Selecting burndown options for no-till
by Bob Hartzler and Mike Owen, extension weed scientists, Department of Agronomy

Fields that will be planted no-till are starting to green up due to new weed growth. Controlling these weeds at planting is the first step of a successful weed management program. To select the most appropriate burndown herbicide and the proper rate, scout the field a few days before application. Look for weed species present, weed size, and population density. Most annual weeds are still relatively small and should be fairly easy to control. However, the required rate of a specific herbicide depends on what species are present. Winter annuals and perennials are usually more noticeable at this time because of their early spring growth; in most situations, considerably more herbicide is needed to control them than is needed to control summer annual weeds. However, in many fields, winter annual or perennial weeds are present as scattered infestations. Although the presence of these weeds may make a field look bad, their low level of competitiveness may not justify the added expense of a burndown herbicide.

While there are no thresholds available to help you determine when they warrant control, populations of winter annuals of less than one plant per ten square feet probably dont warrant special treatment.

Corn planting after ammonia application
by Regis Voss, extension agronomist, Department of Agronomy

The delay in field work in most parts of Iowa will shorten the time between ammonia (NH3) application and corn planting. So, how soon can you plant corn after applying NH3? The key is having a soil separation between the ammonia zone and the seed.

Depth of injection is extremely important. Ammonia usually diffuses 2 1/2 to 3 inches from the point of injection. But, if wet soil causes the injection knife to seal the sides of the injection slot and limits diffusion of ammonia, ammonia may concentrate below the soil covering or seal. If this happens, and you place seed in the ammonia zone, the longer you wait between applying ammonia and planting corn, the less corn roots will be affected. No magic number of days of waiting will eliminate potential problems if seed is placed in the ammonia zone.

Ammonia injury is detected more frequently in dry weather, because roots are slow to develop and a portion of the root system is injured. You will first notice uneven emergence, slow growth of injured plants, and in dry soil, wilting plants. Browning of roots indicates root injury. In severe cases, dead roots will turn black, even back to the seed.

If you apply ammonia at the proper depth and achieve soil separation between the ammonia zone and seed, you can plant corn immediately after you apply ammonia.

Growing degrees
by Rich Pope, extension program specialist, Department of Entomology

Each crop season, the Integrated Crop Management publishes accumulated growing degree days so you can use them to monitor the development of several major crop pests. This year we changed the format to more clearly communicate information you can use in the field.

Starting with this issue, we will average degree day accumulations across the nine crop reporting districts in Iowa. We begin this week with base-48 accumulations for alfalfa weevil development. Scouting for alfalfa weevil activity should begin around 200 accumulated base-48 degree days in the three southern districts and around 250 degree days in the northern two-thirds of Iowa.

Alfalfa weevil scouting should begin this week in the southern third of Iowa. Use degree days as effective guides in developing pest-specific scouting and treatment plans individual sites may be warmer or colder than the average for a district. For example, the 200 degree threshold has already been reached at the Burlington reporting station, and accumulated degree days are just slightly above the reporting district average (136) at Ottumwa.

Alfalfa weevil eggs have accumulated sufficient degree days (200) to hatch in parts of Des Moines County. Surrounding counties should have weevils hatching by April 21-23. In the next issue of this newsletter, we will publish information on alfalfa weevil scouting and economic thresholds. (Also, see last years newsletter, page 46).

Wireworm fields needed for research

by Marlin E. Rice, extension entomologist, Department of Entomology

Corn fields with wireworms are being sought as locations to conduct research. Wireworm problems are mostly likely to occur in corn planted into pasture or sod ground that had grass for three or more years. If you know of a corn field that has wireworm problems, or one that will need replanting this spring because of this insect, please call me at 515-294-1101. Information gained from this research will be used to make recommendations in future years.

The European corn borer guarantee and Furadan 4F
by Marlin E. Rice, extension entomologist, Department of Entomology

This spring, FMC Corporation is pro-moting the use of Furadan 4F applied post planting to corn as a preventive treatment for first generation European corn borers. Their promotion guarantees rootworm control and first generation European corn borer protection. I have reservations about the benefits of this use from both economic and integrated pest management per-spectives. My concerns are similar to those I expressed about the Pounce 3.2EC cutworm guarantee, discussed in the last issue of the ICM newsletter. The following discussion of my concerns concludes with acceptable alternatives from an integrated pest management perspective.

