ISU Extension Integrated Crop Management Newsletter
June 18, 1993

Announcement

Certified Crop Advisor test

The Iowa Certified Crop Advisor (CCA) State Board will offer the National and State CCA exam in Ames on August 6. Only one testing location is being offered because the board expects low attendance due to the late crop season. The next testing date is February 4, 1994.

Applications for taking the exam can be requested from the Iowa Fertilizer and Chemical Association by calling Jodie at 800-383-1682. Form I of the application must be returned to the American Society of Agronomy by July 9, 1993. The fee for both the State and National Exam is $115.

The Iowa portion of the CCA exam is being developed and will be pre-tested before the end of June. Because the National Exam must be general, the Iowa exam will emphasize crop production and pest management, including insect and weed identification. Training programs and materials are available from a variety of sources including ISU Extension, Wilbur-Ellis, Agricom, Cenex Land O'Lakes, Farmland, Agri-Growth, and Terra International. This list may not be complete. Training providers should contact the IFCA with details of opportunities available.

ISU Extension Integrated Crop Management Newsletter
June 18, 1993

Corn borer software available
by Marlin E. Rice, extension entomologist

What is the economic threshold for first-generation corn borers, or second-generation corn borers? When should fields be scouted during the second generation? These are questions that have no firm, standard answers but that many farmers and crop advisors ask each year. A computer program useful in answering these questions is available for Iowa corn. The three-part software focuses on first- and second-generation management, and prediction of second-generation egg laying.

First-generation management

To effectively and economically manage first generation corn borers, fields must be scouted, the treatment economics must be analyzed, and, if it is needed, an insecticide must be applied before larvae begin boring into the plant. The software calculates the expected dollar loss, based on the number of larvae per plant, the plant stage (the smaller the plants, the greater the yield loss), and the expected value of the crop per acre. These values are used to determine whether the benefits of an insecticide exceed the value of crop loss and application costs. A recommendation is then given regarding whether a treatment is economically profitable.

Predicting second-generation egg laying

First-generation larvae can be collected, and their age determined based upon their size. This information then is entered into the computer program. Daily high and low temperatures are used to predict when the larvae will become moths and lay eggs. The predictions help pinpoint when scouting should be done. Scouting is suggested between the 25 and 50 percent egg-laying dates.

Second-generation management

This is similar to the first generation management and evaluates the costs of an insecticide versus the benefits based upon the corn borer population in the field and the crop market value.

The benefits of this program are twofold. First, the management costs are easy to calculate and can help you determine whether an insecticide application will provide a potential economic return for either first- or second-generation corn borers. Second, the software predicts when fields should be scouted for second-generation problems. Second-generation corn borers no longer need to be ignored because they can be more effectively scouted, and the control costs and benefits can be determined.

The European corn borer phenology and management software is available for $75 from ISU Extension Software Service, 108 Atanasoff Hall, Iowa State University, Ames, Iowa 50011 or by calling 515-294-8658. Please indicate 5 1_4" or 3 1_2" disk size when ordering. It is for MS DOS and compatible microcomputers and requires two floppy disk drives or a hard disk. A minimum of 512K RAM, DOS 3.0 or higher is required.

ISU Extension Integrated Crop Management Newsletter
June 18, 1993

How late can one plant soybeans?
by Garren O. Benson, extension agronomist

It is likely that some Iowa farmers may be planting some soybeans into early or mid-July. What are the yield prospects for these very late plantings?

The research base is limited as few tests include planting dates such as July 1, July 10, or July 20. During the mid-1970's the author had five years of tests at three Iowa locations that included these as well as earlier dates. The sites were at Sutherland and Kanawha in northern Iowa and Beaconsfield in southern Iowa. Based on normal planting dates, varieties classified as adapted, early and very early in maturity were used.

For July 1 plantings, the northern Iowa sites averaged in the 20 to 25 bu/A range. At the southern Iowa site 25 to 30 bu/A was typical. As one would expect, the year to year range in yields for these very late plantings varied greatly. Even when the most appropriate variety maturity was selected, the yield range at the northern sites were from the mid-teens to 40 bu/A.

For the northern locations, beans planted July 10 averaged from 12 to 16 bu/A with a yearly range from zero to nearly 30 bushels. Average yields at the southern Iowa site were 22 bu/A for July 10 planting. Results from July 20 plantings were extremely variable. Dry surface soils that slow germination were a problem some years.

When deciding how late to plant, sufficient yield to at least cover variable costs (seed, seedbed preparation, etc.) would certainly be a major consideration. However, providing ground cover, preventing "fallow syndrome" in 1994 corn, and meeting various program requirements, also may be considerations. Typical cut-off dates based on yield expectations are July 5 to 10, July 10 to 15, and July 15 to 20 for northern, central, and southern Iowa respectively.

ISU Extension Integrated Crop Management Newsletter
June 18, 1993

Postemergence options in soybeans
by M. D. K. Owen, extension weed management specialist

Assure II
can be applied at 5 to 10 ounces of product per acre, depending on the grass species. Apply Assure II when grasses are actively growing and in the suggested stage of development. Include a petroleum oil concentrate or non-ionic surfactant with applications. Do not use a vegetable-based additive. Assure II may demonstrate antagonism attributable to tank mix applications with herbicides used for broadleaf weed control. Assure II can be applied in combination with Basagran, Classic, Concert, Pinnacle, or Pursuit.

Basagran
application should be timed for weed size. Treatment is most effective on smaller, actively growing weeds in the 2- to 4-leaf stage of development. Spray coverage is critical for control; use nozzles that allow uniform distribution of the herbicide on the weeds. Basagran will provide some control of yellow nutsedge and Canada thistle. Additives such as crop oil concentrate, AMS or UAN improve the control of larger weeds. Do not use AMS, or UAN in combination with crop oil concentrate. Basagran can be tank mixed with Blazer, Reflex, 2,4-DB, Scepter, Poast Plus, Pinnacle and Pursuit.

