Insecticides Used by Minnesota Processors
to Control European Corn Borer
and Corn Earworm in Sweet Corn

G. J. Gingera, Bh. Subramanyam and W. D. Hutchison

Copyright ©  2009  Regents of the University of Minnesota. All rights reserved.

Introduction

In the United States, Minnesota ranks second in sweet corn production. Most of the sweet corn in Minnesota is produced for processing.

The economically important moth pests of sweet corn in Minnesota are the European corn borer (ECB), Ostrinia nubilalis, and the corn earworm (CEW), Helicoverpa zea. ECB larvae damage sweet corn by tunneling all parts of the plant, including the ear, stalk, and tassel. Each year, ECB usually completes two generations in southern Minnesota and one generation in northern Minnesota. Because of continuous planting from April to July, ECB damage may occur on both early and late planted sweet corn. The pest overwinters in old stalks and cobs as fully grown (late-instar) larvae. Moths emerge in late spring or early summer, and infest the tallest or most mature corn fields. Mated females lay egg masses on the underside of leaves. Larvae hatch from egg masses within five to seven days and begin tunneling into the stalk or ear during the second or third instar (five to eight days after hatch). Although whorl-stage ECB infestations may cause yield reductions in some hybrids, the primary concern among processors is the risk of larval infestation and contamination of the ears.

Every year, adult CEW migrate from the southern states and infest Minnesota sweet corn. The first moths typically arrive in mid-June to early July; the primary flight, however, occurs in late August. Eggs are laid singly on corn silks. Larvae hatch from eggs and immediately travel down the silk channel to the ear tip, where they are well protected from insecticides. Therefore, control of CEW is challenging.

As part of the Minnesota Pesticide Impact Assessment Program for vegetable crops, a survey was conducted in 1990 to obtain more representative estimates of insecticide use on sweet corn. Here, we provide a summary of insecticides used to control ECB and CEW in sweet corn grown for processing.

Survey Procedures

A single page survey questionnaire was distributed to sweet corn processors during 1990, as a part of the Minnesota Vegetable Processors' Newsletter, Volume 5, No. 4. The survey consisted of 14 questions, dealing primarily with ECB and CEW infestation problems on sweet corn. Most of the questions required filling in blank spaces, ranking insecticides used, and providing information on types of insecticides used and number of applications made.

Data Analysis

A total of 13 processors returned the survey form. Of the 13 processors, seven produced sweet corn in states neighboring Minnesota. In this report, we summarize data from six sweet corn processors in Minnesota. The total sweet corn acres and number of fields for each processor were tabulated. The percentage of processors viewing either ECB or CEW as the primary pest, and the number of processors using different insecticides against first and second generations of ECB or against second generations of both ECB and CEW, were computed. For each reported insecticide, the amount of active ingredient used to control ECB or CEW was calculated as follows:

(Number of acres) x (fraction of acres treated) x (rate) x (number of applications)

Rate was expressed as pounds of active ingredient (AI) per acre. Pounce (permethrin) and Asana (esfenvalerate) were the only two insecticides used for ECB and CEW control. For Pounce, a rate of 0.15 pounds AI per acre was used per application; for Asana, a rate of 0.05 pounds AI per acre was used per application. Unless otherwise indicated by the processors, we assumed that 100 percent of the crop acres were treated with these insecticides.

Results

In 1990, sweet corn for processing was harvested from 130,000 acres with an estimated market value of $47 million, according to the Minnesota Agricultural Statistics Service. Sweet corn acreage and the number of fields among the six processors ranged from 8,800–49,500 and 150–990, respectively (Table 1). Total reported acreage of the six processors was 100,400, which represented 77% of the total 1990 Minnesota sweet corn acreage. Most of the reported acreage was in south central Minnesota.

During 1990, three of the six processors perceived CEW to be slightly more of a pest problem than ECB, while two processors overwhelmingly perceived ECB to be a serious pest relative to CEW (Table 2). One processor felt both insect pests were equally severe.

The Minnesota Extension Service in 1990 recommended the following insecticides for ECB control in sweet corn: carbofuran, chlorpyrifos, diazinon, methomyl, methyl parathion, permethrin, and Bacillus thuringiensis var. kurstaki. Recommended insecticides for CEW control were: carbaryl, diazinon, esfenvalerate, ethyl parathion, methomyl, methyl parathion, parathion, and permethrin. The Minnesota Extension Service also recommended pest action thresholds for making pesticide treatment decisions. Except for the removal of diazinon, and the addition of carbaryl, the insecticides listed above are currently recommended by the Minnesota Extension Service for ECB control. Recommendations for CEW control have essentially remained the same except for the deletion of ethyl parathion.

Insecticides preferred by processors for control of ECB and CEW are shown in Table 3. Pounce was the most commonly used insecticide to control first and second generations of ECB, and second generations of both ECB and CEW. Besides Pounce, Asana was used by one processor for ECB and CEW control. For ECB and CEW control, Ambush (permethrin), Lannate (methomyl), and Penncap-M (methyl parathion) were preferred to a lesser extent. However, these insecticides were not used during 1990.

Three of the six processors applied Pounce one to two times to control first generation ECB (Table 4). All six processors made one to three applications of Pounce to control second generation ECB. For controlling second generations of both ECB and CEW, one to three applications of Pounce or Asana were made by all six processors. These applications resulted in the use of a total of 6,290 pounds AI of Pounce to control first generation ECB, and 35,610 pounds AI of Pounce to control second generation ECB (Table 5). For controlling second generations of both ECB and CEW, a total of 21,540 pounds AI of Pounce and 1,440 pounds AI of Asana were used on the reported 100,400 acres.

In summary, on 77% of the total Minnesota sweet corn acreage, about 63,440 pounds AI of Pounce and 1,440 pounds AI of Asana were used during 1990.

Gloria J. Gingera former research specialist Department of Entomology University of Minnesota

Bh. Subramanyam assistant extension entomologist and coordinator of the Minnesota Pesticide Impact Assessment Program Department of Entomology University of Minnesota

W. D. Hutchison extension entomologist Department of Entomology University of Minnesota

Produced by Communication and Educational Technology Services, University of Minnesota Extension.

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