rootworm infestations ranged

from 0% to 15%, but could be as high as 50% [1].

Where they occur, WCR, NCR, and MCR are considered primary pests because of their

high potential to damage corn roots. In southern states where these rootworm species do

not occur but where SCR is present, the greater risk posed to corn production by other

insect pests also present generally relegates SCR to being of secondary importance.

Generally, young rootworm larvae tend to feed on root tips, tunneling toward the plant

base, destroying finer roots and root hairs which absorb water and nutrients [5]. Older

larvae tend to feed on the larger roots closer to the plant stalk, consuming more root mass

than the younger larvae.

Damage to roots from rootworm larval feeding reduces the plant’s ability to absorb and

distribute water and nutrients from the soil. Loss of root mass to rootworm feeding

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makes plants susceptible to lodging, which may or may not kill the plant. Lodging that

does not kill the plant increases direct yield losses during harvest by making mechanical

harvesting more difficult, and reduces yield by reducing the amount of light the plant is

able to intercept [7]. Lodging significantly increases the time needed to harvest a field.

In addition to lodging, another way larval rootworm feeding causes indirect losses to corn

is by increasing the incidence of root rots [2, 5]. Rootworm larvae may spread disease

pathogens from infested plants to healthy ones, and feeding wounds created by the larvae

may provide entry points for pathogen infection.

The economic impact of root feeding by corn rootworm larvae can vary with the

circumstances of the infestation, such as how many larvae are present per plant, the age

of the plant when damage occurs, soil fertility and moisture level, and the ability of the

corn variety to regenerate roots [7, 8, 9, 10]. Extrapolating yield losses from root damage

is difficult because of these variations.

Rootworm Control

For three out of the four corn rootworm species damaging U.S. corn, crop rotation has

provided adequate protection in most corn growing areas. Western, northern and

Mexican corn rootworm adults normally lay eggs in corn fields and they do not hatch

until the following season, they have only one generation per year, and their larvae only

feed on corn roots. Consequently, rotating corn with other crops can effectively break the

rootworm life cycle and keep rootworm populations and damage down in the corn

rotation. The most common rotation alternates corn with soybean. Minimizing volunteer

corn plants in non-corn rotations is also important for reducing rootworm populations in

the subsequent corn planting.

Even though crop rotation is the best management strategy for control of WCR, NCR,

and MCR, a large percentage of U.S. corn acreage is not rotated but rather is planted to

continuous corn. There are several possible reasons a grower may plant continuous corn

and risk rootworm damage [1]. Growers who produce corn as feed for their own

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livestock may find it more economical to plant a steady supply of corn rather than

purchase feed offsite during the non-corn rotation years. Corn is more effective at

preventing erosion than is soybean, so growers with sloping land and soil erosion

concerns may find the soil conservation benefits of continuous corn outweigh the risk of

rootworm damage.

Continuous corn plantings are at higher risk of rootworm infestation and damage because

they provide a continuous breeding ground for rootworm. Continuous corn is protected

against rootworm damage by soil applied insecticides. Monitoring root damage and adult

rootworm populations in corn one year can help determine the presence of a larval

rootworm infestation and whether insecticides for larval rootworm control in the

following corn planting will be needed. The percentage of continuous corn acreage in the

eastern and western Corn Belt states treated with insecticides ranges from 7% to 100%

[1].

Crop rotation is not an effective management practice for SCR because of its wide host

range, because egg laying occurs soon after corn fields have been planted and multiple

generations are produced within the same corn field. Other cultural practices are

recommended for SCR management. Plowing or disking at least one month before

planting corn deters further egg-laying in the field. Early planting and high seeding rates,

and other agronomically favorable practices ensure a good stand that may better tolerate

rootworm feeding damage. Soil applied insecticides are the primary tool for protection

against SCR feeding [2], but SCR is not generally the primary target of soil applied

insecticides because in areas where it occurs other soil borne insect pests, pose a greater

and more consistent threat.

Corn Rootworm Insecticides

Efficacy of insecticides applied to the soil for larval rootworm control is affected by a

number of interacting factors [3, 11, 12]. These include properties of the insecticide,

such as toxicity, water solubility and volatility, and the method and timing of application,

as well as parameters of the rootworm larvae population. Coordinating insecticide

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presence and activity in the root zone with rootworm egg hatch is critical. Generally,

insecticides applied at planting will coincide with egg hatch, unless planting is very early

or other factors decrease insecticide activity and availability after it has been applied.

