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Todd Vagts
Iowa State University Extension
Field Crops Specialist
1240 D. Heires Avenue Office: 712-792-2364
Carroll, IA 51401 Cell: 712-249-6025
Email: vagts@iastate.edu Fax: 712-792-2366

When will the wind stop blowing? Along with the wind have been many successive warm and dry days that have allowed a tremendous amount of corn to be put in the ground in a short period of time. My concern now is to keep the seedbed moist and prevent the soil moisture line from dropping below the newly planted seed. As I mentioned in last week’s newsletter, monitor your fields to make sure that the germinating seed remains in good soil moisture. If the seedbed dries out after the seed has germinated, in most cases replanting is necessary. This situation rarely occurs across an entire field, but often is in scattered areas where the soil may have been cloddy, manured areas of the field, or may be isolated to certain planter rows due to slight differences in planting depths. With windy conditions also come increased problems and risks when applying herbicides. Be overly cautious and use equipment now available that help reduce drift during application.

Growing degree days are calculated by the following equation:

(Daily high temp + Daily low temp)/2 – base temperature. The base temperature for corn is 50 degrees F and is 55 degrees F for soybean. A maximum temperature of 86 degrees F is also used. Corn typically requires 110 GDD50’s for emergence. This number will vary depending on soil temperature, soil type, planting depth, and soil moisture. According to the cumulative GDD50’s that I have calculated, corn planted in Monona, Crawford, Carroll, Ida, Sac, and Calhoun counties from April 20th – 23rd should be emerging now. (Table 1) Corn planted in Pocahontas and Buena Vista counties on April 20 should be emerging today or within the next couple of days (Table 1).

With the quick turnaround that we have seen between anhydrous ammonia application and corn planting the question often arises as to how long to wait to plant corn after ammonia application. If there is a soil separation between the ammonia zone and the seed, planting can be done the same day the ammonia is applied. If the seed is to be placed in the ammonia zone, the longer the waiting period the less potential for root injury. There is no magic number of days to wait.

The depth of ammonia application is extremely important. The depth should be checked in the field. Use a spade to dig down through the injection zone to check depth. Ammonia should be injected 7 to 8 inches deep to minimize potential injury. Where possible, ammonia application at a slight angle to row direction will reduce the number of plants affected.

Ammonia injury causes desiccation of roots and die-back from the root tips. Injury is first noted in the field by uneven emergence, slow growth of some plants, and wilting of plants in dry weather. Root injury is noted by browning of the roots and in severe cases roots will be completely killed and turned black back to the seed. Ammonia injury is detected more frequently in dry weather because roots are slow to develop and destruction of a portion of the root systems limits water uptake.

(Information from Integrated crop mngt 4-16-93 Regis Voss, extension agronomist)

Use nozzles that produce large spray droplets. Droplet size is the major factor influencing herbicide drift. Small droplets take more time to fall to the ground and can thus drift farther. It is desirable to use a nozzle that produces large, uniform droplets. Switching from standard flat-fan nozzles (such as an XR11003) to turbulence-chamber or venturi nozzles increases droplet size and can greatly reduce the amount of drift. Examples of such nozzles are Turbo TeeJet and AI TeeJet nozzles (Spraying Systems Co.), Raindrop Ultra (Delavan), and the TurboDrop (Greenleaf Technologies).

Droplet size can have a negative effect on herbicide performance when coverage is reduced. The droplet size produced by these nozzles should have no effect on performance for systemic herbicides, including burndown applications involving growth regulators or glyphosate. Contact herbicides, such as Buctril, Cobra, and Reflex, require adequate target coverage for maximum effectiveness and may have required nozzle and pressure combinations that produce smaller droplets. Always consult the herbicide label for specific recommendations or restrictions on equipment selection

(An applicator's drift reduction checklist, by Brent Pringnitz)