Blazer
should be applied to actively growing weeds in the 2- to 4-leaf stage of development. Apply Blazer in accordance with the weed size. The weed size determines the rate of Blazer. Control is best when weeds are not stressed, either from cool conditions or dry weather. Some grass control may result from Blazer applications. Complete coverage is necessary for optimum control. Crop injury can occur from Blazer, however typically the injury does not reduce yields. Blazer can be applied in combination with Basagran, Poast Plus, 2,4-DB, Classic, Fusilade 2000, Pursuit, Pinnacle, and Scepter.

Classic
can be applied postemergence at 0.5 to 0.75 ounces product per acre. Most broadleaf weeds should be 2 to 4 inches tall for best results. Cocklebur may be up to 12 inches tall, and wild sunflowers can be up to 8 inches tall. Classic can be applied on all soils in Iowa without regard to pH except for Clarion-Nicollet-Webster and Hamburg-Ida-Monona soil associations, and the historic flood plain of the Missouri River. Classic is registered for application on STS soybeans. Classic can be applied in combination with Assure II, Pinnacle, 2,4-DB, and Cobra.

Cobra
should be applied when weeds are actively growing and have no more than four to six leaves, depending on the species. Cobra rate of application should be adjusted with consideration to the relative humidity. Cobra can cause injury to soybeans, however the crop usually recovers without loss of yield. The level of injury depends upon the application rate and environmental conditions. Cobra can be applied in combination with Basagran, Classic, 2,4-DB, Pinnacle, Pursuit, Scepter, Assure II, Fusilade 2000, Select, and Option.

Concert
is a prepackage combination of chlorimuron and thifensulfuron, the active ingredients contained in Classic and Pinnacle, respectively. Concert should be applied to actively growing weeds after the first true leaf has expanded and before they exceed the size limitation on the label, typically 4 to 8 inches, depending on the species. Concert should be applied with either a non-ionic surfactant or crop oil concentrate and an ammonium fertilizer.

Fusilade 2000
should be applied at a rate of 12 to 24 ounces of product per acre to actively growing grasses in the appropriate stage of development. A special rate of 20 ounces per acre is registered for specific grass weeds. Volunteer corn can be controlled from 12 to 24 inches tall. Fusilade 2000 can be applied in combination with Reflex, Basagran, Blazer, Classic, and Pursuit. However, when Fusilade 2000 is applied in combination with herbicides that control broadleaf weeds, some loss of grass control can occur.

Fusion
is a prepackage mixture of fluazifop-p-butyl and fenoxaprop, the active materials in Fusilade 2000 and Option, respectively. Application restrictions are similar to those listed for Fusilade 2000. Apply 6 to 10 ounces of Fusion per acre. The rate may be increased when Fusion is applied in combination with herbicides applied for broadleaf weed control. Fusion may be applied in combination with Reflex, Basagran, Classic, Blazer, and Pursuit. However, when Fusion is applied in combination with herbicides that control broadleaf weeds, some loss of grass control can occur.

Galaxy
is a prepackage combination of acifluorfen and bentazon, the active materials in Blazer and Basagran, respectively. Application should be timed with regard to weed size and growing conditions. The control of pigweeds may not be excellent due to the ratio of acifluorfen to bentazon. Galaxy may be applied in combination with Classic, Pinnacle, 2,4-DB, and Pursuit. See comments for Basagran and Blazer.

Pinnacle
should be applied to actively growing weeds at 0.25 ounces product per acre. Pinnacle does not have a soil pH restriction. The choice of adjuvant should reflect the growing conditions. Refer to the label for specific information. Pinnacle may be applied in combination with herbicides for grass control, however, do not tank mix Pinnacle with Poast Plus. Injury from Pinnacle may result in stunting, malformation of leaves, and purple veination. However, this injury typically does not reduce yields. Pinnacle can be applied in combination with Basagran, Classic, Assure II, Galaxy, and Pursuit.

Poast Plus
should applied to actively growing grass weeds within the recommended stage of growth. Do not apply within 90 days of harvest. Poast Plus may be applied in combination with Basagran. Application of herbicides for broadleaf weed control within 7 days prior to or 1 day following Poast Plus application may reduce annual grass control.

Pursuit
should be applied to actively growing weeds and before weeds exceed the maximum size specified on the label. For most species, the maximum size is 3 inches. Do not apply within 85 days of harvest and prior to soybean bloom. Refer to the label for suggested herbicide additives. Control of some pigweed species may not be good. Pursuit may be applied in combination with Assure II, Basagran, Blazer, Cobra, Fusilade 2000, Galaxy, Option, Poast Plus, Select, Storm, Pinnacle, and Scepter.

Reflex
should be applied at a rate of 1 to 1.5 pints of product per acre to actively growing weeds. Application timing and rate are determined by weed size. Apply before soybeans bloom. Do not apply Reflex to any field more than once every two years. Reflex may be applied in combination with Basagran, 2,4-DB, Classic, Fusilade 2000, Fusion, and Scepter.

Scepter
should be applied at a rate of 0.33 pints of product per acre. This treatment will primarily control cocklebur and pigweeds. Do not apply if the soybeans are under stress.

Select
should be applied to actively growing grass weeds. Apply Select prior to 60 days before soybean harvest. Select may be applied in combination with Basagran, Blazer, Classic, Cobra, Reflex, and Pursuit. However, when Select is applied in combination with herbicides that control broadleaf weeds, some loss of grass control can occur.