Soil conditions such as type, moisture level and temperature, and presence and

composition of insecticide-degrading microbes in the soil can greatly influence

insecticide activity. Soil that is too warm, too dry or too wet will decrease insecticide

activity and availability.

Historically, insecticides for rootworm control that may be effective upon introduction

within a few years become inconsistent and ineffective in areas of repeated use [3].

Declining efficacy of an insecticide against rootworm larvae, or a reduction in the

consistency of its performance, may result from a number of factors, including changes in

the soil properties which affect insecticide degradation and dissipation, or development of

greater insecticide tolerance in the rootworm which has been associated with broadcast

application of insecticides.

The first soil applied insecticides used against corn rootworm larvae were chlorinated

hydrocarbons such as benzene hexachloride and DDT. They provided efficient rootworm

larvae control for about two decades, until the 1960s [3]. Carbamates such as bufencarb

and carbofuran were introduced for rootworm control in the 1960s and 1970s, but became

inconsistent performers within a decade of introduction. Organophosphates were

introduced for rootworm control around 1980. Currently, larval rootworm control is

dominated by other organophosphates and pyrethroids. Insecticides currently

recommended for rootworm management include chlorethoxyfos, chlorpyrifos,

cyfluthrin, bifenthrin, fipronil, terbufos, tefluthrin, tebupirimphos and phorate.

Beginning in the late 1970’s, insecticide use for corn rootworm management declined as

research showed that rotating out of corn for one year was economically effective and

first year corn did not require insecticide treatment for rootworm [14]. Figure 30.1 shows

soil insecticide use trends in Illinois from 1978 to 1990 [15].

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The estimated use, in 1997, of insecticides for rootworm by state is shown in Tables 30.2

and 30.3. Approximately 12 million pounds of soil-applied insecticides were used in

1997 to control rootworms on 18 million acres in the 18 states.

The high cost of broadcast applications of soil insecticides is prohibitive in field corn, so

banded or furrow applications are made [16]. Insecticides used in banded applications

are applied over a just-planted row in a 7-8 inch band and incorporated by the planter

press wheel and spring-tines or drag chains pulled by the planter [17]. Furrow applied

insecticides are placed in the furrow with seeds at planting. Banded or furrow

applications protect the central root zone but leave the peripheral area between rows

unprotected. Peripheral root pruning may occur in these unprotected zones, but resulting

damage or yield loss is usually not economically significant. In 1992, Extension

Specialists estimated yield losses to corn rootworm with a soil insecticide application to

be 1% to 2% [1]. Large plot insecticide trials performed by Purdue University

researchers from 1991 to 2000 indicate corn rootworm soil insecticides prevented an

average yield loss of 6.5% in comparison to untreated control plots [16].

Insecticides applied to the soil at planting may be either granular or liquid formulations.

For granular applications, the applicator opens the insecticide package and pours the

insecticide into a hopper box, specially designed for pesticide application, which is

mounted on the planter. Material from the hopper box feeds through tubes that deliver it

either with the seed in furrow, or in a band across the row after seed has been planted and

covered but before the press wheel goes over it. The hopper box delivery system must be

carefully calibrated at each use, a time-consuming process that if done incorrectly, may

reduce pesticide efficacy. Liquid applications are often sold in closed box systems that

are mounted on the planter and feed into a system of delivery tubes. The closed box

systems reduce applicator exposure, but most still require equipment calibration.

Whether granular or liquid formulations are used at planting, the application process

complicates the planting process, costing the grower time and money. When planting a

field, stops must be made periodically to refill the planter with seed. If insecticides are

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applied as well, additional stops must be made to refill the hopper box or to replace the

closed liquid insecticide delivery system when material runs out.

Secondary Soil Insect Pests

Soil insecticides applied for corn rootworm larvae control also help control other soil-

borne insect pests in corn, such as wireworms, black cutworms, and white grubs [1].

These pests are considered secondary pests because they are capable of causing economic

damage but do not do so every year or on a large percentage of the acreage [18]. When

and where they do occur, though, they have devastating consequences. Recent trends in

frequency of damage from these secondary pests suggest that they may become an annual

concern for many corn growers.