Concern #1. Preventive insecticide treatments. FMC suggests that Furadan 4F applied post plant for corn rootworms (normally May 15 to June 15) also will provide corn borer protection. Using a broad-spectrum, synthetic insecticide in the absence of an economically damaging corn borer population cannot be justified as a preventive treatment, especially if a rescue treatment provides better control.

Concern #2. Insecticide performance. Entomologists at the University of Nebraska evaluated the Furadan 4F treatment in 1993 and 1994. Each year, plots were sprayed on two dates. The earlier spray was timed to coincide with corn rootworm hatch, and the later spray was timed to match the natural occurrence of first generation corn borers. All plots were artificially infested with corn borer egg masses when wild moths normally lay eggs. Artificial infestation assured that all treatments had an equal number of corn borers. Insecticides were either broadcast or banded, and cultivated or not cultivated.

During 1993, Furadan, Counter, and Lorsban applied early post plant resulted in more corn borers per plant than when the insecticides were applied later, during the normal corn borer egg- laying dates. In 1994, similar results were seen: the early insecticide treatment resulted in more larvae per plant. In several insecticide treatments, there were more corn borers than in the untreated checks.

These data suggest that an early application of Furadan 4F applied post plant for corn rootworms may not reduce the European corn borer population, but might create a problem. The exact reasons that there were more corn borers in the early-sprayed plots are not known. Possibly many beneficial insects were killed, their populations had not yet recovered when the corn borers attacked the plants, and the chemical residue was not persistent enough to kill the corn borers.

Concern #3. Insecticide guarantee. FMC promotional material states that the guarantee reduces your risk in using a new application method to control two of the most important pests. The Nebraska data suggest that your risk from corn borer injury actually may increase. It is very important not to be lulled into a false sense of security by this guarantee. The guarantee is subject to the condition that the field must be scouted for insect injury. Spraying the field early in the season doesnt preclude the possibility of crop injury by insects.

The guarantee provides Pounce 1.5G to retreat the field if the corn borers exceed the economic threshold. But that means you apply insecticide twice, while if you had applied a corn rootworm insecticide at planting, the rescue Pounce treatment may not have been needed.

Concern #4. Field scouting. For the guarantee to be valid, you must check the field and determine if corn borer injury exceeds economic thresholds. Remember, the Furadan guarantee allows for the failure of the insecticide; you must scout the field, and monitor product performance.

The alternative. There is a better way to manage European corn borers than by applying an insecticide that may aggravate an insect infestationscout the fields for corn borers. This newsletter will issue reports when corn borers are found and provide information on how to scout and determine the economic threshold. Then you can scout the field, look for early signs of injury, and determine if the economic threshold has been reached. This allows you to apply insecticide when it is really needed and economically justified.

Using Furadan, or any other insecticide, as a preventive treatment in the absence of economically damaging (or potentially damaging) insect populations is irresponsible stewardship of the insecticide and goes against the principles of integrated pest management. Remember: use your insecticides wisely.

Pesticide recordkeeping law amended
by Joyce Hornstein, extension program specialist, Department of Entomology

Are you ready to record your restricted use pesticide applications? If you are a private pesticide applicator, you must do so if you apply restricted use pesticides this crop season.

The original recordkeeping regulation (see sidebar) has been revised to include the following, effective May 11, 1995:

1. Certified private applicators now must record each restricted use pesticide application within 14 days. Previously, the time period was 30 days. The certified applicator also must provide information for medical treatment or first aid, whether or not the written record has been completed.

2. The location description on the spot application record must now include a concise description of location and treatment. A spot application is any application made on the same day in a total area of less than one-tenth of an acre. For example, a certified applicator who applied pesticides for noxious weeds could record the location and treatment as a spot application, with an explanation such as treated thistle throughout field number 6.

3. Information provided to the attending licensed health care professional also must be made available to individuals acting under the direction of that professional so they can treat those who have been exposed to a restricted use pesticide.

When must I record the information? The required information must be recorded within 14 days following the pesticide application, so dont put off completing your application records!

How long must records be saved? Applicators must retain restricted use pesticide records for two years from the date of application. The records must be made available to authorized individuals.

If a private applicator buys a restricted use pesticide so that a commercial applicator can apply it, who creates and maintains the record? The commercial applicator must generate the record if he or she makes the application. The commercial applicator is required both to maintain the record and to provide a copy of the record to the private applicator within 30 days. Note that this time period did not change from earlier requirements.

Is a special form needed? No, the regulation does not require you to use a standardized form. This allows applicators to fit the requirements into their current recordkeeping system.

