CORN Newsletter: 2009-33, September 29, 2009

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C.O.R.N Newsletter 2009-33
September 29, 2009 - October 5, 2009

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Harvest Aids for Corn and Soybeans
by Mark Loux


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Large weeds present at the time of crop harvest can slow the rate of crop maturation, slow the rate of harvest, and increase mechanical stress on equipment. There are essentially two ways to reduce the green weed biomass in the field in order to facilitate harvesting: 1) delay harvest until after a hard freeze (less than 25 degrees F for several hours); or 2) apply herbicides to control and desiccate the weeds. Waiting a week or so after the freeze or herbicide application will allow the weeds to desiccate to a greater extent and become more brittle.

Many glyphosate products can be used in a preharvest treatment in corn or soybeans – check labels for specific uses and rates. In corn, apply glyphosate at least 7 days before harvest when grain moisture is 35% or less. Corn should be physiologically mature (black layer formed) with maximum kernel fill complete. In soybeans, apply glyphosate after the pods have set and lost all green color, and at least 7 or 14 days before harvest, depending upon the glyphosate product. Most glyphosate product labels recommend avoiding preharvest application to corn or soybeans grown for seed, due to the potential for a reduction in seed germination or vigor.

Gramoxone and Parazone can be applied as preharvest treatments in field corn, seed corn, popcorn and soybeans. Apply when corn is mature, or after the black layer has formed at the base of the kernels, and at least 7 days before harvest. In soybeans, apply at least 15 days before harvest when at least 65% of the pods have reached a mature brown color or when seed moisture is 30% or less. Apply with crop oil concentrate (1.0 % v/v) or surfactant (0.25 % v/v). Use a spray volume of at least 20 gpa in ground applications, and 5 gpa for aerial application.

Aim is labeled as a preharvest treatment for corn and soybeans for desiccation of velvetleaf, morningglory, pigweeds, and other annual weeds. Apply at least 3 days before harvest, when the crop is mature and grain has begun to dry down. The rate is 1 to 2 oz/A, and it should be applied with nonionic surfactant (0.25% v/v) or crop oil concentrate (1 to 2% v/v). Rage D-Tech (premix of Aim and 2,4-D) can be used as a preharvest treatment in corn only. The rate is 16 to 32 oz/A, and guidelines for timing and adjuvant use are similar to Aim.

Other Considerations:
1. The greener the weeds, the more effective the treatments (including a freeze) and greater likelihood of reducing weed seed viability. Herbicides will not necessarily reduce the viability of seeds that have formed by the time of application.

2. In general, herbicides will be most effective when applied under warm, sunny conditions.

3. Glyphosate can control perennial weeds that are in the appropriate growth stage at the time of application.

4. Herbicide treatments and freezing weather will not necessarily force loss of fruit on black nightshade plants, or other fruit-bearing weeds.

Readers can subscribe electronically to this newsletter by signing up at http://agcrops.osu.edu/services/email.html. E-mail labarge.1@osu.edu if you have problems subscribing or no longer wish to receive this newsletter.

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868


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