Wireworms attack seeds or drill into seedling stems below the soil line, weakening or

killing plants. White grubs chew on roots and root hairs, reducing plant vigor or killing

the plant. Wireworms and white grubs are widespread pests with long life cycles of

several years, and high infestations are difficult to predict. Black cutworms feed on

leaves, but economic damage occurs when older larvae feed on stems, cutting the plants

off at or near the soil surface. Black cutworms are widespread but sporadic pests,

causing severe stand reduction where epidemics occur [1].

Timing and location of infestations of these secondary pests are difficult to predict, and

“rescue” treatments applied after infestations are detected are often ineffective [18].

Consequently, insecticides applied to the soil at or near planting are recommended for

corn acreage potentially at risk of attack by these pests.

An alternative to applying soil insecticides is to purchase seed pre-treated with

insecticides. Available seed treatments include one that uses the active ingredient

tefluthrin, and two that use imidacloprid, each at a different rate. The lower rate

imidacloprid seed treatment is marketed for control of secondary soil insect pests, and the

higher rate imidacloprid is marketed for rootworm protection. University studies in Iowa

and Illinois found that seed treatments for rootworm provided inadequate protection

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under moderate to high rootworm pressure, and their use is not recommended at this

point [13, 19].

Seed treatments may provide a viable alternative to soil insecticides for management of

secondary pest damage [18]. In an evaluation of the efficacy of several seed treatments,

on wireworm, tefluthrin and imidacloprid provided control that was statistically similar

and numerically intermediate in terms of damage compared to conventional soil-applied

insecticides (Table 30.4) [29].

Rotation-Resistant Rootworm

Crop rotation has failed to control CRW damage in some areas, resulting in economic

losses in first year corn. New biotypes of western and northern corn rootworm have

appeared that have developed mechanisms of resistance to crop rotation. Table 30.5 lists

the estimated corn acreage at risk of infestation with these new rootworm variants.

Normally in a corn/soybean rotation, WCR and NCR adults lay eggs in corn fields, the

eggs diapause through the winter and when they hatch in spring the field is planted to

soybeans, on which the larvae cannot survive. In addition, adult rootworm beetles will

not lay eggs in fields planted to soybeans, so by the time corn is planted the following

year, the field is free of rootworms. The new biotype of WCR beetles appearing in

eastern Illinois, northern Indiana and parts of Michigan (Figure 30.2), will lay eggs in

soybean fields, so that egg hatch the next season coincides with a corn rotation [20].

WCR in these areas also lay eggs in corn; however, they prefer to lay eggs in late-planted

corn. Although rotation resistant WCR has been assumed to be present in Ohio,

monitoring has failed to confirm the problem [38]. Trapping studies show WCR beetles,

particularly females, fly between cornfields and soybean fields throughout the day [21].

Problems managing NCR with rotation first appeared in the first half of the century, but

frequency, severity, and scope of the problem have increased in the last few decades [22].

In South Dakota, Minnesota, Iowa, and Nebraska (Figure 30.3), NCR have been found

whose eggs exhibit extended diapause [22]. The new NCR biotype diapauses for two

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winters, missing the soybean rotation and hatching out in time to feed on the next corn

rotation.

Reductions in soil insecticide use for rootworm control seen since the 1970s (Figure 30.1)

are at risk of being reversed as growers respond to the new rotation-resistant rootworm

biotypes with increased insecticide use in rotated corn [23]. Indeed, a trend towards

increasing insecticide use in corn in Illinois, where rotation-resistant WCR is the most

widespread, is becoming discernable (Figure 30.4).

Bt Corn for Rootworm

Two new transgenic corn varieties have been developed which produce Bt proteins toxic

to corn rootworm beetles. One variety, developed by Monsanto, produces the Cry3Bb

protein. An application for its registration was submitted to EPA in March, 2001 [24].

The other variety, developed by Dow AgroSciences, Pioneer Hi-Bred, and Mycogen

Seeds, produces a different Bt protein and is currently being field tested under EPA-

granted experimental use permits [25, 26]. The protein produced by Dow AgroScience’s

product has not yet been categorized as a Cry protein but is referred to as the PS-149-B1

protein. Both new transgenic varieties were developed to have resistance to corn

rootworm species.

