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  • Components of Management | The European Corn Borer
    Agents Transgenic Corn Weather Cultural Practices Commodities Sweet Corn Popcorn Seed Corn Peppers Snap Bean Cotton Wheat Potato Other Crops Predictive Models Galleries Good decisions for managing European corn borer depend on several biological and economic factors Researchers from several states cooperating and coordinating their investigations through the NC 205 Regional Research Project on Integrated Crop Management Effects on Stalk boring Lepidoptera are accumulating data to update the European corn borer management models they have developed Over a 5 year period the component of the management model that predicts the time of egg laying for the second generation has been tested in numerous fields in seven states In all but one field the model s predictions were within 3 days of the actual second generation egg laying period Simple management models for European corn borer are presented in the following sections with appropriate examples and calculation charts for reaching a management decision More complex yet easy to use microcomputer management models are available from the Cooperative Extension Services at Iowa State Kansas State Pennsylvania State and Nebraska Universities In regions where intensive management of corn production occurs European corn borer is usually not the only pest Pest management specialists operating

    Original URL path: http://www.ent.iastate.edu/pest/cornborer/manage (2015-11-11)
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  • Scouting Techniques | The European Corn Borer
    Timing Insecticide Treatment Application Equipment Resistant Varieties Biological Agents Transgenic Corn Weather Cultural Practices Commodities Sweet Corn Popcorn Seed Corn Peppers Snap Bean Cotton Wheat Potato Other Crops Predictive Models Galleries Management The value of a pest management scouting program comes from the site specific information that assists with decision making Without this information a farmer often must rely on guesswork to apply a control Scouting is used to sample

    Original URL path: http://www.ent.iastate.edu/pest/cornborer/manage/scout (2015-11-11)
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  • First Generation | The European Corn Borer
    assessment depends on using good sampling technique to get a close representative of the true population Where possible samples should be taken from five representative sets of 20 plants for every 40 to 50 acres Although less precise a practical compromise for very large fields 80 acres or more is limiting surveys to five sets of 25 consecutive plants per field Chances of making a poor decision increase greatly if fewer samples are taken Chemical control can be expensive and harmful to beneficial organisms such as insect predators parasites and pollinators If there is any doubt about the level of infestation more samples should be collected European corn borer moths and egg laying may be concentrated along field edges grass waterways or access roads Sampling European corn borer infestations along these edges does not give an accurate estimate of the field population To eliminate the influence of border areas the first sample should be taken after walking 100 feet or more into the field Samples should represent all topographical environmental and cultural features that may create changes in plant height plant maturity and plant density Sampling only plants that show larval injury should be avoided Sampling only infested plants could inflate the population estimate If more than one variety is planted in the same field consider each variety as a separate field for scouting purposes Figure 21 Grabbing and pulling the whorl by hand to detach it from the plant for examination M E Rice Figure 22 Unwrapping and carefully examining whorl leaves for fresh feeding injury and live larvae M E Rice Treatment guidelines for corn attacked in the whorl stage are based on active whorl feeding which is indicated by fresh leaf damage Figure 15 and live larvae inside the whorl Whorl feeding can be assessed by grabbing

    Original URL path: http://www.ent.iastate.edu/pest/cornborer/manage/first (2015-11-11)
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  • Second Generation | The European Corn Borer
    of second generation European corn borer and this is largely influenced by crop growth stage Fields that are shedding pollen and have green silks present are more attractive and frequently have more problems than fields approaching brown silk stage corn After the brown silk stage has started there is no need to scout for new egg masses if the economic threshold has not been reached by this time because this stage of corn is no longer attractive to egg laying females In corn that has tasseled scout the field for egg masses by examining the underside of corn leaves Mark off 20 plants in a row Count the number of egg masses on the middle seven leaves of each plant the ear leaf and the three leaves above and the three leaves below Repeat this procedure at four more representative field locations This will give a total of 100 plants that have been scouted for egg masses Divide the number of egg masses counted by 91 The resulting number will estimate the egg masses per plant as if all of the leaves had been examined For instance if 27 egg masses had been found on the middle seven leaves of 100 plants 0 27 egg mass per plant dividing this number by 91 gives an estimate of 0 30 egg mass per plant Use this value for the number of egg masses per plant in Table 3 to estimate the population density of larvae per corn plant Research has indicated that this is an accurate time saving procedure that eliminates the need to look on the underside of each leaf Table 3 Predicted potential population densities of European corn borer larvae for various egg mass densities per whole corn plant or corrected egg mass densities if 7 leaf count useda collected on different dates during the oviposition egg laying period Predicted number of larvae per plant at designated days after initiation of egg laying and proportion of egg laying complete in parentheses Number of egg 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 masses plant 125 180 245 320 405 500 595 680 755 820 875 920 955 980 995 1 00 0 02 0 72 0 50 0 37 0 28 0 22 0 18 0 15 0 13 0 12 0 11 0 10 0 10 0 09 0 09 0 09 0 09 0 04 1 44 1 00 0 74 0 56 0 44 0 36 0 30 0 26 0 24 0 22 0 21 0 20 0 19 0 18 0 18 0 18 0 06 2 24 1 56 1 14 0 88 0 69 0 56 0 47 0 41 0 37 0 34 0 32 0 30 0 29 0 29 0 28 0 28 0 08 2 96 2 06 1 51 1 16 0 91 0 74 0 62 0 54 0 49 0 45 0 42 0 40 0 39