What are the penalties for violation of the Federal pesticide recordkeeping requirements? Any certified applicator who violates the requirements is subject to a civil penalty of not more than $500 in the case of the first offense. Each subsequent violation is subject to a civil penalty of not less than $1,000, unless the Administrator determines the applicator made a good faith effort to comply.

Recordkeeping publications

Two ISU Extension publications, available at your county extension office, can help you with the restricted use pesticide recordkeeping requirements.

The Field Records for Integrated Crop Management and Restricted Use Pesticide Applications pocket guide includes space for information on ten fields. It also contains a directory of EPA registration numbers for commonly used restricted use pesticides. Ask for ICM-1 at your county extension office. The cost is $1.

A free publication, PAT-11, is being revised and will be available about May 20.

Recordkeeping requirements of the 1990 Farm Bill

The recordkeeping requirements for private pesticide applicators originally went into effect in May 1993, as a provision of the 1990 Farm Bill. The law required private pesticide applicators to keep records of all restricted use pesticide applications. This is very similar to the recordkeeping requirements for commercial applicators.

The Bill states that a certified private pesticide applicator must record:

1. The brand or product name, and the EPA registration number of the restricted use pesticide that was applied.

2. The total amount of the restricted use pesticide applied.

3. The location of the application, the size of area treated, and the crop, commodity, stored product, or site to which a restricted use pesticide was applied. The location of the application may be recorded using any of the following:
   1. county, range, township, and section;
      
   2. an identification system using maps and/or written descriptions that accurately identify location;
      
   3. an identification system established by a USDA agency that uses maps and a numbering system to identify field locations; or
      
   4. legal property description.

4. The month, day, and year when the restricted use pesticide application occurred.

5. The name and certification number of the certified applicator who applied or who supervised the application of the restricted use pesticide.

Reduced rates of corn rootworm insecticides
by Marlin E. Rice, extension entomologist, Department of Entomology

Farmers throughout the Midwest are using soil insecticides for corn rootworm control at a lower rate than the amount stated on the insecticide label. This is called a reduced rate. Their primary motivations for using a reduced rate are to save money by lowering the cost of growing corn and to reduce the amount of insecticide entering the environment.

Farmers need to know if a reduced rate will provide the same amount of protection as the labeled rate. Answers to reduced rate insecticide performance questions, based on the latest available research, follow.

Has Iowa State University tested the performance of reduced rates? Yes, from 1988 through 1992, five insecticides were evaluated under a variety of environmental conditions, ranging from dry in 1988 and 1992 to very wet in 1991. Insecticides were t-banded at the full-label rate (8 oz./1,000 row feet for 15G and 1.5G material; 6 oz./1,000 row feet for 20G material) and at 34 and 12 these rates. Counter and Force also were tested in furrow. Roots were examined in July for root injury. Each insecticide was given a consistency rating based on the percentage of tests in which adequate root protection was achieved.

How did the reduced rates perform? All five insecticides were just as consistent in providing root protection at the 34-label rate as at the full rate, except Force in furrow (see table). Consistency at the 12-label rate, compared to the full rate, was also good for Counter and Lorsban, but not for Dyfonate and Thimet. The 12-label rate was not tested for Force. Similar results have been found by entomologists at other midwestern universities.

Two other items are worth noting. First, no insecticide applied at the full rate gave complete protection all the time; if it had, a 100% would appear in that column. When an insecticide failed at the full rate, the 34 rate failed an equal number of times. Second, you will notice that Lorsban at the 34-rate had a consistency percentage that was numerically larger than Lorsban at the full-label rate. This is a result of experimental variation over the years and test sites, but statistically there was no difference in root protection between the two rates.

An asterisk (*) occurring beside a number in the table indicates that the rate was statistically different from the full rate and did not provide the same level of root protection.

What is the position of the insecticide manufacturers? No manufacturer has reduced the rate normally stated on their insecticide labels during recent years. Therefore, no chemical manufacturer is promoting reduced rates. If you decide to use a reduced rate, the manufacturer would not be legally obliged to warranty the performance of their product.

What should I consider if I use a reduced rate? First, you must calibrate all insecticide boxes on the planter before planting so the exact rate can be applied. When you cut the rate, there is less room for error. Second, select an insecticide and application method that performs well at the 34 rate (see table). Third, start out on a few acres to determine if this fits into your farming operation. Plant strips at both the full rate and a reduced rate. Then dig roots in July and make comparisons in performance. Fourth, remember that it is not illegal to use a reduced rate of an insecticide.