One potential benefit Bt corn for rootworm protection may offer is more consistent and

reliable protection than that provided by soil insecticides. The efficacy of soil applied

insecticides is dependent on proper timing and placement, and the environmental

conditions that affect insecticide duration in the soil and rootworm larval emergence. If

these factors are not in synchrony, the potential soil insecticides have for high level

rootworm protection is often compromised, making performance inconsistent. The

protection offered by Bt corn for rootworm control is internal and is continually

expressed, maximizing consistency of performance and minimizing risk.

Monsanto’s Bt corn events were evaluated for protection against western and northern

corn rootworm [27, 28]. In terms of level of root damage and consistency of protection,

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these transgenic events performed equally well or better than the soil insecticide

treatments used for comparisons (Tables 30.6 and 30.7).

Estimated Impacts

Corn production areas affected by WCR, NCR, and MCR, such as the eastern and

western Corn Belt, are at risk of consistent economic losses to rootworm feeding and

therefore would be most likely to adopt transgenic corn with rootworm resistance. Areas

affected by SCR (southeastern states) apply few insecticides to specifically target SCR,

and so are unlikely to widely adopt new technology that specifically targets SCR.

It is estimated that acreage likely to be planted to rootworm-protected corn includes corn

acreage that is treated with soil insecticides at planting. In addition, corn acreage that is

at risk of infestation with rotation-resistant rootworm would also be planted to rootworm-

protected corn. Acreage treated in 1997 would include acreage treated for rotation

resistant NCR, which has been a problem for corn growers since the 1980’s. However,

rotation resistant WCR has become increasingly problematic in recent years and is not

reflected in the 1997 insecticide use figures. Therefore, estimated adoption is calculated

as the sum of 1997 acres treated plus acreage infested with rotation resistant WCR (Table

30.8).

Insecticide treatment may still be needed to manage risk of feeding by secondary pests,

especially if their frequency of occurrence continues to increase. This may either be in

the form of current soil insecticides applied at planting, or in the form of an insecticide

treatment coating the Bt seed. If the cost of insecticide-treated Bt seed is still comparable

to the current cost of soil insecticide application, the convenience of having soil insect

protection in and on the seed without having to apply a separate insecticide should

facilitate its adoption.

The insecticide use rate for seed treatment is lower than for soil applied insecticides. The

average application rates by state of insecticides used for rootworm control are shown in

Table 30.3. Average application rates for two seed treatments, calculated assuming a

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seeding rate of 30,000 seeds/acre [33], is 0.013 lb/acre. If rootworm protected Bt corn

seed treated with insecticide for control of secondary pests replaces soil insecticide

applications for rootworm and secondary pest control, insecticide use by state would

decline by between 0.4 and 1.3 lbs/acre.

Assuming that Bt corn for rootworm control provides protection equivalent to that

achieved with soil insecticides, no change in yields is projected. Future research should

indicate whether the increased consistency Bt corn is expected to provide will increase

aggregate yields as well.

The aggregate impact of adoption of Bt corn for rootworm is estimated to be a 14 million

lbs reduction in insecticides (Table 30.9).

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Table 30.1 Corn for Grain: 2000 State Harvested

(000A) Yield

(BU/A) Production

(Million Bushels) Price Per Bushel

($) Value of Production

(Million $) CO 1180 127 149 2.15 322 IL 11050 151 1668 1.90 3170 IN 5550 147 815 1.85 1509 IA 12000 145 1740 1.75 3045 KS 3200 130 416 2.05 852 MD 405 155 62 2.00 125 MI 1970 124 244 1.90 464 MN 6600 145 957 1.75 1674 MO 2770 143 396 1.70 673 NE 8050 126 1014 1.95 1977 NY 480 98 47 2.20 103 ND 930 112 104 1.60 166 OH 3300 147 485 2.00 970 OK 270 140 37 1.90 71 PA 1080 127 137 2.00 274 SD 3850 112 431 1.60 689 TX 1900 124 235 2.15 506 WI 2750 132 363 1.90 689 Total 67335 138 9300 1.86 17279 US Total 72732 137 9968 1.87 18621

Sources: [31, 39]

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Table 30.2 Corn Rootworm Insecticide Use in 1997 by State and Active Ingredient