    Original URL path: http://www.ent.iastate.edu/pest/cornborer/manage/second (2015-11-11)
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  • Reaching a Management Decision With Economic Injury Levels and Economic Thresholds | The European Corn Borer
    2 50 per bushel insecticide and application costs of 14 00 per acre and 67 percent control with the insecticide The break even point is 1 19 larvae per plant An infestation higher than this would cause an economic loss The economic threshold ET is a slightly smaller number and represents the insect density at which control measures should be initiated to prevent the pests from exceeding the economic injury level However there is variation among these values depending on many factors such as variety fertility moisture and season At best these numbers represent best estimates and should be regarded as being within the ball park One of the greatest values of the economic threshold concept is monitoring the buildup of potentially damaging pest populations and reaching a control or management decision before economic yield losses occur A cost benefit analysis which incorporates economic thresholds can be used to help make management decisions In conducting this analysis it is helpful to use a prepared form to follow the proper sequence of calculations An example of a calculation form is given in Table 5 and a blank form for copying is available for first generation in whorl stage corn All percentages on this form must be calculated by using decimals i e 80 percent 0 8 The number of larvae per plant is determined by appropriate sampling of eggs or live larvae as discussed previously The analysis is straightforward but there are several limitations to its use First is the number of European corn borers per plant that can be figured into the equation The survivorship of first and second instars usually ranges from 20 to 50 percent depending on the stage of development at the time scouting takes place and the extremes of environmental stress before larvae bore into the

    Original URL path: http://www.ent.iastate.edu/pest/cornborer/manage/decision (2015-11-11)
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  • First Generation in Whorl-Stage Corn | The European Corn Borer
    in 100 corn plants About two thirds of the larvae are in the second instar and the environmental conditions are considered to be moderate Consequently survivorship is estimated to be 0 40 40 percent Therefore 180 larvae out of the 450 found are expected to bore into 100 plants later in development Larvae per plant is calculated at 1 8 Since the yield loss for field corn in the 10th leaf stage of development is expected to be 5 9 percent per larva the proportion of yield loss per larva is 0 059 The proportion of yield loss from the European corn borer larval population found in the field is 0 106 which is the yield loss calculation This means that 10 6 percent of the yield could be lost to European corn borer if the field goes untreated The producer has averaged 140 bushels per acre over the past 10 years and wants to use this average for analysis on the field The predicted bushels lost per acre is 14 84 based on the proportion of yield loss and expected yield At 2 50 per bushel the value of corn that would be lost per acre is 37 10 If treatment is required the producer predicts that the proportion of larvae controlled by applying a spray in the whorl would be 0 8 80 percent Multiplying this number by the loss per acre equals 29 68 preventable loss that can be saved by applying a control Subtracting the cost of control from the preventable loss will give the amount of money either gained or lost if the control is applied Cost of control includes both the application cost andinsecticide cost for one application In this example if the cost of control is 14 00 there is a net gain

    Original URL path: http://www.ent.iastate.edu/pest/cornborer/manage/whorl (2015-11-11)
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  • Second Generation in Tassel-Stage or Later Corn | The European Corn Borer
    predict the potential European corn borer population density and the necessity for an appropriate management decision To calculate percentage of eggs laid the shape and length of the egg laying period must be estimated as described in the scouting section Assuming that the average number of eggs per mass and the length and shape of the egg laying period are reasonable the percentage of eggs laid for any sample date in that period can be calculated Table 3 compiles predicted population densities of larvae using these assumptions First determine how many days the European corn borers are into the egg laying period Second find the day from 5 to 20 at the top of Table 3 that corresponds with the number of days after the start of egg laying and the proportion of egg laying completed Third in the left hand column find the number that best matches the adjusted number of egg masses found per plant when scouting the field Fourth scan across the chart moving to the right until intersecting the column that matches the day of the egg laying period when the field was scouted This is the row of numbers that runs from 5 to 20 The percentages written as decimal proportions of egg laying that have been completed by that particular date are located immediately below the row of numbers that runs from 5 to 20 Fifth the number where the column and row intersect is the predicted number of larvae per plant This number is entered in the last blank on line 4 of the second generation cost benefit analysis chart Table 6 Cost benefit analysis example of European corn borer management in tassel stage or later corn view blank form 1 8th day of scouting 0 day egg laying started 8 days after first eggs laid 2 24 egg masses found 0 91 for middle 7 leaf samples 26 adjusted egg masses 3 26 adjusted egg masses 100 plants examined 0 26 egg masses per plant 4 8 days after first eggs laid 0 26 egg masses per plant 3 75 larvae per planta 5 3 75 larvae per plant X 0 04 yield loss per larvab c 0 15 yield loss 6 0 15 yield loss X 140 expected yield bushels per acre 21 bushels loss per acre 7 21 bushels loss per acre X 2 50 price per bushel 52 50 loss per acre 8 52 50 loss per acre X 0 67 percent controlb 35 18 preventable loss acre 9 35 18 preventable loss acre 14 00 cost of control per acre 21 18 profit loss per acre a Take from Table 3 b All percents must be written using decimals i e 50 percent 0 5 c Use 0 04 for pollen shedding corn 0 031 for blister stage corn or 0 024 or dough stage corn In the Table 6 example egg laying began 8 days beforehand and field scouting reported 24 egg masses on the middle seven

    Original URL path: http://www.ent.iastate.edu/pest/cornborer/manage/tassel (2015-11-11)
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  • Cost-Benefit and Economic Injury Level Computations | The European Corn Borer
    If more specific local information is not available the suggested value is 23 EM The average number of egg masses per plant based on the latest scouting reports Count both hatched and unhatched egg masses PO The proportion of the total egg complement deposited oviposited by the time the sample egg mass collection EM was taken The formulas for estimating PO are given below and can be programmed easily on a microcomputer Case 1 If the sample date is later than or equal to the termination of egg laying then PO 1 0 Case 2 If the egg mass sample date for density estimation is earlier than or equal to the peak in egg laying and occurs after initiation of egg laying then PO x 2 a a b Case 3 If the egg mass sample date for density estimation is later than the peak of egg laying but before the termination of egg laying then PO 1 a b x 2 b a b where x Sample date ÃƒÆ initiation of egg laying date a Days from initiation of egg laying to peak of oviposition b Days from peak to termination of egg laying The same variables used to calculate the cost benefit analysis can be used to calculate the EIL for any set of economic and biological conditions The EIL is calculated using the following equation CC PL x MV x EY x PC All variables are defined and used the same as for the cost benefit analysis presented earlier The break even point occurs when the PPD is equal to the EIL For example assume a field of corn is shedding pollen when the majority of egg hatch is expected The anticipated yield without European corn borer damage is 150 bushels per acre The corn has an anticipated market value of 2 50 per bushel and the total control cost for one application is 14 00 per acre The application is expected to kill 67 percent of the larvae PC 0 67 Thus EIL 14 00 0 04 x 2 50 x 150 x 0 67 EIL 14 00 per acre 10 05 per acre EIL 1 39 larvae per plant will cause damage by the seasonÃƒÆ Ã â  s end This is also the break even point Because all the variables for EIL are known or can be estimated beforehand and because a decision for a control action is best made when eggs are present it is more useful to express the EIL as egg masses per plant that will result in an economic larval density By converting to egg masses per plant samples of egg masses can be taken to determine if the EIL for egg masses is exceeded Then the user would have time to take action before larvae bore into the plant and gain protection against contact insecticides Under these assumptions the number of egg masses per plant resulting in the EIL is also the economic threshold ET Using the information from

    Original URL path: http://www.ent.iastate.edu/pest/cornborer/manage/costbenefit (2015-11-11)
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