State Active Ingredient

Percent of Acres Treated

Application Rate (lbs AI/acre)

Acres Treated

Total Pesticide Use (lbs)

Colorado CHLORETHOXYFOS 1 0.5 10,161 5,081 CHLORPYRIFOS 1 0.76 8,637 6,564 PHORATE 1 1.2 10,161 12,194 TEFLUTHRIN 1 0.08 10,161 813 TERBUFOS 17 1.26 172,742 217,655Colorado Total 211,863 242,306Illinois CHLORETHOXYFOS 2 0.16 216,584 34,653 CHLORPYRIFOS 8 1.1 736,385 810,023 CYFLUTHRIN + TEBUPIRIMPHOS 2 0.005 216,584 20,575 PHORATE 1 1.11 108,292 120,204 TEFLUTHRIN 7 0.09 758,043 68,224 TERBUFOS 5 0.86 541,459 465,655Illinois Total 2,577,347 1,519,335Indiana CHLORETHOXYFOS 6 0.16 334,575 53,532 CHLORPYRIFOS 6 1.05 284,389 298,609 CYFLUTHRIN + TEBUPIRIMPHOS 8 0.006 446,100 60,670 PHORATE 1 1.11 55,763 61,896 TEFLUTHRIN 8 0.08 446,100 35,688 TERBUFOS 8 1.25 446,100 557,626Indiana Total 2,013,028 1,068,020Iowa CHLORETHOXYFOS 2 0.16 236,737 37,878 CHLORPYRIFOS 6 1.73 603,680 1,044,366 CYFLUTHRIN + TEBUPIRIMPHOS 3 0.01 355,106 49,715 PHORATE 1 0.96 118,369 113,634 TEFLUTHRIN 5 0.12 591,843 71,021 TERBUFOS 3 1.03 355,106 365,759Iowa Total 2,260,840 1,682,372Kansas CHLORPYRIFOS 6 0.68 133,364 90,688 TEBUPIRIMPHOS 3 0.13 78,450 10,198 TEFLUTHRIN 6 0.12 156,899 18,828 TERBUFOS 8 1.08 209,199 225,935Kansas Total 577,912 345,649Maryland

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CHLORPYRIFOS 11 0.97 46,616 45,218 TEFLUTHRIN 10 0.1 49,857 4,986 TERBUFOS 2 1.07 9,971 10,669Maryland Total 106,444 60,873Michigan CHLORETHOXYFOS 2 0.16 48,041 7,687 CHLORPYRIFOS 6 1.1 122,506 134,756 PHORATE 2 0.97 48,041 46,600 TEFLUTHRIN 8 0.08 192,166 15,373 TERBUFOS 7 0.92 168,145 154,693Michigan Total 578,899 359,109Minnesota CHLORPYRIFOS 4 1.17 226,638 265,166 PHORATE 2 0.97 133,316 129,317 TEFLUTHRIN 4 0.08 266,633 21,331 TERBUFOS 3 1.03 199,974 205,974Minnesota Total 826,561 621,787Missouri CHLORETHOXYFOS 2 0.16 51,069 8,171 CHLORPYRIFOS 7 1.53 151,929 232,452 PHORATE 1 0.96 25,534 24,513 TEBUPIRIMPHOS 2 0.09 51,069 4,596 TEFLUTHRIN 1 0.05 25,534 1,277 TERBUFOS 1 0.9 25,534 22,981Missouri Total 330,669 293,989Nebraska CHLORETHOXYFOS 1 0.5 84,891 42,445 CHLORPYRIFOS 6 0.68 432,943 294,402 CYFLUTHRIN + TEBUPIRIMPHOS 12 0.006 1,018,690 128,355 PHORATE 2 0.79 169,782 134,128 TEFLUTHRIN 8 0.1 679,127 67,913 TERBUFOS 9 1.15 764,018 878,620Nebraska Total 3,149,451 1,545,863New York CHLORPYRIFOS 15 1.5 144,085 216,128 TEFLUTHRIN 65 0.2 734,552 146,910 TERBUFOS 2 1.07 22,602 24,184New York Total 901,239 387,222North Dakota PHORATE 5 1.3 37,161 48,310 TEFLUTHRIN 1 0.12 7,432 892 TERBUFOS 11 1.31 81,755 107,099North Dakota Total 126,349 156,301Ohio

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CHLORETHOXYFOS 6 0.16 213,315 34,130 CHLORPYRIFOS 10 1.2 302,196 362,636 PHORATE 1 1 35,553 35,553 TEFLUTHRIN 10 0.13 355,525 46,218Ohio Total 906,589 478,537Oklahoma CHLORPYRIFOS 1 1.0 1477 1477 TEFLUTHRIN 8 0.12 13901 1668 TERBUFOS 8 1.0 13901 13901Oklahoma Total 29279 17046Pennsylvania CHLORPYRIFOS 11 0.97 136,122 132,038 CYFLUTHRIN + TEBUPIRIMPHOS 7 0.005 101,909 11,720 PHORATE 1 1 14,558 14,558 TEFLUTHRIN 10 0.1 145,585 14,558 TERBUFOS 2 1.07 29,117 31,155Pennsylvania Total 427,291 204,030South Dakota CHLORETHOXYFOS 1 0.5 34,832 17,416 CHLORPYRIFOS 9 1.8 266,467 479,641 PHORATE 5 1.3 174,161 226,410 TEFLUTHRIN 2 0.14 69,665 9,753 TERBUFOS 11 1.31 383,155 501,933South Dakota Total 928,281 1,235,153Texas CHLORPYRIFOS 4 0.84 59,780 50,215 TERBUFOS 28 1.04 492,306 511,998Texas Total 552,085 562,213Wisconsin CHLORETHOXYFOS 2 0.16 71,910 11,506 CHLORPYRIFOS 9 1.04 275,057 286,060 PHORATE 2 0.97 71,910 69,753 TEFLUTHRIN 10 0.09 359,552 32,360 TERBUFOS 10 1.07 359,552 384,721Wisconsin Total 1,137,982 784,399 Source: Calculated from [30]. Assumes 85% of chlorpyrifos use is targeted at rootworms.

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Table 30.3. State Summary of Corn Rootworm Insecticide Use in 1997

State

Acres Treated (000)

Total Pesticide

Use (000lbs)

Application Rate

(lbs/acre) Colorado 212 242 1.14Illinois 2,577 1,519 0.59Indiana 2,013 1,068 0.53Iowa 2,261 1,682 0.74Kansas 578 345 0.60Maryland 106 60 0.57Michigan 579 359 0.62Minnesota 827 621 0.75Missouri 331 293 0.89Nebraska 3,149 1,545 0.49New York 901 387 0.43North Dakota 126 156 1.24Ohio 907 478 0.53Oklahoma 29 17 0.48Pennsylvania 427 204 0.48South Dakota 928 1,235 1.33Texas 552 562 1.02Wisconsin 1,138 784 0.69Total 17641 11557 0.66

Source: See Table 30.2

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Table 30.4. Wireworm Insecticide Evaluation

Active Ingredient Insecticide Rate Placement

% Damage

Terbufos Counter 20CR 1.2 Furrow 9 a Terbufos Counter 20CR 1.2 T-band 12 a Terbufos Counter 20CR 0.6 Furrow 13 a Chlorethoxyfos Fortress 5G 0.15 Furrow 14 a Tefluthrin Force 3G 0.15 Furrow 17 a Tebupirimphos Aztec 2.1G 0.07 Furrow 25 ab Tefluthrin ProShield ST 0.075 Seed Trt 27 ab Tefluthrin Force 3G 0.15 T-band 27 ab Tebupirimphos Aztec 2.1G 0.14 Furrow 28 ab Imidacloprid Gaucho ST 0.16 mg/seed Seed Trt 29 ab Imidacloprid Adage ST 50 g/100 kg seed Seed Trt 31 ab Fipronil Regent 4SC 0.12 Furrow 39 ab Fipronil Regent 4SC 0.09 Furrow 44 ab Check 72 b

Notes: Results followed by same letter are not statistically different. Treatment rates as oz. a.i./1000 row feet. Source: [29]

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Table 30.5. Estimated Corn Acreage at Risk of Infestation with Rotation-Resistant Corn Rootworm.

Western Corn Rootworm Northern Corn Rootworm

State Acreage State Acreage

Illinois 3,259,520 Iowa 3,287,200

Indiana 2,830,880 Minnesota 2,279,280

Michigan 309,600 South Dakota 1,504,000

Nebraska 572,800

Total 6,400,000 Total 7,643,280

Note: Calculated assuming 80% of corn acreage in counties at risk for rotation resistant CRW populations are rotated corn. Source: [11,22, 35, 36, 37]

Table 30.6. Root Ratings for Bt Corn Events Versus Conventional Insecticides

Treatment Root Rating

Counter 20CR (Terbufos) 1.6 d

Force 3G (Tefluthrin) 1.6 d

Lorsban 15G (Chlorpyrifos) 2.0 cd

Event A 2.2 c

Event B 2.6 b

Event C 2.2 c

Event D 1.0 e

Untreated 4.2 a

Root ratings on a 1-6 scale, with 1 = no observable rootworm feeding scars present and 6 = three or more full nodes of roots pruned [32]. Means followed by the same letter within a column are not significantly different Source: [27]

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Table 30.7. Rootworm Control Efficacy of Bt Corn Events Versus Conventional Insecticides Node-injury

Treatment Full Partial (%) % Consistency a

Counter 20CR (Terbufos) 0 37 ab 45 bc

Event A 0 7 a 95 a

Event B 0 2 a 100 a

Event C 0 2 a 100 a

Event D 0 1 a 100 a

Force 3G (Tefluthrin) 0 22 ab 75 ab

Lorsban 15G (Chlorpyrifos) 0 64 b 20 c

Untreated check 0 65 b 25 c

Means followed by the same letter within a column are not significantly different. Node-injury scale: 0.01-no feeding damage; 1-one node, or the equivalent of an entire node, eaten back to within approximately 2 inches of the stalk., etc. Damage in between complete nodes destroyed is noted as the percentage of the node missing. a Percent consistency equals the percentage of times a treatment limited feeding damage to ¼ node or less. Source: [28]

21

Table 30.8 Estimated Adoption of Bt Corn for Rootworm by State

State

Acreage Treated in1

1997 (000A)

Rotation Resistant

WCR Acreage2 (000A)

Total Adoption (000A)

CO 212 0 212IA 2,261 0 2,261IL 2,577 2,934 5,511IN 2,013 2,548 4,561KS 578 0 578MD 106 0 106MI 579 279 858 MN 827 0 827MO 331 0 331ND 126 0 126NE 3,149 0 3,149NY 901 0 901OH 907 0 907OK 29 0 29PA 427 0 427SD 928 0 928TX 552 0 552WI 1,138 0 1,138 17,641 5,761 23,402 1See Table 30.3 2Rotation-resistant acreage with economic levels of rotation resistant WCR calculated assuming 90% of rotation resistant acreage is treated (see Table 30.5).

22

Table 30.9 Estimated Impacts of Bt Corn for Rootworm by State

Adoption Acreage1 Pesticide Use Reduction2

(lbs AI/yr.)

CO 212000 239000 IA 2261000 1643000 IL 5511000 3179000 IN 4561000 2358000 KS 578000 339000 MD 106000 59000 MI 858000 517000 MN 827000 609000 MO 331000 290000 ND 126000 154000 NE 3149000 1502000 NY 901000 375000 OH 907000 469000 OK 29000 17000 PA 427000 199000 SD 928000 1222000 TX 552000 555000 WI 1138000 770000 TOTAL 23,402,000 14,496,000

1 See Table 30.8

2 Calculated with average use rates shown in Table 30.3 minus .013 lb/A to account for seed treatment use.

23

Figure 30.1. Trends in soil insecticide use on corn in Illinois (1978 – 1990)

Source: [15]

0

20

40

60

80

100

1978 1982 1985 1988 1990

% crop treated

24

Figure 30.2. Areas with Rotation Resistant Western Corn Rootworm

Sources: [11,22,35,37]

25

Figure 30.3. Areas with Rotation Resistant Northern Corn Rootworm

Source: [22]

26

Figure 30.4. Insecticide Use in Illinois Corn (1991 – 2001)

05

101520253035404550

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

Source: [34]

% Acres Treated

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Soybeans, USDA NAPIAP Report Number 1-CA-95, 1995.

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AG-271, 1982. Available on the internet at

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28

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29

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30

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